Sets the application name for a client session. For example, if connecting via psql, this will be set to psql. Setting an application name allows it to be reported in log messages and statistics views.

This controls whether the array input parser recognizes unquoted NULL as specifying a null array element. By default, this is on, allowing array values containing null values to be entered. Greenplum Database versions before 3.0 did not support null values in arrays, and therefore would treat NULL as specifying a normal array element with the string value 'NULL'.

Maximum time to complete client authentication. This prevents hung clients from occupying a connection indefinitely.

This controls whether a quote mark can be represented by \' in a string literal. The preferred, SQL-standard way to represent a quote mark is by doubling it ('') but PostgreSQL has historically also accepted \'. However, use of \' creates security risks because in some client character set encodings, there are multibyte characters in which the last byte is numerically equivalent to ASCII \.

Reports the size of a disk block.

Specifies the Bonjour broadcast name. By default, the computer name is used, specified as an empty string. This option is ignored if the server was not compiled with Bonjour support.

When set to off, disables validation of the function body string during CREATE FUNCTION. Disabling validation is occasionally useful to avoid problems such as forward references when restoring function definitions from a dump.

Sets the client-side encoding (character set). The default is to use the same as the database encoding. See Supported Character Sets in the PostgreSQL documentation.

Controls which message levels are sent to the client. Each level includes all the levels that follow it. The later the level, the fewer messages are sent.

INFO level messages are always sent to the client.

For the Postgres Planner, sets the estimate of the cost of processing each index row during an index scan. This is measured as a fraction of the cost of a sequential page fetch.

For the Postgres Planner, sets the estimate of the cost of processing each operator in a WHERE clause. This is measured as a fraction of the cost of a sequential page fetch.

For the Postgres Planner, Sets the estimate of the cost of processing each row during a query. This is measured as a fraction of the cost of a sequential page fetch.

Tells the Postgres Planner how many rows are expected to be fetched in a cursor query, thereby allowing the Postgres Planner to use this information to optimize the query plan. The default of 1 means all rows will be fetched.

Reports whether checksums are enabled for heap data storage in the database system. Checksums for heap data are enabled or disabled when the database system is initialized and cannot be changed.

Heap data pages store heap tables, catalog tables, indexes, and database metadata. Append-optimized storage has built-in checksum support that is unrelated to this parameter.

Greenplum Database uses checksums to prevent loading data corrupted in the file system into memory managed by database processes. When heap data checksums are enabled, Greenplum Database computes and stores checksums on heap data pages when they are written to disk. When a page is retrieved from disk, the checksum is verified. If the verification fails, an error is generated and the page is not permitted to load into managed memory.

If the ignore_checksum_failure configuration parameter has been set to on, a failed checksum verification generates a warning, but the page is allowed to be loaded into managed memory. If the page is then updated, it is flushed to disk and replicated to the mirror. This can cause data corruption to propagate to the mirror and prevent a complete recovery. Because of the potential for data loss, the ignore_checksum_failure parameter should only be enabled when needed to recover data. See ignore_checksum_failure for more information.

Sets the display format for date and time values, as well as the rules for interpreting ambiguous date input values. This variable contains two independent components: the output format specification and the input/output specification for year/month/day ordering.

This enables per-database user names. If on, you should create users as username@dbname. To create ordinary global users, simply append @ when specifying the user name in the client.

The time to wait on a lock before checking to see if there is a deadlock condition. On a heavily loaded server you might want to raise this value. Ideally the setting should exceed your typical transaction time, so as to improve the odds that a lock will be released before the waiter decides to check for deadlock.

Turns on various assertion checks.

Indents debug output to produce a more readable but much longer output format. client_min_messages or log_min_messages must be DEBUG1 or lower.

For each executed query, prints the resulting parse tree. client_min_messages or log_min_messages must be DEBUG1 or lower.

For each executed query, prints the Greenplum parallel query execution plan. client_min_messages or log_min_messages must be DEBUG1 or lower.

For each executed query, prints the preliminary query plan. client_min_messages or log_min_messages must be DEBUG1 or lower.

For each executed query, prints the query rewriter output. client_min_messages or log_min_messages must be DEBUG1 or lower.

For each executed query, prints the Greenplum query slice plan. client_min_messages or log_min_messages must be DEBUG1 or lower.

Sets the default statistics sampling target (the number of values that are stored in the list of common values) for table columns that have not had a column-specific target set via ALTER TABLE SET STATISTICS. Larger values may improve the quality of the Postgres Planner estimates.

The default tablespace in which to create objects (tables and indexes) when a CREATE command does not explicitly specify a tablespace.

Selects the text search configuration that is used by those variants of the text search functions that do not have an explicit argument specifying the configuration. See Using Full Text Search for further information. The built-in default is pg_catalog.simple, but initdb will initialize the configuration file with a setting that corresponds to the chosen lc_ctype locale, if a configuration matching that locale can be identified.

When running at the SERIALIZABLE isolation level, a deferrable read-only SQL transaction may be delayed before it is allowed to proceed. However, once it begins executing it does not incur any of the overhead required to ensure serializability; so serialization code will have no reason to force it to abort because of concurrent updates, making this option suitable for long-running read-only transactions.

Controls the default isolation level of each new transaction. Greenplum Database treats read uncommitted the same as read committed, and treats serializable the same as repeatable read.

Controls the default read-only status of each new transaction. A read-only SQL transaction cannot alter non-temporary tables.

If a dynamically loadable module needs to be opened and the file name specified in the CREATE FUNCTION or LOAD command does not have a directory component (i.e. the name does not contain a slash), the system will search this path for the required file. The compiled-in PostgreSQL package library directory is substituted for $libdir. This is where the modules provided by the standard PostgreSQL distribution are installed.

Sets the assumption about the effective size of the disk cache that is available to a single query for the Postgres Planner. This is factored into estimates of the cost of using an index; a higher value makes it more likely index scans will be used, a lower value makes it more likely sequential scans will be used. This parameter has no effect on the size of shared memory allocated by a Greenplum server instance, nor does it reserve kernel disk cache; it is used only for estimation purposes.

Set this parameter to a number of 32K blocks (for example, 512 for 16MB), or specify the size of the effective cache (for example, '32MB' for 1024 blocks). The gpconfig utility and SHOW command display the effective cache size value in units such as 'MB' or 'kB'.

Enables or disables the use of bitmap-scan plan types by the Postgres Planner. Note that this is different than a Bitmap Index Scan. A Bitmap Scan means that indexes will be dynamically converted to bitmaps in memory when appropriate, giving faster index performance on complex queries against very large tables. It is used when there are multiple predicates on different indexed columns. Each bitmap per column can be compared to create a final list of selected tuples.

Enables or disables the use of group aggregation plan types by the Postgres Planner.

Enables or disables the use of hash aggregation plan types by the Postgres Planner.

Enables or disables the use of hash-join plan types by the Postgres Planner.

Enables or disables the use of index-scan plan types by the Postgres Planner.

Enables or disables the use of merge-join plan types by the Postgres Planner. Merge join is based on the idea of sorting the left- and right-hand tables into order and then scanning them in parallel. So, both data types must be capable of being fully ordered, and the join operator must be one that can only succeed for pairs of values that fall at the 'same place' in the sort order. In practice this means that the join operator must behave like equality.

Enables or disables the use of nested-loop join plans by the Postgres Planner. It's not possible to suppress nested-loop joins entirely, but turning this variable off discourages the Postgres Planner from using one if there are other methods available.

Enables or disables the use of sequential scan plan types by the Postgres Planner. It's not possible to suppress sequential scans entirely, but turning this variable off discourages the Postgres Planner from using one if there are other methods available.

Enables or disables the use of explicit sort steps by the Postgres Planner. It's not possible to suppress explicit sorts entirely, but turning this variable off discourages the Postgres Planner from using one if there are other methods available.

Enables or disables the use of tuple identifier (TID) scan plan types by the Postgres Planner.

When on, a warning is issued if a backslash (\) appears in an ordinary string literal ('...' syntax). Escape string syntax (E'...') should be used for escapes, because in future versions, ordinary strings will have the SQL standard-conforming behavior of treating backslashes literally.

Determines whether EXPLAIN VERBOSE uses the indented or non-indented format for displaying detailed query-tree dumps.

Adjusts the number of digits displayed for floating-point values, including float4, float8, and geometric data types. The parameter value is added to the standard number of digits. The value can be set as high as 3, to include partially-significant digits; this is especially useful for dumping float data that needs to be restored exactly. Or it can be set negative to suppress unwanted digits.

The Postgres Planner will merge sub-queries into upper queries if the resulting FROM list would have no more than this many items. Smaller values reduce planning time but may yield inferior query plans.

Enables the selectivity of NULL tests over outer joins.

Enables compacting segment files during VACUUM commands. When disabled, VACUUM only truncates the segment files to the EOF value, as is the current behavior. The administrator may want to disable compaction in high I/O load situations or low space situations.

Specifies the threshold ratio (as a percentage) of hidden rows to total rows that triggers compaction of the segment file when VACUUM is run without the FULL option (a lazy vacuum). If the ratio of hidden rows in a segment file on a segment is less than this threshold, the segment file is not compacted, and a log message is issued.

Specifies the mode for triggering automatic statistics collection with ANALYZE. The on_no_stats option triggers statistics collection for CREATE TABLE AS SELECT, INSERT, or COPY operations on any table that has no existing statistics.

The on_change option triggers statistics collection only when the number of rows affected exceeds the threshold defined by gp_autostats_on_change_threshold. Operations that can trigger automatic statistics collection with on_change are:

CREATE TABLE AS SELECT

UPDATE

DELETE

INSERT

COPY

Default is on_no_stats.

Specifies the mode for triggering automatic statistics collection with ANALYZE for statements in procedural language functions. The none option disables statistics collection. The on_no_stats option triggers statistics collection for CREATE TABLE AS SELECT, INSERT, or COPY operations that are executed in functions on any table that has no existing statistics.

The on_change option triggers statistics collection only when the number of rows affected exceeds the threshold defined by gp_autostats_on_change_threshold. Operations in functions that can trigger automatic statistics collection with on_change are:

CREATE TABLE AS SELECT

UPDATE

DELETE

INSERT

COPY

Specifies the threshold for automatic statistics collection when gp_autostats_mode is set to on_change. When a triggering table operation affects a number of rows exceeding this threshold, ANALYZE is added and statistics are collected for the table.

When a user starts a session with Greenplum Database and issues a query, the system creates groups or 'gangs' of worker processes on each segment to do the work. After the work is done, the segment worker processes are destroyed except for a cached number which is set by this parameter. A lower setting conserves system resources on the segment hosts, but a higher setting may improve performance for power-users that want to issue many complex queries in a row.

Shows how many commands the master has received from the client. Note that a single SQLcommand might actually involve more than one command internally, so the counter may increment by more than one for a single query. This counter also is shared by all of the segment processes working on the command.

The local content id if a segment.

Controls table creation when a Greenplum Database table is created with a CREATE TABLE or CREATE TABLE AS command that does not contain a DISTRIBUTED BY clause.

For information about the Postgres Planner and GPORCA, see "Querying Data" in the Greenplum Database Administrator Guide.

The local content dbid if a segment.

Number of seconds for a Greenplum process to linger after a fatal internal error.

Specify multiple storage option values as a comma separated list.

You can set the storage options with this parameter instead of specifying the table storage options in the WITH of the CREATE TABLE command. The table storage options that are specified with the CREATE TABLE command override the values specified by this parameter.

Not all combinations of storage option values are valid. If the specified storage options are not valid, an error is returned. See the CREATE TABLE command for information about table storage options.

The defaults can be set for a database and user. If the server configuration parameter is set at different levels, this the order of precedence, from highest to lowest, of the table storage values when a user logs into a database and creates a table:

1. The values specified in a CREATE TABLE command with the WITH clause or ENCODING clause
2. The value of gp_default_storage_options that set for the user with the ALTER ROLE...SET command
3. The value of gp_default_storage_options that is set for the database with the ALTER DATABASE...SET command
4. The value of gp_default_storage_options that is set for the Greenplum Database system with the gpconfig utility

The parameter value is not cumulative. For example, if the parameter specifies the appendoptimized and compresstype options for a database and a user logs in and sets the parameter to specify the value for the orientation option, the appendoptimized, and compresstype values set at the database level are ignored.

ALTER DATABASE mytest SET gp_default_storage_options = 'orientation=column, compresstype=rle_type'

To create an append-optimized table in the mytest database with column-oriented table and RLE compression. The user needs to specify only appendoptimized=TRUE in the WITH clause.

gpconfig -c 'gp_default_storage_options' -v 'appendoptimized=true, orientation=column'

gpconfig -s 'gp_default_storage_options'

Enables plans that can dynamically eliminate the scanning of partitions.

Enables or disables two-phase aggregation to compute a single distinct-qualified aggregate. This applies only to subqueries that include a single distinct-qualified aggregate function.

Enables or disables three-phase aggregation and join to compute distinct-qualified aggregates. This applies only to subqueries that include one or more distinct-qualified aggregate functions.

Enables or disables the dispatching of targeted query plans for queries that access data on a single segment. When on, queries that target rows on a single segment will only have their query plan dispatched to that segment (rather than to all segments). This significantly reduces the response time of qualifying queries as there is no interconnect setup involved. Direct dispatch does require more CPU utilization on the master.

Controls availability of the EXCHANGE DEFAULT PARTITION clause for ALTER TABLE. The default value for the parameter is off. The clause is not available and Greenplum Database returns an error if the clause is specified in an ALTER TABLE command.

If the value is on, Greenplum Database returns a warning stating that exchanging the default partition might result in incorrect results due to invalid data in the default partition.

When set to on, the Postgres Planner plans single row inserts so that they are sent directly to the correct segment instance (no motion operation required). This significantly improves performance of single-row-insert statements.

Controls whether the Greenplum Database Global Deadlock Detector is enabled to manage concurrent UPDATE and DELETE operations on heap tables to improve performance. See Global Deadlock Detector. The default is off, the Global Deadlock Detector is disabled.

If the Global Deadlock Detector is disabled (the default), Greenplum Database executes concurrent update and delete operations on a heap table serially.

If the Global Deadlock Detector is enabled, concurrent updates are permitted and the Global Deadlock Detector determines when a deadlock exists, and breaks the deadlock by cancelling one or more backend processes associated with the youngest transaction(s) involved.

Enables or disables the data collection agents that populate the gpperfmon database.

Enables or disables gathering data to a single node to compute distinct-qualified aggregates on grouping extension queries. When this parameter and gp_enable_groupext_distinct_pruning are both enabled, the Postgres Planner uses the cheaper plan.

Enables or disables three-phase aggregation and join to compute distinct-qualified aggregates on grouping extension queries. Usually, enabling this parameter generates a cheaper query plan that the Postgres Planner will use in preference to existing plan.

Enables or disables the use of two or three-stage parallel aggregation plans Postgres Planner. This approach applies to any subquery with aggregation. If gp_enable_multiphase_agg is off, then gp_enable_agg_distinct and gp_enable_agg_distinct_pruning are disabled.

When enabled, the Postgres Planner applies query predicates to both table expressions in cases where the tables are joined on their distribution key column(s). Filtering both tables prior to doing the join (when possible) is more efficient.

Enables two-phase duplicate removal for SELECT DISTINCT queries (not SELECT COUNT(DISTINCT)). When enabled, it adds an extra SORT DISTINCT set of plan nodes before motioning. In cases where the distinct operation greatly reduces the number of rows, this extra SORT DISTINCT is much cheaper than the cost of sending the rows across the Interconnect.

Enables collection of query metrics. When query metrics collection is enabled, Greenplum Database collects metrics during query execution. The default is off.

After changing this configuration parameter, Greenplum Database must be restarted for the change to take effect.

The Greenplum Database metrics collection extension, when enabled, sends the collected metrics over UDP to a Pivotal Greenplum Command Center agent¹.

Enables GPORCA and the Postgres Planner to use the estimated size of a table (pg_relation_size function) if there are no statistics for the table. By default, GPORCA and the planner use a default value to estimate the number of rows if statistics are not available. The default behavior improves query optimization time and reduces resource queue usage in heavy workloads, but can lead to suboptimal plans.

This parameter is ignored for a root partition of a partitioned table. When GPORCA is enabled and the root partition does not have statistics, GPORCA always uses the default value. You can use ANALZYE ROOTPARTITION to collect statistics on the root partition. See ANALYZE.

Controls whether the distribution policy for a table (from the table DISTRIBUTED clause) is checked when data is copied into the table with the COPY FROM...ON SEGMENT command. If true, an error is returned if a row of data violates the distribution policy for a segment instance. The default is true.

If the value is false, the distribution policy is not checked. The data added to the table might violate the table distribution policy for the segment instance. Manual redistribution of table data might be required. See the ALTER TABLE clause WITH REORGANIZE.

The parameter can be set for a database system or a session. The parameter cannot be set for a specific database.

Enable duplicates to be removed while sorting.

Enable LIMIT operation to be performed while sorting. Sorts more efficiently when the plan requires the first limit_number of rows at most.

Enables or disables the use of external tables that execute OS commands or scripts on the segment hosts (CREATE EXTERNAL TABLE EXECUTE syntax). Must be enabled if using the Command Center or MapReduce features.

Sets the number of segments that will scan external table data during an external table operation, the purpose being not to overload the system with scanning data and take away resources from other concurrent operations. This only applies to external tables that use the gpfdist:// protocol to access external table data.

Enable filter pushdown when reading data from external tables. If pushdown fails, a query is executed without pushing filters to the external data source (instead, Greenplum Database applies the same constraints to the result). See Defining External Tables for more information.

Specifies the polling interval for the fault detection process (ftsprobe). The ftsprobe process will take approximately this amount of time to detect a segment failure.

Specifies the number of times the fault detection process (ftsprobe) attempts to connect to a segment before reporting segment failure.

Specifies the number of ftsprobe threads to create. This parameter should be set to a value equal to or greater than the number of segments per host.

Specifies the allowed timeout for the fault detection process (ftsprobe) to establish a connection to a segment before declaring it down.

Specifies the executing interval (in seconds) of the global deadlock detector background worker process.

Controls the amount of detail the fault detection process (ftsprobe) writes to the log file.

Controls the amount of information that is written to the log file about communication between Greenplum Database segment instance worker processes. The default value is terse. The log information is written to both the master and segment instance logs.

Increasing the amount of logging could affect performance and increase disk space usage.

Controls the amount of information that is written to the log file about query worker process creation and query management. The default value is OFF, do not log information.

Sets the frequency that the Greenplum Database server processes send query execution updates to the data collection agent processes used to populate the gpperfmon database. Query operations executed during this interval are sent through UDP to the segment monitor agents. If you find that an excessive number of UDP packets are dropped during long-running, complex queries, you may consider increasing this value.

Controls which message levels are written to the gpperfmon log. Each level includes all the levels that follow it. The later the level, the fewer messages are sent to the log.

Sets the target density of the hash table used by HashJoin operations. A smaller value will tend to produce larger hash tables, which can increase join performance.

Controls Greenplum Database behavior when the deprecated INTO ERROR TABLE clause is specified in a CREATE EXTERNAL TABLE or COPY command.

The default value is false, Greenplum Database returns an error if the INTO ERROR TABLE clause is specified in a command.

If the value is true, Greenplum Database ignores the clause, issues a warning, and executes the command without the INTO ERROR TABLE clause. In Greenplum Database 5.x and later, you access the error log information with built-in SQL functions. See the CREATE EXTERNAL TABLE or COPY command.

You can set this value to true to avoid the Greenplum Database error when you run applications that execute CREATE EXTERNAL TABLE or COPY commands that include the Greenplum Database 4.3.x INTO ERROR TABLE clause.

For the parameter value n, Greenplum Database stops processing input rows when you import data with the COPY command or from an external table if the first n rows processed contain formatting errors. If a valid row is processed within the first n rows, Greenplum Database continues processing input rows.

Setting the value to 0 disables this limit.

The SEGMENT REJECT LIMIT clause can also be specified for the COPY command or the external table definition to limit the number of rejected rows.

INT_MAX is the largest value that can be stored as an integer on your system.

The amount of shared memory, in kilobytes, allocated for query metrics. The default is 5120 and the maximum is 131072. At startup, if gp_enable_query_metrics is set to on, Greenplum Database allocates space in shared memory to save query metrics. This memory is organized as a header and a list of slots. The number of slots needed depends on the number of concurrent queries and the number of execution plan nodes per query. The default value, 5120, is based on a Greenplum Database system that executes a maximum of about 250 concurrent queries with 120 nodes per query. If the gp_enable_query_metrics configuration parameter is off, or if the slots are exhausted, the metrics are maintained in local memory instead of in shared memory.

Specifies the interval, in seconds, to log Greenplum Database interconnect debugging messages when the server configuration parameter gp_log_interconnect is set to DEBUG. The default is 10 seconds.

The log messages contain information about the interconnect communication between Greenplum Database segment instance worker processes. The information can be helpful when debugging network issues between segment instances.

Specifies the flow control method used for the default Greenplum Database UDPIFC interconnect.

For capacity based flow control, senders do not send packets when receivers do not have the capacity.

Loss based flow control is based on capacity based flow control, and also tunes the sending speed according to packet losses.

Sets the amount of data per-peer to be queued by the Greenplum Database interconnect on receivers (when data is received but no space is available to receive it the data will be dropped, and the transmitter will need to resend it) for the default UDPIFC interconnect. Increasing the depth from its default value will cause the system to use more memory, but may increase performance. It is reasonable to set this value between 1 and 10. Queries with data skew potentially perform better with an increased queue depth. Increasing this may radically increase the amount of memory used by the system.

Specifies the amount of time to wait for the Greenplum Database interconnect to complete setup before it times out.

Sets the amount of data per-peer to be queued by the default UDPIFC interconnect on senders. Increasing the depth from its default value will cause the system to use more memory, but may increase performance. Reasonable values for this parameter are between 1 and 4. Increasing the value might radically increase the amount of memory used by the system.

Sets the networking protocol used for Greenplum Database interconnect traffic. UDPIFC specifies using UDP with flow control for interconnect traffic, and is the only value supported.

UDPIFC (the default) specifies using UDP with flow control for interconnect traffic. Specify the interconnect flow control method with gp_interconnect_fc_method.

With TCP as the interconnect protocol, Greenplum Database has an upper limit of 1000 segment instances - less than that if the query workload involves complex, multi-slice queries.

Specifies the format of the server log files. If using gp_toolkit administrative schema, the log files must be in CSV format.

Sets the maximum number of distributed transaction log entries to cache in the backend process memory of a segment instance.

The log entries contain information about the state of rows that are being accessed by an SQL statement. The information is used to determine which rows are visible to an SQL transaction when executing multiple simultaneous SQL statements in an MVCC environment. Caching distributed transaction log entries locally improves transaction processing speed by improving performance of the row visibility determination process.

The default value is optimal for a wide variety of SQL processing environments.

Sets the tuple-serialization chunk size for the Greenplum Database interconnect.

Specifies the total maximum uncompressed size of a query execution plan multiplied by the number of Motion operators (slices) in the plan. If the size of the query plan exceeds the value, the query is cancelled and an error is returned. A value of 0 means that the size of the plan is not monitored.

You can specify a value in kB, MB, or GB. The default unit is kB. For example, a value of 200 is 200kB. A value of 1GB is the same as 1024MB or 1048576kB.

Specifies the maximum number of slices (portions of a query plan that are executed on segment instances) that can be generated by a query. If the query generates more than the specified number of slices, Greenplum Database returns an error and does not execute the query. The default value is 0, no maximum value.

Executing a query that generates a large number of slices might affect Greenplum Database performance. For example, a query that contains UNION or UNION ALL operators over several complex views can generate a large number of slices. You can run EXPLAIN ANALYZE on the query to view slice statistics for the query.

Sets the Postgres Planner cost estimate for a Motion operator to transfer a row from one segment to another, measured as a fraction of the cost of a sequential page fetch. If 0, then the value used is two times the value of cpu_tuple_cost.

Controls the availability of the RECURSIVE keyword in the WITH clause of a SELECT [INTO] command, or a DELETE, INSERT or UPDATE command. The keyword allows a subquery in the WITH clause of a command to reference itself. The default value is false, the RECURSIVE keyword is not allowed in the WITH clause of a command.

For information about the RECURSIVE keyword (Beta), see the SELECT command and WITH Queries (Common Table Expressions).

The parameter can be set for a database system, an individual database, or a session or query.

For single row error handling on COPY and external table SELECTs, sets the number of rows processed before SEGMENT REJECT LIMIT n PERCENT starts calculating.

If enabled, will attempt to dump core if a fatal server error occurs.

Used by a resource group to manage memory allocation to query operators.

When set to auto, Greenplum Database uses resource group memory limits to distribute memory across query operators, allocating a fixed size of memory to non-memory-intensive operators and the rest to memory-intensive operators.

When you specify eager_free, Greenplum Database distributes memory among operators more optimally by re-allocating memory released by operators that have completed their processing to operators in a later query stage.

Enables or disables the enforcement of resource group concurrent transaction limits on Greenplum Database resources. The default value is false, which enforces resource group transaction limits. Resource groups manage resources such as CPU, memory, and the number of concurrent transactions that are used by queries and external components such as PL/Container.

You can set this parameter to true to bypass resource group concurrent transaction limitations so that a query can run immediately. For example, you can set the parameter to true for a session to run a system catalog query or a similar query that requires a minimal amount of resources.

This parameter can be set for a session. The parameter cannot be set within a transaction or a function.

Identifies the maximum percentage of system CPU resources to allocate to resource groups on each Greenplum Database segment node.

Identifies the maximum percentage of system memory resources to allocate to resource groups on each Greenplum Database segment node.

0.7 + (0.116 * 2) = 0.932%

Identifies the resource management scheme currently enabled in the Greenplum Database cluster. The default scheme is to use resource queues.

Enables Greenplum memory management features. The distribution algorithm eager_free takes advantage of the fact that not all operators execute at the same time (in Greenplum Database 4.2 and later). The query plan is divided into stages and Greenplum Database eagerly frees memory allocated to a previous stage at the end of that stage's execution, then allocates the eagerly freed memory to the new stage.

When set to none, memory management is the same as in Greenplum Database releases prior to 4.1.

When set to auto, query memory usage is controlled by statement_mem and resource queue memory limits.

Enables or disables query prioritization. When this parameter is disabled, existing priority settings are not evaluated at query run time.

Specifies the number of CPU units allocated per segment instance. For example, if a Greenplum Database cluster has 10-core segment hosts that are configured with four segments, set the value for the segment instances to 2.5. For the master instance, the value would be 10. A master host typically has only the master instance running on it, so the value for the master should reflect the usage of all available CPU cores.

Incorrect settings can result in CPU under-utilization or query prioritization not working as designed.

Specifies the interval at which the sweeper process evaluates current CPU usage. When a new statement becomes active, its priority is evaluated and its CPU share determined when the next interval is reached.

The role of this server process " set to dispatch for the master and execute for a segment.

Specifies a minimum size for safe write operations to append-optimized tables in a non-mature file system. When a number of bytes greater than zero is specified, the append-optimized writer adds padding data up to that number in order to prevent data corruption due to file system errors. Each non-mature file system has a known safe write size that must be specified here when using Greenplum Database with that type of file system. This is commonly set to a multiple of the extent size of the file system; for example, Linux ext3 is 4096 bytes, so a value of 32768 is commonly used.

Time that the Greenplum interconnect will try to connect to a segment instance over the network before timing out. Controls the network connection timeout between master and primary segments, and primary to mirror segment replication processes.

Sets the number of primary segment instances for the Postgres Planner to assume in its cost and size estimates. If 0, then the value used is the actual number of primary segments. This variable affects the Postgres Planner's estimates of the number of rows handled by each sending and receiving process in Motion operators.

Reports the version number of the server as a string. A version modifier argument might be appended to the numeric portion of the version string, example: 5.0.0 beta.

Reports the version number of the server as an integer. The number is guaranteed to always be increasing for each version and can be used for numeric comparisons. The major version is represented as is, the minor and patch versions are zero-padded to always be double digit wide.

A system assigned ID number for a client session. Starts counting from 1 when the master instance is first started.

If enabled, when a Greenplum server process (postmaster) is started it will bind to a CPU.

Set to on to disable writes to the database. Any in progress transactions must finish before read-only mode takes affect.

Enables the use of statistics from child tables when planning queries on the parent table by the Postgres Planner.

When enabled, the Postgres Planner will use the statistics of the referenced column in the parent table when a column is foreign key reference to another table instead of the statistics of the column itself.

For a table that is defined with a DISTRIBUTED BY key_column clause, this parameter controls the hash algorithm that is used to distribute table data among segment instances. The default value is false, use the jump consistent hash algorithm.

Setting the value to true uses the modulo hash algorithm that is compatible with Greenplum Database 5.x and earlier releases.

If a database session is idle for longer than the time specified, the session will free system resources (such as shared memory), but remain connected to the database. This allows more concurrent connections to the database at one time.

Sets the amount of memory (in number of MBs) that all postgres processes of an active segment instance can consume. If a query causes this limit to be exceeded, memory will not be allocated and the query will fail. Note that this is a local parameter and must be set for every segment in the system (primary and mirrors). When setting the parameter value, specify only the numeric value. For example, to specify 4096MB, use the value 4096. Do not add the units MB to the value.

To prevent over-allocation of memory, these calculations can estimate a safe gp_vmem_protect_limit value.

gp_vmem = ((SWAP + RAM) – (7.5GB + 0.05 * RAM)) / 1.7

where SWAP is the host swap space and RAM is the RAM on the host in GB.

Next, calculate the max_acting_primary_segments. This is the maximum number of primary segments that can be running on a host when mirror segments are activated due to a failure. With mirrors arranged in a 4-host block with 8 primary segments per host, for example, a single segment host failure would activate two or three mirror segments on each remaining host in the failed host's block. The max_acting_primary_segments value for this configuration is 11 (8 primary segments plus 3 mirrors activated on failure).

This is the calculation for gp_vmem_protect_limit. The value should be converted to MB.

gp_vmem_protect_limit = gp_vmem / acting_primary_segments

For scenarios where a large number of workfiles are generated, this is the calculation for gp_vmem that accounts for the workfiles.

gp_vmem = ((SWAP + RAM) – (7.5GB + 0.05 * RAM - (300KB * total_#_workfiles))) / 1.7

For information about monitoring and managing workfile usage, see the Greenplum Database Administrator Guide.

vm.overcommit_ratio = (RAM - (0.026 * gp_vmem)) / RAM

For information about the kernel parameter, see the Greenplum Database Installation Guide.

If a query executor process consumes more than this configured amount, then the process will not be cached for use in subsequent queries after the process completes. Systems with lots of connections or idle processes may want to reduce this number to free more memory on the segments. Note that this is a local parameter and must be set for every segment.

Specifies whether the temporary files created, when a hash aggregation or hash join operation spills to disk, are compressed.

If your Greenplum Database installation uses serial ATA (SATA) disk drives, enabling compression might help to avoid overloading the disk subsystem with IO operations.

Sets the maximum number of temporary spill files (also known as workfiles) allowed per query per segment. Spill files are created when executing a query that requires more memory than it is allocated. The current query is terminated when the limit is exceeded.

Set the value to 0 (zero) to allow an unlimited number of spill files. master session reload

Sets the maximum disk size an individual query is allowed to use for creating temporary spill files at each segment. The default value is 0, which means a limit is not enforced.

Sets the maximum total disk size that all running queries are allowed to use for creating temporary spill files at each segment. The default value is 0, which means a limit is not enforced.

Sets the port on which all data collection agents communicate with the master.

Only has effect if data_checksums is enabled.

Greenplum Database uses checksums to prevent loading data that has been corrupted in the file system into memory managed by database processes.

By default, when a checksum verify error occurs when reading a heap data page, Greenplum Database generates an error and prevents the page from being loaded into managed memory. When ignore_checksum_failure is set to on and a checksum verify failure occurs, Greenplum Database generates a warning, and allows the page to be read into managed memory. If the page is then updated it is saved to disk and replicated to the mirror. If the page header is corrupt an error is reported even if this option is enabled.

The default setting is off, and it can only be changed by a superuser.

Reports whether PostgreSQL was built with support for 64-bit-integer dates and times.

Sets the display format for interval values. The value sql_standard produces output matching SQL standard interval literals. The value postgres produces output matching PostgreSQL releases prior to 8.4 when the DateStyle parameter was set to ISO.

The value postgres_verbose produces output matching Greenplum releases prior to 3.3 when the DateStyle parameter was set to non-ISO output.

The value iso_8601 will produce output matching the time interval format with designators defined in section 4.4.3.2 of ISO 8601. See the PostgreSQL 9.4 documentation for more information.

The Postgres Planner will rewrite explicit inner JOIN constructs into lists of FROM items whenever a list of no more than this many items in total would result. By default, this variable is set the same as from_collapse_limit, which is appropriate for most uses. Setting it to 1 prevents any reordering of inner JOINs. Setting this variable to a value between 1 and from_collapse_limit might be useful to trade off planning time against the quality of the chosen plan (higher values produce better plans).

Sets whether Kerberos user names should be treated case-insensitively. The default is case sensitive (off).

Sets the location of the Kerberos server key file.

Reports the locale in which sorting of textual data is done. The value is determined when the Greenplum Database array is initialized.

Reports the locale that determines character classifications. The value is determined when the Greenplum Database array is initialized.

Sets the language in which messages are displayed. The locales available depends on what was installed with your operating system - use locale -a to list available locales. The default value is inherited from the execution environment of the server. On some systems, this locale category does not exist. Setting this variable will still work, but there will be no effect. Also, there is a chance that no translated messages for the desired language exist. In that case you will continue to see the English messages.

Sets the locale to use for formatting monetary amounts, for example with the to_char family of functions. The locales available depends on what was installed with your operating system - use locale -a to list available locales. The default value is inherited from the execution environment of the server.

Sets the locale to use for formatting numbers, for example with the to_char family of functions. The locales available depends on what was installed with your operating system - use locale -a to list available locales. The default value is inherited from the execution environment of the server.

This parameter currently does nothing, but may in the future.

Specifies the TCP/IP address(es) on which the server is to listen for connections from client applications - a comma-separated list of host names and/or numeric IP addresses. The special entry * corresponds to all available IP interfaces. If the list is empty, only UNIX-domain sockets can connect.

Comma separated list of shared library files to preload at the start of a client session.

Abort any statement that waits longer than the specified number of milliseconds while attempting to acquire a lock on a table, index, row, or other database object. The time limit applies separately to each lock acquisition attempt. The limit applies both to explicit locking requests (such as LOCK TABLE, or SELECT FOR UPDATE without NOWAIT) and to implicitly-acquired locks. If log_min_error_statement is set to ERROR or lower, Greenplum Database logs the statement that timed out. A value of zero (the default) turns off this lock wait monitoring.

Unlike statement_timeout, this timeout can only occur while waiting for locks. Note that if statement_timeout is nonzero, it is rather pointless to set lock_timeout to the same or larger value, since the statement timeout would always trigger first.

Greenplum Database uses the deadlock_timeout and gp_global_deadlock_detector_period to trigger local and global deadlock detection. Note that if lock_timeout is turned on and set to a value smaller than these deadlock detection timeouts, Greenplum Database will abort a statement before it would ever trigger a deadlock check in that session.

Logs information about automatic ANALYZE operations related to gp_autostats_mode and gp_autostats_on_change_threshold.

This outputs a line to the server log detailing each successful connection. Some client programs, like psql, attempt to connect twice while determining if a password is required, so duplicate "connection received" messages do not always indicate a problem.

This outputs a line in the server log at termination of a client session, and includes the duration of the session.

When set to "on," this parameter adds a log message with verbose information about the dispatch of the statement.

Causes the duration of every completed statement which satisfies log_statement to be logged.

Controls the amount of detail written in the server log for each message that is logged.

For each query, write performance statistics of the query executor to the server log. This is a crude profiling instrument. Cannot be enabled together with log_statement_stats.

By default, connection log messages only show the IP address of the connecting host. Turning on this option causes logging of the IP address and host name of the Greenplum Database master. Note that depending on your host name resolution setup this might impose a non-negligible performance penalty.

Logs the statement and its duration on a single log line if its duration is greater than or equal to the specified number of milliseconds. Setting this to 0 will print all statements and their durations. -1 disables the feature. For example, if you set it to 250 then all SQL statements that run 250ms or longer will be logged. Enabling this option can be useful in tracking down unoptimized queries in your applications.

Controls whether or not the SQL statement that causes an error condition will also be recorded in the server log. All SQL statements that cause an error of the specified level or higher are logged. The default is PANIC (effectively turning this feature off for normal use). Enabling this option can be helpful in tracking down the source of any errors that appear in the server log.

Controls which message levels are written to the server log. Each level includes all the levels that follow it. The later the level, the fewer messages are sent to the log.

If the Greenplum Database PL/Container extension is installed. This parameter also controls the PL/Container log level. For information about the extension, see ../../analytics/pl_container.html.

For each query, write performance statistics of the query parser to the server log. This is a crude profiling instrument. Cannot be enabled together with log_statement_stats.

For each query, write performance statistics of the Postgres Planner to the server log. This is a crude profiling instrument. Cannot be enabled together with log_statement_stats.

Determines the amount of time Greenplum Database writes messages to the active log file. When this amount of time has elapsed, the file is closed and a new log file is created. Set to zero to disable time-based creation of new log files.

Determines the size of an individual log file that triggers rotation. When the log file size is equal to or greater than this size, the file is closed and a new log file is created. Set to zero to disable size-based creation of new log files.

The maximum value is INT_MAX/1024. If an invalid value is specified, the default value is used. INT_MAX is the largest value that can be stored as an integer on your system.

Controls which SQL statements are logged. DDL logs all data definition commands like CREATE, ALTER, and DROP commands. MOD logs all DDL statements, plus INSERT, UPDATE, DELETE, TRUNCATE, and COPY FROM. PREPARE and EXPLAIN ANALYZE statements are also logged if their contained command is of an appropriate type.

For each query, write total performance statistics of the query parser, planner, and executor to the server log. This is a crude profiling instrument.

Controls logging of temporary file names and sizes. Temporary files can be created for sorts, hashes, temporary query results and spill files. A log entry is made in pg_log for each temporary file when it is deleted. Depending on the source of the temporary files, the log entry could be created on either the master and/or segments. A log_temp_files value of zero logs all temporary file information, while positive values log only files whose size is greater than or equal to the specified number of kilobytes. The default setting is -1, which disables logging. Only superusers can change this setting.

Sets the time zone used for timestamps written in the log. Unlike TimeZone, this value is system-wide, so that all sessions will report timestamps consistently. The default is unknown, which means to use whatever the system environment specifies as the time zone.

Truncates (overwrites), rather than appends to, any existing log file of the same name. Truncation will occur only when a new file is being opened due to time-based rotation. For example, using this setting in combination with a log_filename such as gpseg#-%H.log would result in generating twenty-four hourly log files and then cyclically overwriting them. When off, pre-existing files will be appended to in all cases.

Specifies the maximum amount of memory to be used in maintenance operations, such as VACUUM and CREATE INDEX. It defaults to 16 megabytes (16MB). Larger settings might improve performance for vacuuming and for restoring database dumps.

Sets the maximum number of concurrent transactions that can write to or update append-optimized tables. Transactions that exceed the maximum return an error.

Operations that are counted are INSERT, UPDATE, COPY, and VACUUM operations. The limit is only for in-progress transactions. Once a transaction ends (either aborted or committed), it is no longer counted against this limit.

For operations against a partitioned table, each subpartition (child table) that is an append-optimized table and is changed counts as a single table towards the maximum. For example, a partitioned table p_tbl is defined with three subpartitions that are append-optimized tables p_tbl_ao1, p_tbl_ao2, and p_tbl_ao3. An INSERT or UPDATE command against the partitioned table p_tbl that changes append-optimized tables p_tbl_ao1 and p_tbl_ao2 is counted as two transactions.

Increasing the limit allocates more shared memory on the master host at server start.

The maximum number of concurrent connections to the database server. In a Greenplum Database system, user client connections go through the Greenplum master instance only. Segment instances should allow 5-10 times the amount as the master. When you increase this parameter, max_prepared_transactions must be increased as well. For more information about limiting concurrent connections, see "Configuring Client Authentication" in the Greenplum Database Administrator Guide.

Increasing this parameter may cause Greenplum Database to request more shared memory. Increasing this parameter might cause Greenplum Database to request more shared memory. See shared_buffers for information about Greenplum server instance shared memory buffers.

Sets the maximum number of simultaneously open files allowed to each server subprocess. If the kernel is enforcing a safe per-process limit, you don't need to worry about this setting. Some platforms such as BSD, the kernel will allow individual processes to open many more files than the system can really support.

Reports the maximum number of function arguments.

Reports the maximum identifier length.

Reports the maximum number of index keys.

The shared lock table is created with room to describe locks on max_locks_per_transaction * (max_connections + max_prepared_transactions) objects, so no more than this many distinct objects can be locked at any one time. This is not a hard limit on the number of locks taken by any one transaction, but rather a maximum average value. You might need to raise this value if you have clients that touch many different tables in a single transaction.

Sets the maximum number of transactions that can be in the prepared state simultaneously. Greenplum uses prepared transactions internally to ensure data integrity across the segments. This value must be at least as large as the value of max_connections on the master. Segment instances should be set to the same value as the master.

Sets the maximum number of simultaneously open user-declared cursors allowed per transaction. Note that an open cursor will hold an active query slot in a resource queue. Used for resource management.

Sets the maximum number of resource queues that can be created in a Greenplum Database system. Note that resource queues are system-wide (as are roles) so they apply to all databases in the system.

Specifies the maximum safe depth of the server's execution stack. The ideal setting for this parameter is the actual stack size limit enforced by the kernel (as set by ulimit -s or local equivalent), less a safety margin of a megabyte or so. Setting the parameter higher than the actual kernel limit will mean that a runaway recursive function can crash an individual backend process.

Sets the maximum memory limit for a query. Helps avoid out-of-memory errors on a segment host during query processing as a result of setting statement_mem too high.

Taking into account the configuration of a single segment host, calculate max_statement_mem as follows:

(seghost_physical_memory) / (average_number_concurrent_queries)

When changing both max_statement_mem and statement_mem, max_statement_mem must be changed first, or listed first in the postgresql.conf file.

Sets the memory usage threshold percentage for memory-intensive operators in a transaction. When a transaction reaches this threshold, it spills to disk.

The default memory_spill_ratio percentage is the value defined for the resource group assigned to the currently active role. You can set memory_spill_ratio at the session level to selectively set this limit on a per-query basis. For example, if you have a specific query that spills to disk and requires more memory, you may choose to set a larger memory_spill_ratio to increase the initial memory allocation.

You can specify an integer percentage value from 0 to 100 inclusive. If you specify a value of 0, Greenplum Database uses the statement_mem server configuration parameter value to control the initial query operator memory amount.

Enables or disables GPORCA when running SQL queries. The default is on. If you disable GPORCA, Greenplum Database uses only the Postgres Planner.

GPORCA co-exists with the Postgres Planner. With GPORCA enabled, Greenplum Database uses GPORCA to generate an execution plan for a query when possible. If GPORCA cannot be used, then the Postgres Planner is used.

The optimizer parameter can be set for a database system, an individual database, or a session or query.

For information about the Postgres Planner and GPORCA, see Querying Data.

For a partitioned table, controls whether the ROOTPARTITION keyword is required to collect root partition statistics when the ANALYZE command is run on the table. GPORCA uses the root partition statistics when generating a query plan. The Postgres Planner does not use these statistics.

The default setting for the parameter is on, the ANALYZE command can collect root partition statistics without the ROOTPARTITION keyword. Root partition statistics are collected when you run ANALYZE on the root partition, or when you run ANALYZE on a child leaf partition of the partitioned table and the other child leaf partitions have statistics. When the value is off, you must run ANALZYE ROOTPARTITION to collect root partition statistics.

When the value of the server configuration parameter optimizer is on (the default), the value of this parameter should also be on. For information about collecting table statistics on partitioned tables, see ANALYZE.

For information about the Postgres Planner and GPORCA, see Querying Data.

When GPORCA is enabled (the default) and is processing a query that contains a predicate with a constant array, the optimizer_array_expansion_threshold parameter limits the optimization process based on the number of constants in the array. If the array in the query predicate contains more than the number elements specified by parameter, GPORCA disables the transformation of the predicate into its disjunctive normal form during query optimization.

The default value is 100.

For example, when GPORCA is executing a query that contains an IN clause with more than 100 elements, GPORCA does not transform the predicate into its disjunctive normal form during query optimization to reduce optimization time consume less memory. The difference in query processing can be seen in the filter condition for the IN clause of the query EXPLAIN plan.

Changing the value of this parameter changes the trade-off between a shorter optimization time and lower memory consumption, and the potential benefits from constraint derivation during query optimization, for example conflict detection and partition elimination.

The parameter can be set for a database system, an individual database, or a session or query.

Controls whether the server configuration parameter optimizer can be changed with SET, the RESET command, or the Greenplum Database utility gpconfig. If the optimizer_control parameter value is on, users can set the optimizer parameter. If the optimizer_control parameter value is off, the optimizer parameter cannot be changed.

When GPORCA is enabled (the default), this parameter controls the amount of inlining performed for common table expression (CTE) queries (queries that contain a WHERE clause). The default value, 0, disables inlining.

The parameter can be set for a database system, an individual database, or a session or query.

When GPORCA is enabled (the default), this parameter controls whether the join associativity transform is enabled during query optimization. The transform analyzes join orders. For the default value off, only the GPORCA dynamic programming algorithm for analyzing join orders is enabled. The join associativity transform largely duplicates the functionality of the newer dynamic programming algorithm.

If the value is on, GPORCA can use the associativity transform during query optimization.

The parameter can be set for a database system, an individual database, or a session or query.

For information about GPORCA, see About GPORCA.

When GPORCA is enabled (the default) and this parameter is true (the default), GPORCA attempts to execute DML commands such as INSERT, UPDATE, and DELETE. If GPORCA cannot execute the command, Greenplum Database falls back to the Postgres Planner.

When set to false, Greenplum Database always falls back to the Postgres Planner when performing DML commands.

The parameter can be set for a database system, an individual database, or a session or query.

For information about GPORCA, see About GPORCA.

When GPORCA is enabled (the default), this parameter allows GPORCA to execute catalog queries that run only on the Greenplum Database master. For the default value off, only the Postgres Planner can execute catalog queries that run only on the Greenplum Database master.

The parameter can be set for a database system, an individual database, or a session or query.

For information about GPORCA, see About GPORCA.

When GPORCA is enabled (the default), this parameter affects the query plan alternatives that GPORCA considers when 3 stage aggregate plans are generated. When the value is true, the default, GPORCA considers only 3 stage aggregate plans where the intermediate aggregation uses the GROUP BY and DISTINCT columns for distribution to reduce the effects of processing skew.

If the value is false, GPORCA can also consider a plan that uses GROUP BY columns for distribution. These plans might perform poorly when processing skew is present.

For information about GPORCA, see About GPORCA.

For the default settings, GPORCA is enabled and this parameter is false, GPORCA makes a cost-based choice between a one- or two-stage aggregate plan for a scalar distinct qualified aggregate. When true, GPORCA chooses a multi-stage aggregate plan when such a plan alternative is generated.

The parameter can be set for a database system, an individual database, or a session or query.

For the default settings, GPORCA is enabled and this parameter is true, GPORCA chooses a plan with multistage aggregates when such a plan alternative is generated. When the value is false, GPORCA makes a cost based choice rather than a heuristic choice.

The parameter can be set for a database system, an individual database, or a session, or query.

The value is an optimization hint to limit the number of join associativity and join commutativity transformations explored during query optimization. The limit controls the alternative plans that GPORCA considers during query optimization. For example, the default value of 18 is an optimization hint for GPORCA to stop exploring join associativity and join commutativity transformations when an n-ary join operator has more than 18 children during optimization.

For a query with a large number of joins, specifying a lower value improves query performance by limiting the number of alternate query plans that GPORCA evaluates. However, setting the value too low might cause GPORCA to generate a query plan that performs sub-optimally.

This parameter has no effect when the optimizer_join_order parameter is set to query or greedy.

This parameter can be set for a database system or a session.

When GPORCA is enabled, this parameter sets the optimization level for join ordering during query optimization by specifying which types of join ordering alternatives to evaluate.

• query - Uses the join order specified in the query.
• greedy - Evaluates the join order specified in the query and alternatives based on minimum cardinalities of the relations in the joins.
• exhaustive - Applies transformation rules to find and evaluate all join ordering alternatives.

The default value is exhaustive. Setting this parameter to query or greedy can generate a suboptimal query plan. However, if the administrator is confident that a satisfactory plan is generated with the query or greedy setting, query optimization time can be improved by setting the parameter to the lower optimization level.

Setting this parameter to query or greedy overrides the optimizer_join_order_threshold and optimizer_join_arity_for_associativity_commutativity parameters.

This parameter can be set for an individual database, a session, or a query.

When GPORCA is enabled (the default), this parameter sets the maximum number of join children for which GPORCA will use the dynamic programming-based join ordering algorithm. You can set this value for a single query or for an entire session.

This parameter has no effect when the optimizer_join_query parameter is set to query or greedy.

Sets the maximum amount of memory on the Greenplum Database master that GPORCA uses to cache query metadata (optimization data) during query optimization. The memory limit session based. GPORCA caches query metadata during query optimization with the default settings: GPORCA is enabled and optimizer_metadata_caching is on.

The default value is 16384 (16MB). This is an optimal value that has been determined through performance analysis.

You can specify a value in KB, MB, or GB. The default unit is KB. For example, a value of 16384 is 16384KB. A value of 1GB is the same as 1024MB or 1048576KB. If the value is 0, the size of the cache is not limited.

This parameter can be set for a database system, an individual database, or a session or query.

When GPORCA is enabled (the default), this parameter specifies whether GPORCA caches query metadata (optimization data) in memory on the Greenplum Database master during query optimization. The default for this parameter is on, enable caching. The cache is session based. When a session ends, the cache is released. If the amount of query metadata exceeds the cache size, then old, unused metadata is evicted from the cache.

If the value is off, GPORCA does not cache metadata during query optimization.

This parameter can be set for a database system, an individual database, or a session or query.

The server configuration parameter optimizer_mdcache_size controls the size of the query metadata cache.

GPORCA generates minidump files to describe the optimization context for a given query. The information in the file is not in a format that can be easily used for debugging or troubleshooting. The minidump file is located under the master data directory and uses the following naming format:

Minidump_date_time.mdp

Setting this parameter to ALWAYS generates a minidump for all queries. Set this parameter to ONERROR to minimize total optimization time.

For information about GPORCA, see About GPORCA.

This parameter adds a costing factor to GPORCA to prioritize hash joins instead of nested loop joins during query optimization. The default value of 1024 was chosen after evaluating numerous workloads with uniformly distributed data. 1024 should be treated as the practical upper bound setting for this parameter. If you find the GPORCA selects hash joins more often than it should, reduce the value to shift the costing factor in favor of nested loop joins.

The parameter can be set for a database system, an individual database, or a session or query.

When GPORCA is enabled (the default), optimizer_parallel_union controls the amount of parallelization that occurs for queries that contain a UNION or UNION ALL clause.

When the value is off, the default, GPORCA generates a query plan where each child of an APPEND(UNION) operator is in the same slice as the APPEND operator. During query execution, the children are executed in a sequential manner.

When the value is on, GPORCA generates a query plan where a redistribution motion node is under an APPEND(UNION) operator. During query execution, the children and the parent APPEND operator are on different slices, allowing the children of the APPEND(UNION) operator to execute in parallel on segment instances.

The parameter can be set for a database system, an individual database, or a session or query.

When GPORCA is enabled (the default), this parameter allows GPORCA to penalize the local cost of a HashJoin with a skewed Redistribute Motion as child to favor a Broadcast Motion during query optimization. The default value is true.

GPORCA determines there is skew for a Redistribute Motion when the NDV (number of distinct values) is less than the number of segments.

The parameter can be set for a database system, an individual database, or a session or query.

For information about GPORCA, see About GPORCA.

When GPORCA is enabled (the default), this parameter controls the display of table column information about columns with missing statistics for a query. The default value is true, display the column information to the client. When the value is false, the information is not sent to the client.

The information is displayed during query execution, or with the EXPLAIN or EXPLAIN ANALYZE commands.

The parameter can be set for a database system, an individual database, or a session.

The information is logged during query execution, or with the EXPLAIN or EXPLAIN ANALYZE commands.

This parameter can be set for a database system, an individual database, or a session or query.

When GPORCA is enabled (the default), optimizer_sort_factor controls the cost factor to apply to sorting operations during query optimization. The default value 1 specifies the default sort cost factor. The value is a ratio of increase or decrease from the default factor. For example, a value of 2.0 sets the cost factor at twice the default, and a value of 0.5 sets the factor at half the default.

The parameter can be set for a database system, an individual database, or a session or query.

When GPORCA is enabled (the default) and this parameter is true (the default), GPORCA uses Greenplum Database memory management when executing queries. When set to false, GPORCA uses GPORCA-specific memory management. Greenplum Database memory management allows for faster optimization, reduced memory usage during optimization, and improves GPORCA support of vmem limits when compared to GPORCA-specific memory management.

For information about GPORCA, see About GPORCA.

When a password is specified in CREATE USER or ALTER USER without writing either ENCRYPTED or UNENCRYPTED, this option determines whether the password is to be encrypted.

Specifies the cryptographic hash algorithm that is used when storing an encrypted Greenplum Database user password. The default algorithm is MD5.

For information about setting the password hash algorithm to protect user passwords, see "Protecting Passwords in Greenplum Database" in the Greenplum Database Administrator Guide.

A colon (:) separated list of jar files or directories containing jar files needed for PL/Java functions. The full path to the jar file or directory must be specified, except the path can be omitted for jar files in the $GPHOME/lib/postgresql/java directory. The jar files must be installed in the same locations on all Greenplum hosts and readable by the gpadmin user.

The pljava_classpath parameter is used to assemble the PL/Java classpath at the beginning of each user session. Jar files added after a session has started are not available to that session.

If the full path to a jar file is specified in pljava_classpath it is added to the PL/Java classpath. When a directory is specified, any jar files the directory contains are added to the PL/Java classpath. The search does not descend into subdirectories of the specified directories. If the name of a jar file is included in pljava_classpath with no path, the jar file must be in the $GPHOME/lib/postgresql/java directory.

If pljava_classpath_insecure is false, setting the pljava_classpath parameter requires superuser privilege. Setting the classpath in SQL code will fail when the code is executed by a user without superuser privilege. The pljava_classpath parameter must have been set previously by a superuser or in the postgresql.conf file. Changing the classpath in the postgresql.conf file requires a reload (gpstop -u).

Controls whether the server configuration parameter pljava_classpath can be set by a user without Greenplum Database superuser privileges. When true, pljava_classpath can be set by a regular user. Otherwise, pljava_classpath can be set only by a database superuser. The default is false.

Sets the size in KB of the JRE MRU (Most Recently Used) cache for prepared statements.

If true, lingering savepoints used in PL/Java functions will be released on function exit. If false, savepoints will be rolled back.

Defines the startup options for the Java VM. The default value is an empty string ("").

The database listener port for a Greenplum instance. The master and each segment has its own port. Port numbers for the Greenplum system must also be changed in the gp_segment_configuration catalog. You must shut down your Greenplum Database system before changing port numbers.

Sets the estimate of the cost of a nonsequentially fetched disk page for the Postgres Planner. This is measured as a multiple of the cost of a sequential page fetch. A higher value makes it more likely a sequential scan will be used, a lower value makes it more likely an index scan will be used.

When an SQL query reads from an external table, the parameter value specifies the amount of time in seconds that Greenplum Database waits before cancelling the query when data stops being returned from the external table.

The default value of 0, specifies no time out. Greenplum Database does not cancel the query.

If queries that use gpfdist run a long time and then return the error "intermittent network connectivity issues", you can specify a value for readable_external_table_timeout. If no data is returned by gpfdist for the specified length of time, Greenplum Database cancels the query.

For Greenplum Database master mirroring, controls updates to the active master. If the number of WAL segment files that have not been processed by the walsender exceeds this value, Greenplum Database updates the active master.

If the number of segment files does not exceed the value, Greenplum Database blocks updates to the to allow the walsender process the files. If all WAL segments have been processed, the active master is updated.

For Greenplum Database master mirroring, sets the maximum time in milliseconds that the walsender process on the active master waits for a status message from the walreceiver process on the standby master. If a message is not received, the walsender logs an error message.

The wal_receiver_status_interval controls the interval between walreceiver status messages.

The 'extended' setting may be useful for exact backwards compatibility with pre-7.4 releases of PostgreSQL.

If a statement is submitted through a resource queue, clean up any idle query executor worker processes before taking a lock on the resource queue.

Sets the types of queries managed by resource queues. If set to on, then SELECT, SELECT INTO, CREATE TABLE AS SELECT, and DECLARE CURSOR commands are evaluated. If set to off INSERT, UPDATE, and DELETE commands will be evaluated as well.

Sets the percentage of Greenplum Database vmem memory that triggers the termination of queries. If the percentage of vmem memory that is utilized for a Greenplum Database segment exceeds the specified value, Greenplum Database terminates queries based on memory usage, starting with the query consuming the largest amount of memory. Queries are terminated until the percentage of utilized vmem is below the specified percentage.

Specify the maximum vmem value for active Greenplum Database segment instances with the server configuration parameter gp_vmem_protect_limit.

For example, if vmem memory is set to 10GB, and the value of runaway_detector_activation_percent is 90 (90%), Greenplum Database starts terminating queries when the utilized vmem memory exceeds 9 GB.

A value of 0 disables the automatic termination of queries based on percentage of vmem that is utilized.

Specifies the order in which schemas are searched when an object is referenced by a simple name with no schema component. When there are objects of identical names in different schemas, the one found first in the search path is used. The system catalog schema, pg_catalog, is always searched, whether it is mentioned in the path or not. When objects are created without specifying a particular target schema, they will be placed in the first schema listed in the search path. The current effective value of the search path can be examined via the SQL function current_schemas(). current_schemas() shows how the requests appearing in search_path were resolved.

For the Postgres Planner, sets the estimate of the cost of a disk page fetch that is part of a series of sequential fetches.

Reports the database encoding (character set). It is determined when the Greenplum Database array is initialized. Ordinarily, clients need only be concerned with the value of client_encoding.

Reports the version of PostgreSQL that this release of Greenplum Database is based on.

Reports the version of PostgreSQL that this release of Greenplum Database is based on as an integer.

Sets the amount of memory a Greenplum Database segment instance uses for shared memory buffers. This setting must be at least 128KB and at least 16KB times max_connections.

Each Greenplum Database segment instance calculates and attempts to allocate certain amount of shared memory based on the segment configuration. The value of shared_buffers is significant portion of this shared memory calculation, but is not all it. When setting shared_buffers, the values for the operating system parameters SHMMAX or SHMALL might also need to be adjusted.

 shared_buffers + other_seg_shmem

With the default Greenplum Database parameter values, the value for other_seg_shmem is approximately 111MB for Greenplum Database segments and approximately 79MB for the Greenplum Database master.

 (num_instances_per_host * ( shared_buffers + other_seg_shmem )) + other_app_shared_mem 

When shared memory allocation errors occur, possible ways to resolve shared memory allocation issues are to increase SHMMAX or SHMALL, or decrease shared_buffers or max_connections.

See the Greenplum Database Installation Guide for information about the Greenplum Database values for the parameters SHMMAX and SHMALL.

A comma-separated list of shared libraries that are to be preloaded at server start. PostgreSQL procedural language libraries can be preloaded in this way, typically by using the syntax '$libdir/plXXX' where XXX is pgsql, perl, tcl, or python. By preloading a shared library, the library startup time is avoided when the library is first used. If a specified library is not found, the server will fail to start.

Enables SSL connections.

Specifies a list of SSL ciphers that are allowed to be used on secure connections. See the openssl manual page for a list of supported ciphers.

Determines whether ordinary string literals ('...') treat backslashes literally, as specified in the SQL standard. The default value is on. Turn this parameter off to treat backslashes in string literals as escape characters instead of literal backslashes. Applications may check this parameter to determine how string literals are processed. The presence of this parameter can also be taken as an indication that the escape string syntax (E'...') is supported.

Allocates segment host memory per query. The amount of memory allocated with this parameter cannot exceed max_statement_mem or the memory limit on the resource queue or resource group through which the query was submitted. If additional memory is required for a query, temporary spill files on disk are used.

If you are using resource groups to control resource allocation in your Greenplum Database cluster:

• Greenplum Database uses statement_mem to control query memory usage when the resource group MEMORY_SPILL_RATIO is set to 0.
• You can use the following calculation to estimate a reasonable statement_mem value:

  rg_perseg_mem = ((RAM * (vm.overcommit_ratio / 100) + SWAP) * gp_resource_group_memory_limit) / num_active_primary_segments
  statement_mem = rg_perseg_mem / max_expected_concurrent_queries

If you are using resource queues to control resource allocation in your Greenplum Database cluster:

• When gp_resqueue_memory_policy =auto, statement_mem and resource queue memory limits control query memory usage.
• You can use the following calculation to estimate a reasonable statement_mem value for a wide variety of situations:

  ( gp_vmem_protect_limitGB * .9 ) / max_expected_concurrent_queries

  For example, with a gp_vmem_protect_limit set to 8192MB (8GB) and assuming a maximum of 40 concurrent queries with a 10% buffer, you would use the following calculation to determine the statement_mem value:

  (8GB * .9) / 40 = .18GB = 184MB

When changing both max_statement_mem and statement_mem, max_statement_mem must be changed first, or listed first in the postgresql.conf file.

Abort any statement that takes over the specified number of milliseconds. 0 turns off the limitation.

Collects resource queue statistics on database activity.

Determines the number of connection slots that are reserved for Greenplum Database superusers.

How many keepalives may be lost before the connection is considered dead. A value of 0 uses the system default. If TCP_KEEPCNT is not supported, this parameter must be 0.

Use this parameter for all connections that are not between a primary and mirror segment.

Number of seconds between sending keepalives on an otherwise idle connection. A value of 0 uses the system default. If TCP_KEEPIDLE is not supported, this parameter must be 0.

Use this parameter for all connections that are not between a primary and mirror segment.

How many seconds to wait for a response to a keepalive before retransmitting. A value of 0 uses the system default. If TCP_KEEPINTVL is not supported, this parameter must be 0.

Use this parameter for all connections that are not between a primary and mirror segment.

Sets the maximum memory, in blocks, to allow for temporary buffers by each database session. These are session-local buffers used only for access to temporary tables. The setting can be changed within individual sessions, but only up until the first use of temporary tables within a session. The cost of setting a large value in sessions that do not actually need a lot of temporary buffers is only a buffer descriptor for each block, or about 64 bytes, per increment. However if a buffer is actually used, an additional 32768 bytes will be consumed.

You can set this parameter to the number of 32K blocks (for example, 1024 to allow 32MB for buffers), or specify the maximum amount of memory to allow (for example '48MB' for 1536 blocks). The gpconfig utility and SHOW command report the maximum amount of memory allowed for temporary buffers.

Specifies tablespaces in which to create temporary objects (temp tables and indexes on temp tables) when a CREATE command does not explicitly specify a tablespace. Temporary files for purposes such as sorting large data sets are also created in these tablespaces.

The value is a comma-separated list of names of tablespaces. When there is more than one name in the list, Greenplum chooses a random member of the list each time a temporary object is to be created; except that within a transaction, successively created temporary objects are placed in successive tablespaces from the list. If the selected element of the list is an empty string, Greenplum automatically uses the default tablespace of the current database instead.

When temp_tablespaces is set interactively, specifying a nonexistent tablespace is an error, as is specifying a tablespace for which the user does not have CREATE privilege. However, when using a previously set value, nonexistent tablespaces are ignored, as are tablespaces for which the user lacks CREATE privilege. In particular, this rule applies when using a value set in postgresql.conf.

The default value is an empty string, which results in all temporary objects being created in the default tablespace of the current database.

See also default_tablespace.

Sets the time zone for displaying and interpreting time stamps. The default is to use whatever the system environment specifies as the time zone. See Date/Time Keywords in the PostgreSQL documentation.

Sets the collection of time zone abbreviations that will be accepted by the server for date time input. The default is Default, which is a collection that works in most of the world. Australia and India, and other collections can be defined for a particular installation. Possible values are names of configuration files stored in $GPHOME/share/postgresql/timezonesets/.

To configure Greenplum Database to use a custom collection of timezones, copy the file that contains the timezone definitions to the directory $GPHOME/share/postgresql/timezonesets/ on the Greenplum Database master and segment hosts. Then set value of the server configuration parameter timezone_abbreviations to the file. For example, to use a file custom that contains the default timezones and the WIB (Waktu Indonesia Barat) timezone.

1. Copy the file Default from the directory $GPHOME/share/postgresql/timezonesets/ the file custom. Add the WIB timezone information from the file Asia.txt to the custom.
2. Copy the file custom to the directory $GPHOME/share/postgresql/timezonesets/ on the Greenplum Database master and segment hosts.
3. Set value of the server configuration parameter timezone_abbreviations to custom.
4. Reload the server configuration file (gpstop -u).

Sets the maximum length limit for the query text stored in query column of the system catalog view pg_stat_activity. The minimum length is 1024 characters.

Sets the current transaction's isolation level.

Sets the current transaction's read-only status.

When on, expressions of the form expr = NULL (or NULL = expr) are treated as expr IS NULL, that is, they return true if expr evaluates to the null value, and false otherwise. The correct SQL-spec-compliant behavior of expr = NULL is to always return null (unknown).

Specifies the directory of the UNIX-domain socket on which the server is to listen for connections from client applications.

Sets the owning group of the UNIX-domain socket. By default this is an empty string, which uses the default group for the current user.

Sets the access permissions of the UNIX-domain socket. UNIX-domain sockets use the usual UNIX file system permission set. Note that for a UNIX-domain socket, only write permission matters.

Enables updating of the process title every time a new SQL command is received by the server. The process title is typically viewed by the ps command.

The length of time that the process will sleep when the cost limit has been exceeded. 0 disables the cost-based vacuum delay feature.

The accumulated cost that will cause the vacuuming process to sleep.

The estimated cost charged when vacuum modifies a block that was previously clean. It represents the extra I/O required to flush the dirty block out to disk again.

The estimated cost for vacuuming a buffer found in the shared buffer cache. It represents the cost to lock the buffer pool, lookup the shared hash table and scan the content of the page.

The estimated cost for vacuuming a buffer that has to be read from disk. This represents the effort to lock the buffer pool, lookup the shared hash table, read the desired block in from the disk and scan its content.

Specifies the cutoff age (in transactions) that VACUUM should use to decide whether to replace transaction IDs with FrozenXID while scanning a table.

For information about VACUUM and transaction ID management, see "Managing Data" in the Greenplum Database Administrator Guide and the PostgreSQL documentation.

Enables a test that validates the free tuple ID (TID) list. The list is maintained and used by Greenplum Database. Greenplum Database determines the validity of the free TID list by ensuring the previous free TID of the current free tuple is a valid free tuple. The default value is true, enable the test.

If Greenplum Database detects a corruption in the free TID list, the free TID list is rebuilt, a warning is logged, and a warning is returned by queries for which the check failed. Greenplum Database attempts to execute the queries.

When a Greenplum Database external table is defined with the gpfdists protocol to use SSL security, this parameter controls whether SSL certificate authentication is enabled. The default is true, SSL authentication is enabled when Greenplum Database communicates with the gpfdist utility to either read data from or write data to an external data source.

For information about the gpfdists protocol, see gpfdists:// Protocol. For information about running the gpfdist utility, see gpfdist.

Enables checking for interrupts before reserving vmem memory for a query during Greenplum Database query execution. Before reserving further vmem for a query, check if the current session for the query has a pending query cancellation or other pending interrupts. This ensures more responsive interrupt processing, including query cancellation requests. The default is off.

When Greenplum Database segment mirroring is enabled, specifies the maximum amount of Write-Ahead Logging (WAL)-based records (in KB) written by a transaction on the primary segment instance before the records are written to the mirror segment instance for replication. As the default, Greenplum Database writes the records to the mirror segment instance when a checkpoint occurs or the wait_for_replication_threshold value is reached.

A value of 0 disables the check for the amount of records. The records are written to the mirror segment instance only after a checkpoint occurs.

If you set the value to 0, database performance issues might occur under heavy loads that perform long transactions that do not perform a checkpoint operation.

For Greenplum Database master mirroring, sets the maximum number of processed WAL segment files that are saved by the by the active Greenplum Database master if a checkpoint operation occurs.

The segment files are used to synchronize the active master on the standby master.

For Greenplum Database master mirroring, sets the interval in seconds between walreceiver process status messages that are sent to the active master. Under heavy loads, the time might be longer.

The value of replication_timeout controls the time that the walsender process waits for a walreceiver message.

Size of the buffer (in KB) that Greenplum Database uses for network communication, such as the gpfdist utility and external web tables (that use http). Greenplum Database stores data in the buffer before writing the data out. For information about gpfdist, see the Greenplum Database Utility Guide.

The number of transaction IDs prior to the ID where transaction ID wraparound occurs. When this limit is reached, Greenplum Database stops creating new transactions to avoid data loss due to transaction ID wraparound.

The number of transaction IDs prior to the limit specified by xid_stop_limit. When Greenplum Database reaches this limit, it issues a warning to perform a VACUUM operation to avoid data loss due to transaction ID wraparound.

Specifies how binary values are encoded in XML data. For example, when bytea values are converted to XML. The binary data can be converted to either base64 encoding or hexadecimal encoding. The default is base64.

The parameter can be set for a database system, an individual database, or a session.

Specifies whether XML data is to be considered as an XML document (document) or XML content fragment (content) for operations that perform implicit parsing and serialization. The default is content.

This parameter affects the validation performed by xml_is_well_formed(). If the value is document, the function checks for a well-formed XML document. If the value is content, the function checks for a well-formed XML content fragment.

SET XML OPTION { DOCUMENT | CONTENT }