pageinspect

pageinspect

The pageinspect module provides functions for low level inspection of the contents of database pages. pageinspect is available only to Greenplum Database superusers.

The Greenplum Database pageinspect module is based on the PostgreSQL pageinspect module. The Greenplum version of the module differs as described in the Greenplum Database Considerations topic.

Installing and Registering the Module

The pageinspect module is installed when you install Greenplum Database. Before you can use any of the functions defined in the module, you must register the pageinspect extension in each database in which you want to use the functions:

CREATE EXTENSION pageinspect;

Refer to Installing Additional Supplied Modules for more information.

Upgrading the Module

If you are currently using pageinspect in your Greenplum installation and you want to access newly-released module functionality, you must update the pageinspect extension in every database in which it is currently registered:

ALTER EXTENSION pageinspect UPDATE;

Module Documentation

See pageinspect in the PostgreSQL documentation for detailed information about the majority of functions in this module.

The next topic includes documentation for Greenplum-added pageinspect functions.

Greenplum Database Considerations

When using this module with Greenplum Database, consider the following:

  • The Greenplum Database version of the pageinspect does not allow inspection of pages belonging to append-optimized or external relations.
  • For pageinspect functions that read data from a database, the function reads data only from the segment instance where the function is run. For example, the get_raw_page() function returns a block number out of range error when you try to read data from a user-defined table on the Greenplum Database master because there is no data in the table on the master segment. The function will read data from a system catalog table on the master segment.

Greenplum-Added Functions

In addition to the functions specified in the PostgreSQL documentation, Greenplum Database provides these additional pageinspect functions for inspecting bitmap index pages:

Function Name Description
bm_metap(relname text) returns record Returns information about a bitmap index's meta page.
bm_bitmap_page_header(relname text, blkno int) returns record Returns the header information for a bitmap page; this corresponds to the opaque section from the page header.
bm_lov_page_items(relname text, blkno int) returns setof record Returns the list of value (LOV) items present in a bitmap LOV page.
bm_bitmap_page_items(relname text, blkno int) returns setof record Returns the content words and their compression statuses for a bitmap page.
bm_bitmap_page_items(page bytea) returns setof record Returns the content words and their compression statuses for a page image obtained by get_raw_page().

Examples

Greenplum-added pageinspect function usage examples follow.

Obtain information about the meta page of the bitmap index named i1:

testdb=# SELECT * FROM bm_metap('i1');
   magic    | version | auxrelid | auxindexrelid | lovlastblknum
------------+---------+----------+---------------+---------------
 1112101965 |       2 |   169980 |        169982 |             1
(1 row)

Display the header information for the second block of the bitmap index named i1:

testdb=# SELECT * FROM bm_bitmap_page_header('i1', 2);
 num_words | next_blkno | last_tid 
-----------+------------+----------
 3         | 4294967295 | 65536    
(1 row)

Display the LOV items located in the first block of the bitmap index named i1:

testdb=# SELECT * FROM bm_lov_page_items('i1', 1) ORDER BY itemoffset;
 itemoffset | lov_head_blkno | lov_tail_blkno | last_complete_word      | last_word               | last_tid | last_setbit_tid | is_last_complete_word_fill | is_last_word_fill 
------------+----------------+----------------+-------------------------+-------------------------+----------+-----------------+----------------------------+-------------------
 1          | 4294967295     | 4294967295     | ff ff ff ff ff ff ff ff | 00 00 00 00 00 00 00 00 | 0        | 0               | f                          | f                 
 2          | 2              | 2              | 80 00 00 00 00 00 00 01 | 00 00 00 00 07 ff ff ff | 65600    | 65627           | t                          | f                 
 3          | 3              | 3              | 80 00 00 00 00 00 00 02 | 00 3f ff ff ff ff ff ff | 131200   | 131254          | t                          | f                 
(3 rows)

Return the content words located in the second block of the bitmap index named i1:

testdb=# SELECT * FROM bm_bitmap_page_items('i1', 2) ORDER BY word_num;
 word_num | compressed | content_word            
----------+------------+-------------------------
 0        | t          | 80 00 00 00 00 00 00 0e 
 1        | f          | 00 00 00 00 00 00 1f ff 
 2        | t          | 00 00 00 00 00 00 03 f1 
(3 rows)

Alternatively, return the content words located in the heap page image of the same bitmap index and block:

testdb=# SELECT * FROM bm_bitmap_page_items(get_raw_page('i1', 2)) ORDER BY word_num;
 word_num | compressed | content_word            
----------+------------+-------------------------
 0        | t          | 80 00 00 00 00 00 00 0e 
 1        | f          | 00 00 00 00 00 00 1f ff 
 2        | t          | 00 00 00 00 00 00 03 f1 
(3 rows)