Example: Merging Data from Kafka into Greenplum Using gpsscli

In this example, you merge data from a Kafka topic named customer_orders into a Greenplum Database table named customer_orders_tbl. You perform the operation as the Greenplum role gpadmin. The table customer_orders_tbl resides in the public schema in a Greenplum database named testdb.

A producer of the Kafka customer_orders topic emits customer order messages in CSV format that include the customer identifier (integer) and an order amount (decimal). For example, a message for a customer with identifier 123 who spent $456.78 follows:

"123","456.78"

You will run a Kafka console producer to emit customer order messages, start a Greenplum Streaming Server instance, and use the GPSS gpsscli subcommands to merge and load the data into the customer_orders_tbl Greenplum table. This table has pre-existing data that the merge will overwrite.

Prerequisites

Before you start this procedure, ensure that you:

Have administrative access to run Kafka and Greenplum Database clusters.
Have configured connectivity as described in both the Greenplum Streaming Server Prerequisites section and the Kafka Prerequisites.
Identify and note the ZooKeeper hostname and port.
Identify and note the hostname and port of the Kafka broker(s).
Identify and note the hostname and port of the Greenplum Database master node.
Register the GPSS extension.

This procedure assumes that you have installed the Apache Kafka distribution. If you are using a different Kafka distribution, you may need to adjust certain commands in the procedure.

Procedure

Create a Kafka topic named customer_orders. For example:

kafkahost$ $KAFKA_INSTALL_DIR/bin/kafka-topics.sh --create \
    --zookeeper localhost:2181 --replication-factor 1 --partitions 1 \
    --topic customer_orders

Open a file named sample_customer_data.csv in the editor of your choice. For example:
```
kafkahost$ vi sample_customer_data.csv
```
Copy/paste the following text to add CSV-format data into the file, and then save and exit:
```
"1313131","1000.00"
"4444444","99.13"
"1515151","500.05"
"6666666","1.12"
"1717171","3000.03"
```

Stream the contents of the sample_customer_data.csv file to a Kafka console producer. For example:

kafkahost$ $KAFKA_INSTALL_DIR/bin/kafka-console-producer.sh \
    --broker-list localhost:9092 \
    --topic customer_orders < sample_customer_data.csv

Run the Kafka console consumer to verify that the Kafka console producer published the messages to the topic. For example:

kafkahost$ $KAFKA_INSTALL_DIR/bin/kafka-console-consumer.sh \
    --bootstrap-server localhost:9092 --topic customer_orders \
    --from-beginning

Open a new terminal window, log in to the Greenplum Database master host as the gpadmin administrative user, and set up the Greenplum environment. For example:
```
$ ssh gpadmin@gpmaster
gpmaster$ . /usr/local/greenplum-db/greenplum_path.sh
```
Construct the the Greenplum Streaming Server configuration file. For example, open a file named gpsscfg_ex.json in the editor of your choice:
```
gpmaster$ vi gpsscfg_ex.json
```
Designate a GPSS listen port number of 5019 and a gpfdist port number of 8319 in the configuration file. For example, copy/paste the following into the gpsscfg_ex.json file, and then save and exit the editor:
```
{
    "ListenAddress": {
        "Host": "",
        "Port": 5019
    },
    "Gpfdist": {
        "Host": "",
        "Port": 8319
    }
}
```
Start the Greenplum Streaming Server instance in the background, specifying the log directory ./gpsslogs. For example:
```
gpmaster$ gpss gpsscfg_ex.json --log-dir ./gpsslogs & 
```
Construct the gpkafka load configuration file. Open a file named custorders_cfg.yaml in the editor of your choice. For example:
```
gpmaster$ vi custorders_cfg.yaml
```
Fill in the load configuration parameter values based on your environment. This example assumes:
- Your Greenplum Database master hostname is gpmaster.
- The Greenplum Database server is running on the default port.
- Your Kafka broker host and port is localhost:9092.
- You want to write the Kafka data to a Greenplum Database table named customer_orders_tbl located in the public schema of a database named testdb.
- You want to write the customer identifier and order data to Greenplum. If the customer is already present in the table, replace the order amount with the amount read from Kafka. If the customer is not present in the table, add the customer identifier and order amount. You will set merge- and update-related properties in the file to reflect this.
The custorders_cfg.yaml file would include the following contents:
```
DATABASE: testdb
USER: gpadmin
HOST: gpmaster
PORT: 5432
KAFKA:
   INPUT:
      SOURCE:
        BROKERS: localhost:9092
        TOPIC: customer_orders
      COLUMNS:
        - NAME: id
          TYPE: int
        - NAME: order_amount
          TYPE: decimal(9,2)
      FORMAT: csv
      ERROR_LIMIT: 25
   OUTPUT:
      TABLE: customer_orders_tbl
      MODE: MERGE
      MATCH_COLUMNS:
        - id
      UPDATE_COLUMNS:
        - amount
      MAPPING:
        - NAME: id
          EXPRESSION: id
        - NAME: amount
          EXPRESSION: order_amount
   COMMIT:
      MINIMAL_INTERVAL: 2000
```
Start the psql subsystem:
```
gpmaster$ psql -d testdb
testdb=#
```

Create the target Greenplum Database table named customer_orders_tbl, and insert two rows of data in the table. For example:

CREATE TABLE customer_orders_tbl( id int8, amount decimal(9,2) );
INSERT INTO customer_orders_tbl VALUES (1717171, 17.17);
INSERT INTO customer_orders_tbl VALUES (1515151, 15.15);

Exit the psql subsystem:
```
testdb=# \q
```
Submit the Kafka data load job to the GPSS instance running on port number 5019. (You may consider opening a new terminal window to run the command.) For example to submit a job named orders1:
```
gpmaster$ gpsscli submit --name orders1 --gpss-port 5019 ./custorders_cfg.yaml
20200804 12:54:19.25262,116652,info,JobID: d577cf37890b5b6bf4e713a9586e86c9,JobName: orders1
```

List all GPSS jobs. For example:

gpmaster$ gpsscli list --all --gpss-port 5019
JobName          JobID                               GPHost       GPPort   DataBase    Schema      Table                  Topic            Status
orders1          d577cf37890b5b6bf4e713a9586e86c9    localhost    5432     testdb      public      customer_orders_tbl    customer_orders  JOB_STOPPED

The list subcommand displays all jobs. Notice the entry for the orders1 job that you just submitted, and that the job is in the Stopped state.

Start the job named orders1. For example:

gpmaster$ gpsscli start orders1 --gpss-port 5019
20200804 12:57:57.35153,117918,info,Job orders1 is started

Stop the job named orders1. For example:

gpmaster$ gpsscli stop orders1 --gpss-port 5019
20200804 13:05:09.24280,117506,info,stop job: orders1 success

Examine the gpss command output and log file, looking for messages that identify the number of rows inserted/rejected. For example:
```
... -[INFO]:- ... Inserted 5 rows
... -[INFO]:- ... Rejected 0 rows
```
View the contents of the Greenplum Database target table customer_orders_tbl:
```
gpmaster$ psql -d testdb

SELECT * FROM customer_orders_tbl ORDER BY id;
   id    | amount  
---------+---------
 1313131 | 1000.00
 1515151 |  500.05
 1717171 | 3000.03
 4444444 |   99.13
 6666666 |    1.12
(5 rows)
```
Notice that the amount value for customers with ids 1515151 and 1717171 have been updated to the total_amount read from the Kafka message.