Example: Loading JSON Data from Kafka Using the Streaming Server

Note: This example is similar to an example in the Greenplum-Kafka Integration documentation, but it uses the Greenplum Streaming Server client utility, gpsscli, rather than the gpkafka utility, to load JSON-format data from Kafka into Greenplum Database.

In this example, you load JSON format data from a Kafka topic named topic_json_gpkafka into a Greenplum Database table named json_from_kafka. You perform the load as the Greenplum role gpadmin. The table json_from_kafka resides in the public schema in a Greenplum database named testdb.

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

{ "cust_id": 123, "month": 9, "amount_paid":456.78 }

You will run a Kafka console producer to emit JSON-format customer expense messages, start a Greenplum Streaming Server instance, and use the GPSS gpsscli subcommands to load the data into the json_from_kafka table.

Prerequisites

Before you start this procedure, ensure that you:

Have administrative access to running Kafka and Greenplum Database clusters.
Have configured connectivity as described in both the Greenplum Streaming Server Prerequisites section and the Prerequisites section in the Greenplum-Kafka Integration documentation.
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 topic_json_gpkafka. For example:

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

Open a file named sample_data.json in the editor of your choice. For example:
```
kafkahost$ vi sample_data.json
```

Copy/paste the following text to add JSON-format data into the file, and then save and exit:

{ "cust_id": 1313131, "month": 12, "expenses": 1313.13 }
{ "cust_id": 3535353, "month": 11, "expenses": 761.35 }
{ "cust_id": 7979797, "month": 10, "expenses": 4489.00 }
{ "cust_id": 7979797, "month": 11, "expenses": 18.72 }
{ "cust_id": 3535353, "month": 10, "expenses": 6001.94 }
{ "cust_id": 7979797, "month": 12, "expenses": 173.18 }
{ "cust_id": 1313131, "month": 10, "expenses": 492.83 }
{ "cust_id": 3535353, "month": 12, "expenses": 81.12 }
{ "cust_id": 1313131, "month": 11, "expenses": 368.27 }

Stream the contents of the sample_data.json file to a Kafka console producer. For example:

kafkahost$ $KAFKA_INSTALL_DIR/bin/kafka-console-producer.sh \
    --broker-list localhost:9092 \
    --topic topic_json_gpkafka < sample_data.json

Verify that the Kafka console producer published the messages to the topic by running a Kafka console consumer. For example:

kafkahost$ $KAFKA_INSTALL_DIR/bin/kafka-console-consumer.sh \
    --bootstrap-server localhost:9092 --topic topic_json_gpkafka \
    --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 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 50007 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": 50007
    },
    "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 jsonload_cfg.yaml in the editor of your choice. For example:
```
gpmaster$ vi jsonload_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 json_from_kafka located in the public schema of a database named testdb.
You want to write the customer identifier and expenses data to Greenplum.

The jsonload_cfg.yaml file would include the following contents:

DATABASE: testdb
USER: gpadmin
HOST: gpmaster
PORT: 5432
KAFKA:
   INPUT:
     SOURCE:
        BROKERS: localhost:9092
        TOPIC: topic_json_gpkafka
     COLUMNS:
        - NAME: jdata
          TYPE: json
     FORMAT: json
     ERROR_LIMIT: 10
   OUTPUT:
     TABLE: json_from_kafka
     MAPPING:
        - NAME: customer_id
          EXPRESSION: (jdata->>'cust_id')::int
        - NAME: month
          EXPRESSION: (jdata->>'month')::int
        - NAME: amount_paid
          EXPRESSION: (jdata->>'expenses')::decimal
   COMMIT:
     MINIMAL_INTERVAL: 2000

Create the target Greenplum Database table named json_from_kafka. For example:

gpmaster$ psql -d testdb

testdb=# CREATE TABLE json_from_kafka( customer_id int8, month int4, amount_paid decimal(9,2) );

Exit the psql subsystem:
```
testdb=# \q
```
Submit the Kafka data load job to the GPSS instance running on port number 50007. (You may consider opening a new terminal window to run the command.) For example to submit a job named kafkajson2gp:
```
gpmaster$ gpsscli submit --name kafkajson2gp --gpss-port 50007 ./jsonload_cfg.yaml
20181214:22:37:49.168 gpsscli:gpadmin:gpmaster:075435-[INFO]:-JobID: kafkajson2gp
```

List all GPSS jobs. For example:

gpmaster$ gpsscli list --all --gpss-port 50007
JobID            GPHost        GPPort  DataBase      Schema     Table                Topic                Status  
kafkajson2gp     localhost     5432    testdb        public     json_from_kafka      topic_json_gpkafka   Stopped

The list subcommand displays all jobs. Notice the entry for the kafkajson2gp that you just submitted, and that the job is in the Stopped state.

Start the job named kafkajson2gp. For example:

gpmaster$ gpsscli start kafkajson2gp --gpss-port 50007
20181214:22:43:32.590 gpsscli:gpadmin:gpmaster:075490-[INFO]:-JobID: kafkajson2gp is started

Stop the job named kafkajson2gp. For example:

gpmaster$ gpsscli stop kafkajson2gp --gpss-port 50007
20181214:22:51:21.960 gpsscli:gpadmin:e11517afb6f6:075781-[INFO]:-Stop a job: kafkajson2gp, status Stopped

Examine the gpss command output and log file, looking for messages that identify the number of rows inserted/rejected. For example:
```
... -[INFO]:- ... Inserted 9 rows
... -[INFO]:- ... Rejected 0 rows
```

View the contents of the Greenplum Database target table json_from_kafka:

gpmaster$ psql -d testdb

testdb=# SELECT * FROM json_from_kafka WHERE customer_id='1313131' 
           ORDER BY amount_paid;
 customer_id | month | amount_paid 
-------------+-------+-------------
     1313131 |    11 |      368.27
     1313131 |    10 |      492.83
     1313131 |    12 |     1313.13
(3 rows)