Loading JSON Data from Kafka (with Mapping)

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, and use the Greenplum Streaming Server gpkafka load command to transform and 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 the loading 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.

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 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
```
Run the gpkafka load command to batch load the JSON data published to the topic_json_gpkafka topic into the Greenplum table. For example:
```
gpmaster$ gpkafka load --quit-at-eof ./jsonload_cfg.yaml
```
The command exits after it reads all data published to the topic.
Examine the command output, 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)