Cassandra

Kafka Connect Cassandra is a Source Connector for reading data from Cassandra and writing to Kafka.

KCQL support 

The following KCQL is supported:

INSERT INTO <your-topic>
SELECT FIELD,...
FROM <your-cassandra-table>
[PK FIELD]
[WITHFORMAT JSON]
[INCREMENTALMODE=TIMESTAMP|TIMEUUID|TOKEN|DSESEARCHTIMESTAMP]
[WITHKEY(<your-key-field>)]

Examples:

-- Select all columns from table orders and insert into a topic
-- called orders-topic, use column created to track new rows.
-- Incremental mode set to TIMEUUID
INSERT INTO orders-topic SELECT * FROM orders PK created INCREMENTALMODE=TIMEUUID

-- Select created, product, price from table orders and insert
-- into a topic called orders-topic, use column created to track new rows.
INSERT INTO orders-topic SELECT created, product, price FROM orders PK created.

Concepts 

The connector can load data in two ways:

1. Bulk - The connector constantly loads the entrie table.
2. Incremental - The connector performs and inital bulk load then incremental queries for new records.

This behavior is determined by the mode clause on the KCQL statement:

Keyed JSON Format 

The connector can write JSON to your Kafka topic using the WITHFORMAT JSON clause but the key and value converters must be set:

key.converter=org.apache.kafka.connect.storage.StringConverter
value.converter=org.apache.kafka.connect.storage.StringConverter

In order to facilitate scenarios like retaining the latest value for a given device identifier, or support Kafka Streams joins without having to re-map the topic data the connector supports WITHKEY in the KCQL syntax.

INSERT INTO <topic>
SELECT <fields>
FROM <column_family>
PK <PK_field>
WITHFORMAT JSON
WITHUNWRAP INCREMENTALMODE=<mode>
WITHKEY(<key_field>)

Multiple keys fields are supported using a delimiter:

// `[` enclosed by `]` denotes optional values
WITHKEY(field1 [, field2.A , field3]) [KEYDELIMITER='.']

The resulting Kafka record key content will be the string concatenation for the values of the fields specified. Optionally the delimiter can be set via the KEYDELIMITER keyword.

Incremental mode 

This mode tracks new records added to a table. The columns to track is identified by the PK clause in the KCQL statement. Only one column can be used to track new records. The support Cassandra column data types are:

1. TIMESTAMP
2. TIMEUUID
3. TOKEN
4. DSESEARCHTIMESTAMP

If set to TOKEN this column value is wrapped inside Cassandras token function which needs unwrapping with the WITHUNWRAP command.

DSESEARCHTIMESTAMP will make a DSE Search queries using Solr instead of a native Cassandra query.

INSERT INTO <topic>
SELECT a, b, c, d
FROM keyspace.table
WHERE solr_query= 'pkCol:{2020-03-23T15:02:21Z TO 2020-03-23T15:30:12.989Z]}'
INCREMENTALMODE=DSESEARCHTIMESTAMP

Controlling throughput 

The connector can be configured to:

• Start from a particular offset - connect.cassandra.initial.offset
• Increase or decrease the poll interval - connect.cassandra.import.poll.interval
• Set a slice duration to query for in milliseconds - ``connect.cassandra.slice.duration`

For a more detailed explanation on how to use Cassandra to Kafka options.

Quickstart 

Launch the stack 

1. Copy the docker-compose file.
2. Bring up the stack.

export CONNECTOR=cassandra
docker-compose up -d cassandra

Inserting test data 

Login into your container:

docker exec -ti cassandra cqlsh

and and create the following keyspace, table and insert test data:

CREATE KEYSPACE demo
WITH REPLICATION = {'class' : 'SimpleStrategy', 'replication_factor' : 3};

USE demo;

CREATE TABLE orders (
    id int
    , created timeuuid
    , product text
    , qty int
    , price float
    , PRIMARY KEY (id, created))
WITH CLUSTERING ORDER BY (created asc);

INSERT INTO orders (id, created, product, qty, price)
VALUES (1, now(), 'OP-DAX-P-20150201-95.7', 100, 94.2);

INSERT INTO orders (id, created, product, qty, price)
VALUES (2, now(), 'OP-DAX-C-20150201-100', 100, 99.5);

INSERT INTO orders (id, created, product, qty, price)
VALUES (3, now(), 'FU-KOSPI-C-20150201-100', 200, 150);

Start the connector 

If you are using Lenses, login into Lenses and navigate to the connectors page, select Cassandra as the source and paste the following:

name=cassandra
connector.class=io.lenses.streamreactor.connect.cassandra.source.CassandraSourceConnector
connect.cassandra.key.space=demo
connect.cassandra.kcql=INSERT INTO orders-topic SELECT * FROM orders PK created INCREMENTALMODE=TIMEUUID
connect.cassandra.contact.points=cassandra

To start the connector using the command line, log into the lenses-box container:

docker exec -ti lenses-box /bin/bash

and create a connector.properties file containing the properties above.

Create the connector, with the connect-cli:

connect-cli create cassandra-source < connector.properties

Wait for the connector to start and check it’s running:

connect-cli status cassandra-source

Check for records in Kafka 

Check the records in Lenses or with via the console:

kafka-avro-console-consumer \
    --bootstrap-server localhost:9092 \
    --topic orders-topic \
    --from-beginning

Source Data Type Mapping 

The following CQL data types are supported:

Options