Partial Cassandra Writes

Overview

This document contains observation on Batch execution with different configuration for partial writes.

Tests and Observations

For testing different scenarios keyspace and table created

CREATE KEYSPACE test WITH replication = {'class':'SimpleStrategy', 'replication_factor' : 2};

CREATE TABLE user(name text, id text, PRIMARY KEY (name));

In java

PreparedStatement preparedStatement = session.prepare("insert into test2.user (id, name) values (?, ?)");
PreparedStatement preparedStatement2 = session.prepare("update test2.user set id='id_updated-1' where name=?");
PreparedStatement preparedStatement3 = session.prepare("update test2.user set id='id_updated-2' where name=?");


int i = 1;
while(i <= 1000) {
	batchStatement.add(preparedStatement.bind("id_"+i, "user-" + i));
	++i;
}

batchStatement.add(preparedStatement2.bind("user-1"));
batchStatement.add(preparedStatement3.bind("user-2"));

In cassandra.yaml file change timeout to verify partial write

write_request_timeout_in_ms: 10

The above query will throw exception

Caused by: com.datastax.driver.core.exceptions.WriteTimeoutException: Cassandra timeout during write query at 
consistency ONE (1 replica were required but only 0 acknowledged the write)

Observation

The data got inserted into user table and got updated also as above batch execution

Suggestion

To handle above WriteTimeoutException we can use BatchStatement.Type

BatchStatement batchStatement = new BatchStatement(BatchStatement.Type.UNLOGGED);

There is 3 different types are present

BATCH_LOG
BATCH
UNLOGGED_BATCH

In cassandra doc it specifies that to increase the performance UNLOGGED_BATCH type should get use.