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Consistency

A setting that defines a successful write or read by the number of cluster replicas that acknowledge the write or respond to the read request, respectively.

Default consistency

The default consistency is CASS_CONSISTENCY_LOCAL_ONE for driver versions 2.2.2 and above. In the past, versions 2.2.1 and below, it was CASS_CONSISTENCY_QUORUM or CASS_CONSISTENCY_ONE depending on the driver version.

Consistency Levels

Read and Write Consistency Levels

The consistency level determines the number of replicas on which the read/write must respond/succeed before returning an acknowledgment to the client application. Descriptions and Usage scenarios for each read/write consistency level can be found here.

Level Driver
All CASS_CONSISTENCY_ALL
Each Quorum CASS_CONSISTENCY_EACH_QUORUM
Quorum CASS_CONSISTENCY_QUORUM
Local Quorum CASS_CONSISTENCY_LOCAL_QUORUM
One CASS_CONSISTENCY_ONE
Two CASS_CONSISTENCY_TWO
Three CASS_CONSISTENCY_THREE
Local One CASS_CONSISTENCY_LOCAL_ONE
Any CASS_CONSISTENCY_ANY
Serial CASS_CONSISTENCY_SERIAL
Local Serial CASS_CONSISTENCY_LOCAL_SERIAL

NOTE: Consistency level CASS_CONSISTENCY_ANY is only valid for write operation statements.

Setting Consistency Level

A ‘CassStatement’ object can have its consistency level altered at anytime before the statement is executed by the session.

CassStatement* statement = NULL;

/* Create a simple or prepared statment */

/* Ensure the session executed statement has strong consistency */
cass_statement_set_consistency(statement, CASS_CONSISTENCY_QUORUM);

cass_statement_free(statement);

NOTE: Consistency level is ignored for USE, TRUNCATE, CREATE and ALTER statements, and some, like CASS_CONSISTENCY_ANY, aren’t allowed in all situations.