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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.
The default serial consistency is CASS_CONSISTENCY_ANY, which means no serial consistency specified.
This may result in an error upon execution of a statement that requires serial consistency (Lightweight Transaction, LWT).
In order to avoid this, you should set the serial consistency level to CASS_CONSISTENCY_SERIAL or CASS_CONSISTENCY_LOCAL_SERIAL
before executing such statement.
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 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.