Why is the consistency level changing from LOCAL_QUORUM to TWO?

Question

question

vkayanala_42513 asked · May 13 at 01:44 PM

Why is the consistency level changing from LOCAL_QUORUM to TWO?

Hi Support,

Our applications are configured to LOCAL_QUORUM on both reads and writes. Lately, we are noticing

com.datastax.driver.core.exceptions.WriteFailureException: Cassandra failure during write query at consistency TWO (2 responses were required but only 1 replica responded, 1 failed).

Not sure where this CL TWO coming from!

Along with this, noticing this below warn in system.log when CL TWO happened.

WARN [MessagingService-Incoming-/x.x.x.x] 2020-05-13 05:47:55,216 MessagingService.java:848 - Backpressure rejection while receiving WRITES.BATCH_STORE from /x.x.x.x

Thank You.

cassandra

10 |1000 characters needed characters left characters exceeded

Attachments: Up to 8 attachments (including images) can be used with a maximum of 1.0 MiB each and 10.0 MiB total.

Answer 1 · 2020-05-14T04:31:39Z

yukim answered · May 14 at 04:31 AM

Are you writing data with batch (BEGIN BATCH ... APPLY BATCH)?

When doing batch, Cassandra first writes batch log to several nodes in the cluster in case of failure. When you are writing data with CL of more than ONE, then batch log writing will use CL of TWO to replicate the batch log.

The error indicates it couldn't replicate batch log.

BTW if you are using Materialized View, updating MV uses batch as well, so that can be the case as well.

3 Share

10 |1000 characters needed characters left characters exceeded

Attachments: Up to 8 attachments (including images) can be used with a maximum of 1.0 MiB each and 10.0 MiB total.

Erick Ramirez ♦♦ · May 14 at 04:57 AM

Thanks for the clarification. I forgot to consider the failed batch log writes which makes sense from WriteFailureException which is returned by the coordinator when the replica write fails for batch writes.

0 · ·

vkayanala_42513 · May 14 at 01:56 PM

@yukim We are doing single partition batches. I have read that "No batchlog mechanism is necessary for single partition batching". Source: https://docs.datastax.com/en/cql-oss/3.3/cql/cql_using/useBatch.html

Our batch query is like this: BATCH of 1 (with 1 others) : INSERT INTO from_link (from_id,link_type,to_id) VALUES (?,?,?);

and not using MV's.

0 · ·

Erick Ramirez ♦♦ vkayanala_42513 · May 15 at 01:16 AM

What does this mean?

BATCH of 1 (with 1 others)

0 · ·

question