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https://issues.apache.org/jira/browse/CASSANDRA-6764?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13911432#comment-13911432
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Benedict commented on CASSANDRA-6764:
-------------------------------------
bq. It's good to hear this was reworked in 2.1. I hope that batching is in
there.
This particular problem won't be fixed there still. Note that the issue isn't
really with the CL, but with the process flow in the write stage. This is a
known issue, but since the workaround is so simple (increase thread count) and
relatively cost free on most platforms, it hasn't really been considered a
major problem to address.
The correct solution to this would be to perform the CL append, then place the
record on a queue to be processed once it is synced and to continue
receiving/processing other records until that time (rather than immediately
blocking on the sync).
> Using Batch commitlog_sync is slow and doesn't actually batch writes
> --------------------------------------------------------------------
>
> Key: CASSANDRA-6764
> URL: https://issues.apache.org/jira/browse/CASSANDRA-6764
> Project: Cassandra
> Issue Type: Improvement
> Components: Core
> Reporter: John Carrino
> Fix For: 1.2.16
>
> Attachments: cassandra_6764_v2.patch
>
>
> The assumption behind batch commit mode is that the client does it's own
> batching and wants to wait until the write is durable before returning. The
> problem is that the queue that cassandra uses under the covers only allows
> for a single ROW (RowMutation) per thread (concurrent_writes). This means
> that commitlog_sync_batch_window_in_ms should really be called sleep_between
> each_concurrent_writes_rows_in_ms.
> I assume the reason this slipped by for so long is that no one uses batch
> mode, probably because people say "it's slow". We need durability so this
> isn't an option.
> However it doesn't need to be this slow.
> Also, if you write a row that is larger than the commit log size it silently
> (warn) fails to put it in the commit log. This is not ideal for batch mode.
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