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From "Jon Haddad (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-12805) Website documentation for commitlog
Date Wed, 26 Oct 2016 18:04:58 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-12805?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15609197#comment-15609197
] 

Jon Haddad commented on CASSANDRA-12805:
----------------------------------------

A couple notes on some improvements I think should be made. 

{quote}+In the event that Cassandra crashes, any updates that haven't been commited to the
`SSTables` would be lost.  Commitlogs 
 +provides durability for a Cassandra node by syncronizing the `Memtables` to disk.  When
starting the Cassandra node, it 
 +will load the SSTables then apply any updates in the commitlog to the memtables. {quote}

Commitlogs are an append only log of all mutations local to a Cassandra node.  Any data written
to Cassandra will first be written to a commit log before being written to a memtable.  This
provides durability in the case of unexpected shutdown.  On startup, any mutations in the
commit log will be applied.

For the different commit log sync options, It would be more informative to list them in clearly
defined sections (and use the help text from the yaml) like follows:

The commit log has the following options which control how it is synced to disk:
 
* batch: When in batch mode, Cassandra won't ack writes until the commit log has been fsynced
to disk.  It will wait commitlog_sync_batch_window_in_ms milliseconds between fsyncs. This
window should be kept short because the writer threads will be unable to do extra work while
waiting.  You may need to increase# concurrent_writes for the same reason.
* periodic: In periodic mode, writes are immediately ack'ed, and the CommitLog is simply synced
every commitlog_sync_period_in_ms milliseconds.


> Website documentation for commitlog
> -----------------------------------
>
>                 Key: CASSANDRA-12805
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-12805
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Documentation and Website
>            Reporter: Hau Phan
>            Priority: Minor
>              Labels: documentation
>         Attachments: 12805-trunk.txt
>
>
> Updated Storage Engine page for commitlogs
> Commit: https://github.com/nothau/cassandra/commit/876d395b4188bb230f869a161c3d7fe317506b34



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