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From "Christian Spriegel (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-3710) Add a configuration option to disable snapshots
Date Mon, 30 Jan 2012 11:23:10 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-3710?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13196056#comment-13196056
] 

Christian Spriegel commented on CASSANDRA-3710:
-----------------------------------------------

I looked into it a bit deeper and I must admit its much more complicated than I thought. The
performance penalty is not just due to the hardlinks, but due to the memtable flushes caused
by the truncate.

What we do:
We run tests from multiple threads to improve speed. Every thread in a separate keyspace.
Between tests the current keyspace is being resetted.

What happens within cassandra:
A truncate triggered from one testthread now flushes the memtables from all other testthreads
too, which causes the testthreads to fsync each other.

How I tried to resolve this:
I removed the flush+hardlink from truncate, which made it run much faster. Unfortunetaly the
commitlog still has all the data in it and I do not see a way to drop the commitlog data withoug
flushing all CFs.

Well, I guess I will make a patch for our internal testsuite. Is anybody out there who has
the same problem, but maybe a better approach?

kind regards,
Christian
                
> Add a configuration option to disable snapshots
> -----------------------------------------------
>
>                 Key: CASSANDRA-3710
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-3710
>             Project: Cassandra
>          Issue Type: New Feature
>            Reporter: Brandon Williams
>             Fix For: 1.0.8
>
>
> Let me first say, I hate this idea.  It gives cassandra the ability to permanently delete
data at a large scale without any means of recovery.  However, I've seen this requested multiple
times, and it is in fact useful in some scenarios, such as when your application is using
an embedded cassandra instance for testing and need to truncate, which without JNA will timeout
more often than not.

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