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From Benedict Elliott Smith <belliottsm...@datastax.com>
Subject Re: memtable mem usage off by 10?
Date Wed, 04 Jun 2014 09:56:43 GMT
If you are storing small values in your columns, the object overhead is
very substantial. So what is 400Mb on disk may well be 4Gb in memtables, so
if you are measuring the memtable size by the resulting sstable size, you
are not getting an accurate picture. This overhead has been reduced by
about 90% in the upcoming 2.1 release, through tickets 6271
<https://issues.apache.org/jira/browse/CASSANDRA-6271>, 6689
<https://issues.apache.org/jira/browse/CASSANDRA-6689> and 6694
<https://issues.apache.org/jira/browse/CASSANDRA-6694>.


On 4 June 2014 10:49, Idrén, Johan <Johan.Idren@dice.se> wrote:

>  Hi,
>
>
>  I'm seeing some strange behavior of the memtables, both in 1.2.13 and
> 2.0.7, basically it looks like it's using 10x less memory than it should
> based on the documentation and options.
>
>
>  10GB heap for both clusters.
>
> 1.2.x should use 1/3 of the heap for memtables, but it uses max ~300mb
> before flushing
>
>
>  2.0.7, same but 1/4 and ~250mb
>
>
>  In the 2.0.7 cluster I set the memtable_total_space_in_mb to 4096, which
> then allowed cassandra to use up to ~400mb for memtables...
>
>
>  I'm now running with 20480 for memtable_total_space_in_mb and cassandra
> is using ~2GB for memtables.
>
>
>  Soo, off by 10 somewhere? Has anyone else seen this? Can't find a JIRA
> for any bug connected to this.
>
> java 1.7.0_55, JNA 4.1.0 (for the 2.0 cluster)
>
>
>  BR
>
> Johan
>

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