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From Vitaliy Semochkin <vitaliy...@gmail.com>
Subject Re: commitlog content
Date Thu, 30 Aug 2018 16:57:10 GMT
Thank you for the  excellent response Alain!
On Thu, Aug 30, 2018 at 5:25 PM Alain RODRIGUEZ <arodrime@gmail.com> wrote:
>
> Hello Vitaly.
>
> This sounds weird to me (unless we are speaking about a small size MB, a few GB maybe).
Then the commit log size is limited, by default (see below) and the data should grow bigger
in most cases.
>
> According to the documentation (http://cassandra.apache.org/doc/latest/architecture/storage_engine.html#commitlog):
>
>> commitlog_total_space_in_mb: Total space to use for commit logs on disk.
>> If space gets above this value, Cassandra will flush every dirty CF in the oldest
segment and remove it. So a small total commitlog space will tend to cause more flush activity
on less-active columnfamilies.
>> The default value is the smaller of 8192, and 1/4 of the total space of the commitlog
volume.
>> Default Value: 8192
>
>
> The commit log is supposed to be cleaned on flush, thus the solution to reduce the disk
space used by commit logs are multiple:
> - Decrease the value for 'commitlog_total_space_in_mb' (probably the best option, you
say what you want, and you get it)
> - Use the table option 'memtable_flush_period_in_ms' (default is 0, pick what you would
like here - has to be done on all the table you want it to apply)
> - Manually run: 'nodetool flush' should also clean the commit logs
> - Reduce the size of the memtables
> - Limit the maximum size per table before a flush is triggered with 'memtable_cleanup_threshold'.
According to the doc it's not a good idea though (http://cassandra.apache.org/doc/latest/configuration/cassandra_config_file.html#memtable-cleanup-threshold).
>
> Also, the data in Cassandra is compacted and compressed. Over a short time period of
test or if the data is small compared to the memory available and fits mostly in memory, I
can imagine that what you describe can happen.
>
> C*heers,
> -----------------------
> Alain Rodriguez - @arodream - alain@thelastpickle.com
> France / Spain
>
> The Last Pickle - Apache Cassandra Consulting
> http://www.thelastpickle.com
>
> Le mar. 28 août 2018 à 18:24, Vitaliy Semochkin <vitaliy.se@gmail.com> a écrit
:
>>
>> Hello,
>>
>> I've noticed that after a stress test that does only inserts a
>> commitlog content exceeds data dir 20 times.
>> What can be cause of such behavior?
>>
>> Running nodetool compact did not change anything.
>>
>> Regards,
>> Vitaliy
>>
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