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From Sergey Murylev <sergeymury...@gmail.com>
Subject Re: Timeseries with TTL
Date Sun, 06 Apr 2014 13:33:53 GMT
Hi Vincent,

> Is that a good pattern for Cassandra? Is there some compaction tunings
> I should take into account?
Actually it depends on how you use Cassandra :). If you use it as
key-value storage TTL works fine. But if you would use rather complex
CQL queries to this table I not sure that it would be good.

> With this structure is obvious that after one week inserting data,
> from that moment there's gonna be new expired columns every 5 minutes
> in that table. Because of that I've noticed that this table is being
> compacted every 5 minutes.
Compaction doesn't triggered when some column expired. It triggered on
gc_grace_seconds timeout and according compaction strategy. You can see
more detailed description of LeveledCompactionStrategy in following
article: Leveled compaction in Cassandra
<http://www.datastax.com/dev/blog/leveled-compaction-in-apache-cassandra>.

There are 2 types of compaction: minor and major, which kind of
compaction do you see and how come to conclusion that compaction
triggered every 5 minutes? If you see major compaction that situation is
very bad otherwise it is normal case.

--
Thanks,
Sergey


On 06/04/14 15:48, Vicent Llongo wrote:
> Hi there,
>
> I have this table where I'm inserting timeseries values with a TTL of
> 86400*7 (1week):
>
> CREATE TABLE metrics_5min (
>   object_id varchar,
>   metric varchar,
>   ts timestamp,
>   val double,
>   PRIMARY KEY ((object_id, metric), ts)
> )
> WITH gc_grace_seconds = 86400
> AND compaction = {'class': 'LeveledCompactionStrategy',
> 'sstable_size_in_mb' : 100};
>
>
> With this structure is obvious that after one week inserting data,
> from that moment there's gonna be new expired columns every 5 minutes
> in that table. Because of that I've noticed that this table is being
> compacted every 5 minutes.
>
> Is that a good pattern for Cassandra? Is there some compaction tunings
> I should take into account?
>
> Thanks!
>
>


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