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From "Marcus Eriksson (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-8371) DateTieredCompactionStrategy is always compacting
Date Tue, 25 Nov 2014 07:18:12 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-8371?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14224143#comment-14224143
] 

Marcus Eriksson commented on CASSANDRA-8371:
--------------------------------------------

Did you start fresh with DTCS? If not, then it makes sense, you will have totally mixed timestamps
in your sstables, meaning you will most likely spend alot of time compacting

> DateTieredCompactionStrategy is always compacting 
> --------------------------------------------------
>
>                 Key: CASSANDRA-8371
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-8371
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>            Reporter: mck
>              Labels: compaction, performance
>         Attachments: java_gc_counts_rate-month.png, read-latency.png, sstables.png, vg2_iad-month.png
>
>
> Running 2.0.11 and having switched a table to [DTCS|https://issues.apache.org/jira/browse/CASSANDRA-6602]
we've seen that disk IO and gc count increase, along with the number of reads happening in
the "compaction" hump of cfhistograms.
> Data, and generally performance, looks good, but compactions are always happening, and
pending compactions are building up.
> The schema for this is 
> {code}CREATE TABLE search (
>   loginid text,
>   searchid timeuuid,
>   description text,
>   searchkey text,
>   searchurl text,
>   PRIMARY KEY ((loginid), searchid)
> );{code}
> We're sitting on about 82G (per replica) across 6 nodes in 4 DCs.
> CQL executed against this keyspace, and traffic patterns, can be seen in slides 7+8 of
https://prezi.com/b9-aj6p2esft
> Attached are sstables-per-read and read-latency graphs from cfhistograms, and screenshots
of our munin graphs as we have gone from STCS, to LCS (week ~44), to DTCS (week ~46).
> These screenshots are also found in the prezi on slides 9-11.
> [~pmcfadin], [~Bj0rn], 
> Can this be a consequence of occasional deleted rows, as is described under (3) in the
description of CASSANDRA-6602 ?



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