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https://issues.apache.org/jira/browse/CASSANDRA-8885?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Carl Yeksigian resolved CASSANDRA-8885.
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Resolution: Duplicate
Fix Version/s: 2.0.4
As part of [~thobbs]'s fix for CASSANDRA-6483, he addressed an issue where even
if cold_reads_to_omit was 0.0, it would still filter out sstables which hadn't
been read from. Upgrading to 2.0.4+ should address this issue.
> Cold sstable count increases indefinitely in STCS
> -------------------------------------------------
>
> Key: CASSANDRA-8885
> URL: https://issues.apache.org/jira/browse/CASSANDRA-8885
> Project: Cassandra
> Issue Type: Bug
> Components: Core
> Environment: Cassandra 2.0.3
> Reporter: Anuj
> Priority: Minor
> Fix For: 2.0.4
>
>
> This issue is regarding compaction of cold sstables.
> Compaction Strategy for CF: Size Tiered (Min Threshold=4 & Max Threshold=8)
> Scenario: Run heavy write load (with NO reads) on all 3 nodes of Cassandra
> cluster. After some time, compactions stop and sstable count increases
> continuously to large numbers (90+) . As writes continue, small sstable of
> similar size are added after every few minutes. When writes stop and
> Cassandra is idle, compaction doesn't happen automatically and sstable count
> is still very high. When we start reads on sstables, compaction is
> automatically triggered and sstable count keeps on decreasing to reasonable
> levels.
> We think that behaviour is unexpected because of following reasons:
> 1. As per documentation
> (https://issues.apache.org/jira/browse/CASSANDRA-6109 and
> http://www.datastax.com/dev/blog/optimizations-around-cold-sstables),
> cold_reads_to_omit is disabled by default in 2.0.3. We are using 2.0.3 and
> not enabled cold_reads_to_omit explicitly. Still, cold sstables are not
> getting compacted. Coldness should not come in picture by default in 2.0.3.
> Note:compactionstats show 0 pending tasks while compaction process is
> not happening.
>
> 2. In our scenario, we have heavy writes (say for loading data)
> followed by reads. Till the time read starts, you have huge no. of sstables
> to compact.Significant compactions need to be done before read performance is
> restored.
>
> 3. Even when Cassandra is kept idle after writes, compaction doesn't
> happen. Dont you think compaction should not just look at coldness? It should
> also consider load on server and utilize time for compaction when possible.
> Cold sstables can be compacted together. This way we will have much less
> compactions to do if cold sstables turn hot.
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