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From "Benedict (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-8833) Stop opening compaction results early
Date Mon, 09 Mar 2015 14:03:39 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-8833?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14353003#comment-14353003
] 

Benedict commented on CASSANDRA-8833:
-------------------------------------

bq.  I think it would be OK to run it straight up current 2.1 vs current 2.1 with sstable_preemptive_open_interval_in_mb:
-1 as well, just to get a feeling for it

This isn't a like-for-like comparison, as without preemptive open we need to evict the page
cache for compaction results to avoid inactive data polluting it.

> Stop opening compaction results early
> -------------------------------------
>
>                 Key: CASSANDRA-8833
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-8833
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Marcus Eriksson
>             Fix For: 2.1.4
>
>
> We should simplify the code base by not doing early opening of compaction results. It
makes it very hard to reason about sstable life cycles since they can be in many different
states, "opened early", "starts moved", "shadowed", "final", instead of as before, basically
just one (tmp files are not really 'live' yet so I don't count those). The ref counting of
shared resources between sstables in these different states is also hard to reason about.
This has caused quite a few issues since we released 2.1
> I think it all boils down to a performance vs code complexity issue, is opening compaction
results early really 'worth it' wrt the performance gain? The results in CASSANDRA-6916 sure
look like the benefits are big enough, but the difference should not be as big for people
on SSDs (which most people who care about latencies are)
> WDYT [~benedict] [~jbellis] [~iamaleksey] [~JoshuaMcKenzie]?



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