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https://issues.apache.org/jira/browse/CASSANDRA-8833?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14327970#comment-14327970
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Benedict commented on CASSANDRA-8833:
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bq. I suspect that memory mapping will eclipse performance gains
bq. I'd prefer hard #'s from test beds.
Make your mind up ;)
Joking aside, the two aren't mutually exclusive. We only rule out early
reopening with mmap because of hard links, but they only live for the duration
of the early reopening. We could delay mmapping until the final opening. The
two are also very different performance profile implications; early opening
mitigates worst case behaviour far more importantly than improving overall
system performance (although it does that too).
bq. Code-changes to stabilize this have been increasing quite a bit recently
They almost all happened within the past month, when I finished up my other
commitments and decided to try and put a lid on this and the other correlated
problems. So I'm not sure that's indicative of much.
> 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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