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https://issues.apache.org/jira/browse/CASSANDRA-6916?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13976788#comment-13976788
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Marcus Eriksson commented on CASSANDRA-6916:
--------------------------------------------
new patch comments;
* cleanup is broken, first the log message causes npe since newSstable is null,
secondly, an immutableSet is passed as rewriting to SSTableRewriter, causing
moveStarts to fail since it calls removeAll on that set. Both fixed here:
https://github.com/krummas/cassandra/commits/bes/6916-2
* a bit of javadoc around moveStarts could be helpful, just looking at the api
now makes it feel like we are moving the start of newReader
* when doing anticompaction, should we not clean up old readers?
(repairedSSTableWriter.finish(false, repairedAt);)
* do we need to move starts back in SSTableRewriter.resetAndTruncate()? If we
resetAndTruncate right after doing early opening, i think we could create a gap
between the start in the compacting file and the end in the written one
> Preemptive opening of compaction result
> ---------------------------------------
>
> Key: CASSANDRA-6916
> URL: https://issues.apache.org/jira/browse/CASSANDRA-6916
> Project: Cassandra
> Issue Type: Bug
> Components: Core
> Reporter: Benedict
> Assignee: Benedict
> Priority: Minor
> Labels: performance
> Fix For: 2.1
>
> Attachments: 6916-stock2_1.mixed.cache_tweaks.tar.gz,
> 6916-stock2_1.mixed.logs.tar.gz, 6916v3-preempive-open-compact.logs.gz,
> 6916v3-preempive-open-compact.mixed.2.logs.tar.gz,
> 6916v3-premptive-open-compact.mixed.cache_tweaks.2.tar.gz
>
>
> Related to CASSANDRA-6812, but a little simpler: when compacting, we mess
> quite badly with the page cache. One thing we can do to mitigate this problem
> is to use the sstable we're writing before we've finished writing it, and to
> drop the regions from the old sstables from the page cache as soon as the new
> sstables have them (even if they're only written to the page cache). This
> should minimise any page cache churn, as the old sstables must be larger than
> the new sstable, and since both will be in memory, dropping the old sstables
> is at least as good as dropping the new.
> The approach is quite straight-forward. Every X MB written:
> # grab flushed length of index file;
> # grab second to last index summary record, after excluding those that point
> to positions after the flushed length;
> # open index file, and check that our last record doesn't occur outside of
> the flushed length of the data file (pretty unlikely)
> # Open the sstable with the calculated upper bound
> Some complications:
> # must keep running copy of compression metadata for reopening with
> # we need to be able to replace an sstable with itself but a different lower
> bound
> # we need to drop the old page cache only when readers have finished
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