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https://issues.apache.org/jira/browse/CASSANDRA-9658?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14611985#comment-14611985
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Joshua McKenzie commented on CASSANDRA-9658:
--------------------------------------------
Pushed update to
[branch|https://github.com/apache/cassandra/compare/cassandra-2.2...josh-mckenzie:9658].
Added a WindowsFailedSnapshotTracker that writes a .toDelete file in
$CASSANDRA_HOME, one line per failed snapshot directory if on Windows, and
checks that file on startup and recursively delete any folders in there. I left
the deleteRecursiveOnExit logic in there as well since a) it's pretty
lightweight and simple and b) provides another avenue for us to confirm we
delete snapshots on Windows in the rare case they fail.
The only other thing I can think of for this would be having a periodic task
that attempted to delete all the snapshot files listed in .toDelete as the node
was running, so as readers were closed and files were compacted old snapshots
would be deleted. That smells way too much like SSTableDeletingTask for my
taste; I'm pretty content with the current setup given it's a temporary
holdover.
CI running:
[testall|http://cassci.datastax.com/view/Dev/view/josh-mckenzie/job/josh-mckenzie-9658-testall/3/]
-
[dtest|http://cassci.datastax.com/view/Dev/view/josh-mckenzie/job/josh-mckenzie-9658-dtest/3/].
> Re-enable memory-mapped index file reads on Windows
> ---------------------------------------------------
>
> Key: CASSANDRA-9658
> URL: https://issues.apache.org/jira/browse/CASSANDRA-9658
> Project: Cassandra
> Issue Type: Improvement
> Reporter: Joshua McKenzie
> Assignee: Joshua McKenzie
> Labels: Windows, performance
> Fix For: 2.2.x
>
>
> It appears that the impact of buffered vs. memory-mapped index file reads has
> changed dramatically since last I tested. [Here's some results on various
> platforms we pulled together yesterday
> w/2.2-HEAD|https://docs.google.com/spreadsheets/d/1JaO2x7NsK4SSg_ZBqlfH0AwspGgIgFZ9wZ12fC4VZb0/edit#gid=0].
> TL;DR: On linux we see a 40% hit in performance from 108k ops/sec on reads to
> 64.8k ops/sec. While surprising in itself, the really unexpected result (to
> me) is on Windows - with standard access we're getting 16.8k ops/second on
> our bare-metal perf boxes vs. 184.7k ops/sec with memory-mapped index files,
> an over 10-fold increase in throughput. While testing w/standard access,
> CPU's on the stress machine and C* node are both sitting < 4%, network
> doesn't appear bottlenecked, resource monitor doesn't show anything
> interesting, and performance counters in the kernel show very little. Changes
> in thread count simply serve to increase median latency w/out impacting any
> other visible metric that we're measuring, so I'm at a loss as to why the
> disparity is so huge on the platform.
> The combination of my changes to get the 2.1 branch to behave on Windows
> along with [~benedict] and [~Stefania]'s changes in lifecycle and cleanup
> patterns on 2.2 should hopefully have us in a state where transitioning back
> to using memory-mapped I/O on Windows will only cause trouble on snapshot
> deletion. Fairly simple runs of stress w/compaction aren't popping up any
> obvious errors on file access or renaming - I'm going to do some much heavier
> testing (ccm multi-node clusters, long stress w/repair and compaction, etc)
> and see if there's any outstanding issues that need to be stamped out to call
> mmap'ed index files on Windows safe. The one thing we'll never be able to
> support is deletion of snapshots while a node is running and sstables are
> mapped, but for a > 10x throughput increase I think users would be willing to
> make that sacrifice.
> The combination of the powercfg profile change, the kernel timer resolution,
> and memory-mapped index files are giving some pretty interesting performance
> numbers on EC2.
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