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https://issues.apache.org/jira/browse/CASSANDRA-8449?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14361107#comment-14361107
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T Jake Luciani commented on CASSANDRA-8449:
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I've updated my branch with the oporder approach for netty and message service
requests. There are still edges like dropped messages and internal cql
requests I need to cover. As well as hints and batchlog replay (though those
are compressed so shouldn't be an issue regardless).
I've added a unit test using ByteMan http://byteman.jboss.org/ to inject pauses
in the pipeline that cause the jvm to crash without the correct oporder code.
> Allow zero-copy reads again
> ---------------------------
>
> Key: CASSANDRA-8449
> URL: https://issues.apache.org/jira/browse/CASSANDRA-8449
> Project: Cassandra
> Issue Type: Improvement
> Reporter: T Jake Luciani
> Assignee: T Jake Luciani
> Priority: Minor
> Labels: performance
> Fix For: 3.0
>
>
> We disabled zero-copy reads in CASSANDRA-3179 due to in flight reads
> accessing a ByteBuffer when the data was unmapped by compaction. Currently
> this code path is only used for uncompressed reads.
> The actual bytes are in fact copied to the client output buffers for both
> netty and thrift before being sent over the wire, so the only issue really is
> the time it takes to process the read internally.
> This patch adds a slow network read test and changes the tidy() method to
> actually delete a sstable once the readTimeout has elapsed giving plenty of
> time to serialize the read.
> Removing this copy causes significantly less GC on the read path and improves
> the tail latencies:
> http://cstar.datastax.com/graph?stats=c0c8ce16-7fea-11e4-959d-42010af0688f&metric=gc_count&operation=2_read&smoothing=1&show_aggregates=true&xmin=0&xmax=109.34&ymin=0&ymax=5.5
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