[jira] [Created] (CASSANDRA-8449) Allow zero-copy reads again

["T Jake Luciani (JIRA)" <ji...@apache.org>]

T Jake Luciani created CASSANDRA-8449:
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             Summary: 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
            Priority: Minor
             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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