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From "T Jake Luciani (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-8464) Support direct buffer decompression for reads
Date Wed, 17 Dec 2014 19:26:14 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-8464?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14250361#comment-14250361
] 

T Jake Luciani commented on CASSANDRA-8464:
-------------------------------------------

Why would there be an issue using mmaped data for compaction?

Throttling of compressed data is treated that way because it's in the aspect of streaming
or compaction which works on uncompressed data.

> Support direct buffer decompression for reads
> ---------------------------------------------
>
>                 Key: CASSANDRA-8464
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-8464
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: T Jake Luciani
>            Assignee: T Jake Luciani
>              Labels: performance
>             Fix For: 3.0
>
>
> Currently when we read a compressed sstable we copy the data on heap then send it to
be de-compressed to another on heap buffer (albeit pooled).
> But now both snappy and lz4 (with CASSANDRA-7039) allow decompression of direct byte
buffers.   This lets us mmap the data and decompress completely off heap (and avoids moving
bytes over JNI).
> One issue is performing the checksum offheap but the Adler32 does support in java 8 (it's
also in java 7 but marked private?!)
> This change yields a > 10% boost in read performance on cstar.  Locally I see upto
30% improvement.
> http://cstar.datastax.com/graph?stats=5ebcdd70-816b-11e4-aed6-42010af0688f&metric=op_rate&operation=2_read&smoothing=1&show_aggregates=true&xmin=0&xmax=200.09&ymin=0&ymax=135908.3



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