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From "Benedict (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-7039) DirectByteBuffer compatible LZ4 methods
Date Tue, 15 Apr 2014 12:39:15 GMT
Benedict created CASSANDRA-7039:
-----------------------------------

             Summary: DirectByteBuffer compatible LZ4 methods
                 Key: CASSANDRA-7039
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-7039
             Project: Cassandra
          Issue Type: Improvement
          Components: Core
            Reporter: Benedict
            Priority: Minor


As we move more things off-heap, it's becoming more and more essential to be able to use DirectByteBuffer
(or native pointers) in various places. Unfortunately LZ4 doesn't currently support this operation,
despite being JNI based - this means we both have to perform unnecessary copies to de/compress
data from DBB, but also we can stall GC as any JNI method operating over a java array using
the GetPrimitiveArrayCritical enters a critical section that prevents GC for its duration.
This means STWs will be at least as long any running compression/decompression (and no GC
will happen until they complete, so it's additive).

We should temporarily fork (and then resubmit upstream) jpountz-lz4 to support operating over
a native pointer, so that we can pass a DBB or a raw pointer we have allocated ourselves.
This will help improve performance when flushing the new offheap memtables, as well as enable
us to implement CASSANDRA-6726 and finish CASSANDRA-4338.



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