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From "Benedict (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-7039) DirectByteBuffer compatible LZ4 methods
Date Fri, 28 Nov 2014 15:24:13 GMT


Benedict commented on CASSANDRA-7039:

Is there much point upgrading without making use of the new API?

> DirectByteBuffer compatible LZ4 methods
> ---------------------------------------
>                 Key: CASSANDRA-7039
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Benedict
>            Assignee: Branimir Lambov
>            Priority: Minor
>              Labels: performance
>             Fix For: 3.0
>         Attachments: 7039.patch
> 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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