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From "Robert Stupp (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-11870) Consider allocating direct buffers bypassing ByteBuffer.allocateDirect
Date Sun, 22 May 2016 16:15:12 GMT
Robert Stupp created CASSANDRA-11870:
----------------------------------------

             Summary: Consider allocating direct buffers bypassing ByteBuffer.allocateDirect
                 Key: CASSANDRA-11870
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-11870
             Project: Cassandra
          Issue Type: Improvement
            Reporter: Robert Stupp
            Priority: Minor


As outlined in CASSANDRA-11818, {{ByteBuffer.allocateDirect}} uses {{Bits.reserveMemory}},
which is there to respect the JVM setting {{-XX:MaxDirectMemorySize=...}}.

{{Bits.reserveMemory}} first tries an "optimistic" {{tryReserveMemory}} and exits immediately
on success. However, if that somehow doesn't succeed, it triggers a {{System.gc()}}, which
is bad IMO (however, kind of how direct buffers work in Java). After that GC it sleeps and
tries to reserve the memory up to 9 times - up to 511 ms - and then throws {{OutOfMemoryError("Direct
buffer memory")}}.

This is unnecessary for us since we always immediately "free" direct buffers as soon as we
no longer need them.

Proposal: Manage direct-memory reservations in our own code and skip {{Bits.reserveMemory}}
that way.

(However, Netty direct buffers are not under our control.)



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