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From Hannes Schmidt <han...@eyealike.com>
Subject Native heap leaks?
Date Wed, 04 May 2011 18:50:22 GMT
Hi,

We are using Cassandra 0.6.12 in a cluster of 9 nodes. Each node is
64-bit, has 4 cores and 4G of RAM and runs on Ubuntu Lucid with the
stock 2.6.32-31-generic kernel. We use the Sun/Oracle JDK.

Here's the problem: The Cassandra process starts up with 1.1G resident
memory (according to top) but slowly grows to 2.1G at a rate that
seems proportional to the write load. No writes, no growth. The node
is running other memory-sensitive applications (a second JVM for our
in-house webapp and a short-lived C++ program) so we need to ensure
that each process stays within certain bounds as far as memory
requirements go. The nodes OOM and crash when the Cassandra process is
at 2.1G so I can't say if the growth is bounded or not.

Looking at theĀ /proc/$pid/smapsĀ for the Cassandra process it seems to
me that it is the native heap of the Cassandra JVM that is leaking. I
attached a readable version of the smaps file generated by [1].

Some more data: Cassandra runs with default command line arguments,
which means it gets 1G heap. The JNA jar is present and Cassandra logs
that the memory locking was successful. In storage-conf.xml,
DiskAccessMode is mmap_index_only. Other than that and some increased
timeouts we left the defaults. Swap is completely disabled. I don't
think this is related but I am mentioning it anyways: overcommit [2]
is always-on (vm.overcommit_memory=1). Without that we get OOMs when
our application JVM is fork()'ing and exec()'ing our C++program even
though there is enough free RAM to satisfy the demands of the C++
program. We think this is caused by a flawed kernel heuristic that
assumes that the forked process (our C++ app) is as big as the forking
one (the 2nd JVM). Anyways, the Cassandra process leaks with both,
vm.overcommit_memory=0 (the default) and 1.

Whether it is the native heap that leaks or something else, I think
that 1.1G of additional RAM for 1G of Java heap can't be normal. I'd
be grateful for any insights or pointers at what to try next.

[1] http://bmaurer.blogspot.com/2006/03/memory-usage-with-smaps.html
[2] http://www.win.tue.nl/~aeb/linux/lk/lk-9.html#ss9.6

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