Heiko Sommer created CASSANDRA-12699:
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Summary: Excessive use of "hidden" Linux page table memory
Key: CASSANDRA-12699
URL: https://issues.apache.org/jira/browse/CASSANDRA-12699
Project: Cassandra
Issue Type: Bug
Components: Core
Environment: Cassandra 2.2.7 on Red Hat 6.7, with Java 1.8.0_73.
Probably others.
Reporter: Heiko Sommer
Attachments: PageTableMemoryExample.png, cassandra-env.sh,
cassandra.yaml, cassandraMemoryLog.sh
The cassandra JVM process uses many gigabytes of page table memory during
certain activities, which can lead to oom-killer action with
"java.lang.OutOfMemoryError: null" logs.
Page table memory is not reported by Linux tools such as "top" or "ps" and
therefore might be responsible also for other spurious Cassandra issues with
"memory eating" or crashes, e.g. CASSANDRA-8723.
The problem happens especially (or only?) during large compactions and
anticompactions.
Eventually all memory gets released, which means there is no real leak. Still I
suspect that the memory mappings that fill the page table could be released
much sooner, to keep the page table size at a small fraction of the total
Cassandra process memory.
How to reproduce: Record the memory use on a Cassandra node, including page
table memory, for example using the attached script cassandraMemoryLog.sh. Even
when there is no crash, the ramping up and sudden release of page table memory
is visible.
A stacked area plot for the memory on one of our crashed nodes is attached
(PageCacheMemoryExample.png). The page table memory used by Cassandra is shown
in red ("VmPTE").
(In the plot we also see that the sum of measured memory portions sometimes
exceeds the total memory. This is probably an issue of how RSS memory is
measured, perhaps including some buffers/cache memory that also counts toward
available memory. It does not invalidate the finding that page table memory is
growing to enormous sizes.)
Shortly before the crash, /proc/$PID/status reported
VmPeak: 6989760944 kB
VmSize: 5742400572 kB
VmLck: 4735036 kB
VmHWM: 8589972 kB
VmRSS: 7022036 kB
VmData: 10019732 kB
VmStk: 92 kB
VmExe: 4 kB
VmLib: 17584 kB
VmPTE: 3965856 kB
VmSwap: 0 kB
The config files cassandra.yaml and cassandra-env.sh used on the node where the
data was taken are attached.
Please let me know if I should provide any other data or descriptions to help
with this ticket.
Known workaround: Use more RAM, or limit the amount of Java heap memory. In the
above crash, MAX_HEAP_SIZE was not set, so that the default heap size for 12 GB
RAM was used.
We have not tried yet if variations of heap vs. offheap config choices make a
difference.
Perhaps there are other workarounds using -XX+UseLargePages or related Linux
settings to reduce the size of the process page table?
I believe that we see these crashes more often than other projects because we
have a test system with not much RAM but with a lot of data (~3 TB per node
compressed), while the CPUs are slow so that anti-/compactions overlap a lot.
Ideally Cassandra (native) code should be changed to release memory in smaller
chunks, so that page table size cannot cause an otherwise stable system to
crash.
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