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From Evelyn Smith <>
Subject Re: OOM after a while during compacting
Date Thu, 05 Apr 2018 13:14:45 GMT
Probably a dumb question but it’s good to clarify.

Are you compacting the whole keyspace or are you compacting tables one at a time?

> On 5 Apr 2018, at 9:47 pm, Zsolt Pálmai <> wrote:
> Hi!
> I have a setup with 4 AWS nodes (m4xlarge - 4 cpu, 16gb ram, 1TB ssd each) and when running
the nodetool compact command on any of the servers I get out of memory exception after a while.
> - Before calling the compact first I did a repair and before that there was a bigger
update on a lot of entries so I guess a lot of sstables were created. The reapir created around
~250 pending compaction tasks, 2 of the nodes I managed to finish with upgrading to a 2xlarge
machine and twice the heap (but running the compact on them manually also killed one :/ so
this isn't an ideal solution)
> Some more info: 
> - Version is the newest 3.11.2 with java8u116
> - Using LeveledCompactionStrategy (we have mostly reads)
> - Heap size is set to 8GB
> - Using G1GC
> - I tried moving the memtable out of the heap. It helped but I still got an OOM last
> - Concurrent compactors is set to 1 but it still happens and also tried setting throughput
between 16 and 128, no changes.
> - Storage load is 127Gb/140Gb/151Gb/155Gb
> - 1 keyspace, 16 tables but there are a few SASI indexes on big tables.
> - The biggest partition I found was 90Mb but that table has only 2 sstables attached
and compacts in seconds. The rest is mostly 1 line partition with a few 10KB of data.
> - Worst SSTable case: SSTables in each level: [1, 20/10, 106/100, 15, 0, 0, 0, 0, 0]
> In the metrics it looks something like this before dying: <>
> What the heap dump looks like of the top objects: <>
> The load is usually pretty low, the nodes are almost idling (avg 500 reads/sec, 30-40
writes/sec with occasional few second spikes with >100 writes) and the pending tasks is
also around 0 usually.
> Any ideas? I'm starting to run out of ideas. Maybe the secondary indexes cause problems?
I could finish some bigger compactions where there was no index attached but I'm not sure
100% if this is the cause.
> Thanks,
> Zsolt

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