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From Oleksandr Shulgin <oleksandr.shul...@zalando.de>
Subject Re: failing bootstraps with OOM
Date Wed, 02 Nov 2016 17:07:44 GMT
On Wed, Nov 2, 2016 at 3:35 PM, Mike Torra <mtorra@demandware.com> wrote:
>
> Hi All -
>
> I am trying to bootstrap a replacement node in a cluster, but it
consistently fails to bootstrap because of OOM exceptions. For almost a
week I've been going through cycles of bootstrapping, finding errors, then
restarting / resuming bootstrap, and I am struggling to move forward.
Sometimes the bootstrapping node itself fails, which usually manifests
first as very high GC times (sometimes 30s+!), then nodetool commands start
to fail with timeouts, then the node will crash with an OOM exception.
Other times, a node streaming data to this bootstrapping node will have a
similar failure. In either case, when it happens I need to restart the
crashed node, then resume the bootstrap.
>
> On top of these issues, when I do need to restart a node it takes a
loooong time (
http://stackoverflow.com/questions/40141739/why-does-cassandra-sometimes-take-a-hours-to-start).
This exasperates the problem because it takes so long to find out if a
change to the cluster helps or if it still fails. I am in the process of
upgrading all nodes in the cluster from m4.xlarge to c4.4xlarge, and I am
running Cassandra DDC 3.5 on all nodes. The cluster has 26 nodes spread
across 4 regions in EC2. Here is some other relevant cluster info (also in
stack overflow post):
>
> Cluster Info
>
> Cassandra DDC 3.5
> EC2MultiRegionSnitch
> m4.xlarge, moving to c4.4xlarge
>
> Schema Info
>
> 3 CF's, all 'write once' (ie no updates), 1 week ttl, STCS (default)
> no secondary indexes
>
> I am unsure what to try next. The node that is currently having this
bootstrap problem is a pretty beefy box, with 16 cores, 30G of ram, and a
3.2T EBS volume. The slow startup time might be because of the issues with
a high number of SSTables that Jeff Jirsa mentioned in a comment on the SO
post, but I am at a loss for the OOM issues. I've tried:
>
> Changing from CMS to G1 GC, which seemed to have helped a bit
> Upgrading from 3.5 to 3.9, which did not seem to help
> Upgrading instance types from m4.xlarge to c4.4xlarge, which seems to
help, but I'm still having issues
>
> I'd appreciate any suggestions on what else I can try to track down the
cause of these OOM exceptions.

Hi,

Do you monitor pending compactions and actual number of SSTable files?

On startup Cassandra needs to touch most of the data files and also seems
to keep some metadata about every relevant file in memory.  We once went
into situation where we ended up with hundreds of thousands of files per
node which resulted in OOMs on every other node of the ring, and startup
time was of over half an hour (this was on version 2.1).

If you have much more files than you expect, then you should check and
adjust your concurrent_compactors and compaction_throughput_mb_per_sec
settings.  Increase concurrent_compactors if you're behind (pending
compactions metric is a hint) and consider un-throttling compaction before
your situation is back to normal.

Cheers,
--
Alex

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