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From Gianluca Borello <>
Subject Re: Pending compactions not going down on some nodes of the cluster
Date Mon, 21 Mar 2016 21:29:48 GMT
On Mon, Mar 21, 2016 at 2:15 PM, Alain RODRIGUEZ <> wrote:

> What hardware do you use? Can you see it running at the limits (CPU /
> disks IO)? Is there any error on system logs, are disks doing fine?
Nodes are c3.2xlarge instances on AWS. The nodes are relatively idle, and,
as said in the original email, the other nodes are handling the same load
and are doing just fine (no warnings or errors in the system and cassandra
logs). I mean, even this node is doing very fine, it seems as if there is
some internal bug in the way pending tasks are counted.

> How is configured the concurrent_compactors setting? It looks like you are
> using 2 from 'nodetool compactionstats' output. Could you increase that
> or is it the number of cores of the machine?
It's 2. I can certainly increase it, but, as I proved earlier, it doesn't
do anything, because if I do a "nodetool drain" and wait a while, the
compactions completely stop (and the node goes totally idle), despite the
pending compactions remaining high, so this really doesn't feel like a
problem of Cassandra not being able to keep up with the compactions.

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