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From Ben Bromhead <>
Subject Re: compaction falling behind
Date Mon, 13 Feb 2017 21:49:05 GMT
You can do so in two ways:

1) direct observation:
You can keep an eye on the number of pending compactions. This will
fluctuate with load, compaction strategy, ongoing repairs and nodes
bootstrapping but generally the pattern is it should trend towards 0.

There have been a number of bugs in past versions of Cassandra whereby the
number of pending compactions is not reported correctly, so depending on
what version of Cassandra you run this could impact you.

2) Indirect observation
You can keep an eye on metrics that healthy compaction will directly
contribute to. These include the number of sstables per read histogram,
estimated droppable tombstones, tombstones per read etc. You should keep an
eye on these things anyway as they can often show you areas where you can
fine tune compaction or your data model.

Everything exposed by nodetool is consumable via JMX which is great to plug
into your metrics/monitoring/observability system :)

On Mon, 13 Feb 2017 at 13:23 John Sanda <> wrote:

> What is a good way to determine whether or not compaction is falling
> behind? I read a couple things earlier that suggest nodetool
> compactionstats might not be the most reliable thing to use.
> - John
Ben Bromhead
CTO | Instaclustr <>
+1 650 284 9692
Managed Cassandra / Spark on AWS, Azure and Softlayer

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