CODEWITHSUNDEEP
cassandranosqlcassandra-2.0cassandra-3.0
LetsNoSQL
LetsNoSQL

Reputation: 1538

What does it mean by "Key cache save of system.KeyCache" on Opscenter?

I have running Cassandra cluster and opscenter too.I found that suddenly came "Key cache save of system.KeyCache" when I ran nodetool compactionstats. Also, found same on opscenter. Is there any performance impact due to this?

Upvotes: 0

Views: 147

Answers (1)

Chris Lohfink
Chris Lohfink

Reputation: 16410

The key cache saving reuses the compaction manager so it shows up in the current compaction tasks which will show up in compactionstats (and also opscenter). It shouldn't cause any performance issues but if it takes a real long time it might block regular compactions (if your concurrent compactions are lower) from completing.

This is really just so when a node starts up you don't have to wait for the key cache to warm up to improve read performance so not critical, and with a low hit rate may not be very meaningful. If they take a long time to save it may be that your data model has a ton of small partitions so the keycache has many entries that need to be serialized. In that case I would recommend setting key_cache_keys_to_save in your cassandra.yaml to something like 100, 1000 or something you can tune until your save time is more reasonable.

Upvotes: 1

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