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I have a Cassandra cluster running for quite some time now (months) and, as expected, it has been consuming large quantities of data every day.

In the past few days the cluster has been having problems because one of the nodes keeps crashing and I don't see much in the logs.

One thing that stands out is the following warning but I'm now sure if it is related:

insufficient space to compact all requested files. 846201.56MB required

which is quite more than it is available. Nevertheless, even if there was enough disk to support such compaction, it seems excessive, doesn't it?

Does anyone have any idea what my problem is?

thank you for your attention.

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By default, Cassandra uses SizeTieredCompactionStrategy that compacts several files (4 by default) of similar size into bigger file. These files contain multiple partitions, so big file size isn't a necessary sign of wide partitions.

When you're using Cassandra (especially with SizeTieredCompactionStrategy) you need to have ~50% of disk space free so Cassandra will able to write data during compaction - after compaction happens, the old files will be removed.

You may also consider the use of other compaction strategies, such as, LeveledCompactionStrategy, but it's more suited for read-heavy workloads (like 90% of all operations are reads).

You can read more about compaction strategies in documentation, and about size tiered compaction in this blog post.

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