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From Peter Schuller <>
Subject Re: Cassandra GC Settings
Date Mon, 17 Jan 2011 21:33:41 GMT
> Now, a full stop of the application was what I was seeing extensively before
> (100-200 times over the course of a major compaction as reported by
> gossipers on other nodes). I have also just noticed that the previous
> instability (ie application stops) correlated with the compaction of a few
> column families characterized by fairly fat rows (10 mb mean size, max sizes
> 150-200 mb, up to a million+ columns per row). My theory is that each row
> being compacted with the old settings was being promoted to the old
> generation, thereby running the heap out of space and causing a stop the
> world gc. With the new settings, rows being compacted typically remain in
> the young generation, allowing them to be cleaned up more quickly with less
> effort on the part of the garbage collector. Does this theory sound
> reasonable?

Sounds reasonable I think. In addition to sizing the young gen, decreasing:

   in_memory_compaction_limit_in_mb: 64

from the default of 64 might help here I suppose.

/ Peter Schuller

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