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From Omid Aladini <omidalad...@gmail.com>
Subject Reduced key-cache due to memory pressure and cache size estimate
Date Wed, 11 Jul 2012 10:37:09 GMT
Hi,

I'm trying to tune, memtable size, key cache size and heap size on
Cassandra 1.1.0 but I keep having memory pressure and reduced cache size.
With the following settings:

heap size: 10GB (had the same issue with 8GB so I'm testing with increased
heap size)
memtable_total_space_in_mb: 2GB
key_cache_size_in_mb: 2GB   (global key cache capacity)

Still, heap usage hits flush_largest_memtables_at (= 0.75) many times in a
short period of time before hitting reduce_cache_sizes_at (= 0.85) that
reduces the cache size and resolves memory pressure.

In one instance, cache size is reported to be 1450MB before reduction and
~870MB after reduction, but the gain in heap space due to reduction in
cache size is about 3GB.

Could it be that the cache size estimate in megabytes isn't accurate?

Thanks,
Omid

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