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From André Cruz <andre.c...@co.sapo.pt>
Subject Row cache and counters
Date Sat, 29 Dec 2012 11:14:36 GMT
Hello.

I recently was having some timeout issues while updating counters and turned on row cache
for that particular CF. This is its stats:

		Column Family: UserQuotas
		SSTable count: 3
		Space used (live): 2687239
		Space used (total): 2687239
		Number of Keys (estimate): 22912
		Memtable Columns Count: 25766
		Memtable Data Size: 180975
		Memtable Switch Count: 17
		Read Count: 356900
		Read Latency: 1.004 ms.
		Write Count: 548996
		Write Latency: 0.045 ms.
		Pending Tasks: 0
		Bloom Filter False Postives: 17
		Bloom Filter False Ratio: 0.00000
		Bloom Filter Space Used: 44232
		Compacted row minimum size: 125
		Compacted row maximum size: 770
		Compacted row mean size: 308

Since it is rather small I was hoping that it would eventually be all cached, and the timeouts
would go away. I'm updating the counters with a CL of ONE, so I thought that the timeout would
be caused by the read step and the cache would help here. But I still get timeouts, and the
cache hit rate is rather low:

Row Cache        : size 1436291 (bytes), capacity 524288000 (bytes), 125310 hits, 442760 requests,
0.247 recent hit rate, 0 save period in seconds

Am I assuming something wrong about the row cache? Isn't it updated when a counter update
occurs or is just invalidated?

Best regards,
André Cruz
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