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From Luke Jolly <>
Subject Approximate row count
Date Wed, 27 Jul 2016 18:44:30 GMT
I have a table that I'm storing ad impression data in with every row being
an impression.  I want to get a count of total rows / impressions.  I know
that there is in the ball park of 200-400 million rows in this table and
from my reading "Number of keys" in the output of cfstats should be a
reasonably accurate estimate. However, it is 39434. Am I misunderstanding
something? Every node in my cluster has a complete copy of the keyspace.

		Table: impressions_2
		SSTable count: 22
		Space used (live): 51255709817
		Space used (total): 51255709817
		Space used by snapshots (total): 49415721741
		Off heap memory used (total): 30824975
		SSTable Compression Ratio: 0.20347134631246266
		Number of keys (estimate): 39434
		Memtable cell count: 18279
		Memtable data size: 15897457
		Memtable off heap memory used: 0
		Memtable switch count: 1294
		Local read count: 347016
		Local read latency: 12.573 ms
		Local write count: 109226238
		Local write latency: 0.023 ms
		Pending flushes: 0
		Bloom filter false positives: 655
		Bloom filter false ratio: 0.00000
		Bloom filter space used: 97552
		Bloom filter off heap memory used: 97376
		Index summary off heap memory used: 26719
		Compression metadata off heap memory used: 30700880
		Compacted partition minimum bytes: 311
		Compacted partition maximum bytes: 386857368
		Compacted partition mean bytes: 6424107
		Average live cells per slice (last five minutes): 1027.9502011434631
		Maximum live cells per slice (last five minutes): 5722
		Average tombstones per slice (last five minutes): 1.0
		Maximum tombstones per slice (last five minutes): 1

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