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From Tom van den Berge <...@drillster.com>
Subject Unexplainably large reported partition sizes
Date Fri, 04 Mar 2016 13:56:38 GMT
Hi,

I'm seeing warnings in my logs about compacting large partitions, e.g.:

 Compacting large partition
drillster/subscriberstats:rqtPewK-1chi0JSO595u-Q (1,470,058,292 bytes)

This means that this single partition is about 1.4GB large. This is much
larger that it can possibly be, because of two reasons:
  1) the partition has appr. 50K rows, each roughly 62 bytes = ~3 MB
  2) the entire table consumes appr. 500MB of disk space on the node
containing the partition (including snapshots)

Furthermore, nodetool cfstats tells me this:
Space used (live): 253,928,111
Space used (total): 253,928,111
Compacted partition maximum bytes: 2,395,318,855
The space used seem to match the actual size (excl. snapshots), but the
Compacted partition maximum bytes (2,3 GB) seems to be far higher than
possible. Does anyone know how it is possible that Cassandra reports such
unlikely sizes?

>From time to time, I'm noticing relatively bad latencies when such
partitions are (fully) queried. So I'm not fully convinced that the actual
partition size is not in the order of 1 or 2 GB. Does anyone have an
explanation for these discrepancies?

Thanks,
Tom

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