The space calculation counters in column family had two problem:
1. The total bytes is an ever growing counter, which is meaningless for
the API.
2. Trying to simply sum the size on all shards, ignores the fact that the
same sstable file can be referenced by multiple shards, this is
especially noticeable during migration time.
To solve this, the implementation was modified so instead of
collecting the sizes, the API would collect a map of file name to size
and then would do the summing.
This removes the duplications and fixes the total bytes calculation
Calling cfstats before the change with load after a compaction happend:
$ nodetool cfstats keyspace1
Keyspace: keyspace1
Verify write latency 1068253.0 76435
Read Count: 75915
Read Latency: 0.5953986037015082 ms.
Write Count: 76435
Write Latency: 0.013975966507490025 ms.
Pending Flushes: 0
Table: standard1
SSTable count: 5
Space used (live): 44261215
Space used (total): 219724478
After the fix:
$ nodetool cfstats keyspace1
Keyspace: keyspace1
Verify write latency 1863206.0 124219
Read Count: 125401
Read Latency: 0.9381053978835895 ms.
Write Count: 124219
Write Latency: 0.01499936402643718 ms.
Pending Flushes: 0
Table: standard1
SSTable count: 6
Space used (live): 50402904
Space used (total): 50402904
Space used by snapshots (total): 0
Fixes: #1042
Signed-off-by: Amnon Heiman <amnon@scylladb.com>
Message-Id: <1464518757-14666-2-git-send-email-amnon@scylladb.com>
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