We are using cassandra 2.0.17 and we have a table with 50% selects, 40% of updates and 10% of inserts (no deletes).
To have high read performance for such table we found that it is suggested to use LeveledCompactionStrategy (it is supposed to guarantee that 99% of reads will be fulfilled from single SSTable). Every day when I run nodetool cfhistograms i see more and more SSTtables per read. First day we had 1, than we had 1,2,3 ...
and this morning I am seeing this:
ubuntu@ip:~$ nodetool cfhistograms prodb groups | head -n 20
prodb/groups histograms
SSTables per Read
1 sstables: 27007
2 sstables: 97694
3 sstables: 95239
4 sstables: 3928
5 sstables: 14
6 sstables: 0
7 sstables: 19
The describe groups returns this:
CREATE TABLE groups (
...
) WITH
bloom_filter_fp_chance=0.010000 AND
caching='KEYS_ONLY' AND
comment='' AND
dclocal_read_repair_chance=0.100000 AND
gc_grace_seconds=172800 AND
index_interval=128 AND
read_repair_chance=0.000000 AND
replicate_on_write='true' AND
populate_io_cache_on_flush='false' AND
default_time_to_live=0 AND
speculative_retry='99.0PERCENTILE' AND
memtable_flush_period_in_ms=0 AND
compaction={'class': 'LeveledCompactionStrategy'} AND
compression={'sstable_compression': 'LZ4Compressor'};
Is it normal? In such case we loose the advantage of using LeveledCompaction which as described in the documentation should guarantee 99% of reads from single sstable.