Hi Guys,
So I've been interested lately in leveldb 99th percentile latency (and
the amount of write amplification we are seeing) with leveldb. Joao
mentioned he has written a tool called mon-store-stress in
wip-leveldb-misc to try to provide a means to roughly guess at what's
happening on the mons under heavy load. I cherry-picked it over to
wip-rocksdb and after a couple of hacks was able to get everything built
and running with some basic tests. There was little tuning done and I
don't know how realistic this workload is, so don't assume this means
anything yet, but some initial results are here:
http://nhm.ceph.com/mon-store-stress/First%20Attempt.pdf
Command that was used to run the tests:
./ceph-test-mon-store-stress --mon-keyvaluedb <leveldb|rocksdb>
--write-min-size 50K --write-max-size 2M --percent-write 70
--percent-read 30 --keep-state --test-seed 1406137270 --stop-at 5000 foo
The most interesting bit right now is that rocksdb seems to be hanging
in the middle of the test (left it running for several hours). CPU
usage on one core was quite high during the hang. Profiling using perf
with dwarf symbols I see:
- 49.14% ceph-test-mon-s ceph-test-mon-store-stress [.] unsigned int
rocksdb::crc32c::ExtendImpl<&rocksdb::crc32c::Fast_CRC32>(unsigned int,
char const*, unsigned long)
- unsigned int
rocksdb::crc32c::ExtendImpl<&rocksdb::crc32c::Fast_CRC32>(unsigned int,
char const*, unsigned long)
51.70% rocksdb::ReadBlockContents(rocksdb::RandomAccessFile*,
rocksdb::Footer const&, rocksdb::ReadOptions const&,
rocksdb::BlockHandle const&, rocksdb::BlockContents*, rocksdb::Env*, bool)
48.30%
rocksdb::BlockBasedTableBuilder::WriteRawBlock(rocksdb::Slice const&,
rocksdb::CompressionType, rocksdb::BlockHandle*)
Not sure what's going on yet, may need to try to enable
logging/debugging in rocksdb. Thoughts/Suggestions welcome. :)
Mark
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