On 07/30/2014 08:46 PM, Shu, Xinxin wrote:
Hi mark,
Which way do you used to set a higher limitation? use 'ulimit' command or
enlarge rocksdb_max_open_files config option?
ulimit command, though you might be able to limit the max open files in
rocksdb to be smaller than the default too. Setting a higher ulimit is
what we already do for ceph processes so I just mimicked our existing
solution.
Cheers,
xinxin
-----Original Message-----
From: Mark Nelson [mailto:mark.nel...@inktank.com]
Sent: Thursday, July 31, 2014 1:35 AM
To: Shu, Xinxin; ceph-devel@vger.kernel.org
Subject: Re: First attempt at rocksdb monitor store stress testing
Hi Xinxin,
Yes, that did work. I was able to observe the log and figure out the
stall: Too many files open in the level0->level1 compaction thread.
Similar to the issue that we've seen the past with leveldb. Setting a higher
ulimit fixed the problem. With leveled compaction on spinning disks I do see
latency spikes but at first glance they do not appear to be as bad as with
leveldb. I will now run some longer tests.
Mark
On 07/27/2014 11:45 PM, Shu, Xinxin wrote:
Hi mark,
I tested this option on my setup , same issue happened , I will dig into it ,
if you want to get info log , there is a workaround, set this option to none:
Rocksdb_log = ""
Cheers,
xinxin
-----Original Message-----
From: Mark Nelson [mailto:mark.nel...@inktank.com]
Sent: Saturday, July 26, 2014 12:10 AM
To: Shu, Xinxin; ceph-devel@vger.kernel.org
Subject: Re: First attempt at rocksdb monitor store stress testing
Hi Xinxin,
I'm trying to enable the rocksdb log file as described in config_opts using:
rocksdb_log = <path to log file>
The file gets created but is empty. Any ideas?
Mark
On 07/24/2014 08:28 PM, Shu, Xinxin wrote:
Hi mark,
I am looking forward to your results on SSDs .
rocksdb generates a crc of data to be written , this cannot be switch off (but
can be subsititued with xxhash), there are two options , Option.
verify_checksums_in_compaction and ReadOptions. verify_checksums, If we
disable these two options , i think cpu usage will goes down . If we use
universal compaction , this is not friendly with read operation.
Btw , can you list your rocksdb configuration?
Cheers,
xinxin
-----Original Message-----
From: Mark Nelson [mailto:mark.nel...@inktank.com]
Sent: Friday, July 25, 2014 7:45 AM
To: Shu, Xinxin; ceph-devel@vger.kernel.org
Subject: Re: First attempt at rocksdb monitor store stress testing
Earlier today I modified the rocksdb options so I could enable universal
compaction. Over all performance is lower but I don't see the hang/stall in
the middle of the test either. Instead the disk is basically pegged with 100%
writes. I suspect average latency is higher than leveldb, but the highest
latency is about 5-6s while we were seeing 30s spikes for leveldb with levelled
(heh) compaction.
I haven't done much tuning either way yet. It may be that if we keep level 0
and level 1 roughly the same size we can reduce stalls in the levelled setups.
It will also be interesting to see what happens in these tests on SSDs.
Mark
On 07/24/2014 06:13 AM, Mark Nelson wrote:
Hi Xinxin,
Thanks! I wonder as well if it might be interesting to expose the
options related to universal compaction? It looks like rocksdb
provides a lot of interesting knobs you can adjust!
Mark
On 07/24/2014 12:08 AM, Shu, Xinxin wrote:
Hi mark,
I think this maybe related to 'verify_checksums' config option
,when ReadOptions is initialized, default this option is true ,
all data read from underlying storage will be verified against
corresponding checksums, however, this option cannot be
configured in wip-rocksdb branch. I will modify code to make this option
configurable .
Cheers,
xinxin
-----Original Message-----
From: ceph-devel-ow...@vger.kernel.org
[mailto:ceph-devel-ow...@vger.kernel.org] On Behalf Of Mark Nelson
Sent: Thursday, July 24, 2014 7:14 AM
To: ceph-devel@vger.kernel.org
Subject: First attempt at rocksdb monitor store stress testing
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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