On Mon, Dec 21, 2015 at 10:55 PM, Florian Haas <florian@xxxxxxxxxxx> wrote:
As stated above, yes. 64 shards.On Mon, Dec 21, 2015 at 3:35 PM, Haomai Wang <haomai@xxxxxxxx> wrote:
>
>
> On Fri, Dec 18, 2015 at 1:16 AM, Florian Haas <florian@xxxxxxxxxxx> wrote:
>>
>> Hey everyone,
>>
>> I recently got my hands on a cluster that has been underperforming in
>> terms of radosgw throughput, averaging about 60 PUTs/s with 70K
>> objects where a freshly-installed cluster with near-identical
>> configuration would do about 250 PUTs/s. (Neither of these values are
>> what I'd consider high throughput, but this is just to give you a feel
>> about the relative performance hit.)
>>
>> Some digging turned up that of the less than 200 buckets in the
>> cluster, about 40 held in excess of a million objects (1-4M), which
>> one bucket being an outlier with 45M objects. All buckets were created
>> post-Hammer, and use 64 index shards. The total number of objects in
>> radosgw is approx. 160M.
>>
>> Now this isn't a large cluster in terms of OSD distribution; there are
>> only 12 OSDs (after all, we're only talking double-digit terabytes
>> here). In almost all of these OSDs, the LevelDB omap directory has
>> grown to a size of 10-20 GB.
>>
>> So I have several questions on this:
>>
>> - Is it correct to assume that such a large LevelDB would be quite
>> detrimental to radosgw performance overall?
>>
>> - If so, would clearing that one large bucket and distributing the
>> data over several new buckets reduce the LevelDB size at all?
>>
>> - Is there even something akin to "ceph mon compact" for OSDs?
>>
>> - Are these large LevelDB databases a simple consequence of having a
>> combination of many radosgw objects and few OSDs, with the
>> distribution per-bucket being comparatively irrelevant?
>>
>> I do understand that the 45M object bucket itself would have been a
>> problem pre-Hammer, with no index sharding available. But with what
>> others have shared here, a rule of thumb of one index shard per
>> million objects should be a good one to follow, so 64 shards for 45M
>> objects doesn't strike me as totally off the mark. That's why I think
>> LevelDB I/O is actually the issue here. But I might be totally wrong;
>> all insights appreciated. :)
>
>
> Do you enable bucket index sharding?
> I'm not sure your bottleneck regard to your cluster, I guess you could
> disable leveldb compression to test whether reduce compaction influence.
Hmmm, you mean with "leveldb_compression = false"? Could you explain
why exactly *disabling* compression would help with large omaps?
Also, would "osd_compact_leveldb_on_mount" (undocumented) help here?
It looks to me like that is an option with no actual implementing
code, but I may be missing something.
The similarly named leveldb_compact_on_mount seems to only compact
LevelDB data in LevelDBStore. But I may be mistaken there too, as that
option also seems to be undocumented. Would configuring an osd with
leveldb_compact_on_mount=true do omap compaction on OSD daemon
startup, in a FileStore OSD?
I don't have exact info to sure this is the problem for your case, before I met this problem and because leveldb own single compaction thread which consume lots of time on compress/uncompress to do compaction.
what's your version, I guess "leveldb_compression" or "osd_leveldb_compression" can help
Cheers,
Florian
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Best Regards,
Wheat
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