Dnia 2020-06-18, o godz. 10:51:31 Simon Leinen <simon.leinen@switch.ch> napisał(a):
Dear Mariusz,
we're using Ceph as S3-compatible storage to serve static files (mostly css/js/images + some videos) and I've noticed that there seem to be huge read amplification for index pool.
we have observed that too, under Nautilus (14.2.4-14.2.8).
Incoming traffic magniture is of around 15k req/sec (mostly sub 1MB request but index pool is getting hammered:
pool pl-war1.rgw.buckets.index id 10 client io 632 MiB/s rd, 277 KiB/s wr, 129.92k op/s rd, 415 op/s wr
pool pl-war1.rgw.buckets.data id 11 client io 4.5 MiB/s rd, 6.8 MiB/s wr, 640 op/s rd, 1.65k op/s wr
and is getting order of magnitude more requests
Our hypothesis is that this is due to the way that RadosGW maps bucket index queries (ListObjects/ListObjectsV2) to Rados-level operations against a *sharded* index.
For certain types of S3 index queries, the response must be collected from multiple (potentially all) shards of the index.
S3 index queries are always "bounded" by the response limitation (1000 keys by default). But when your index is distributed over, let's say, 2000 shards, RadosGW must collect some data from those 2000 shards, then throw away most of what it gets, and return the next 1000 keys. This could explain the kind of read amplification that you are seeing.
(In practice, S3 index queries often use "prefix" and "delimiter" to emulate a hierarchical directory structure. A recently merged change, https://github.com/ceph/ceph/pull/30272 , should make such queries much more efficient in RadosGW (note that the change contains some extensions to the OSD-side Rados protocol). But if I read it correctly, that change is already in the version you are using.)
listing itself is bugged in version I'm running: https://tracker.ceph.com/issues/45955 But yes, our structure is generally /bucket/prefix/prefix/file so there is not many big directories (we're migrating from GFS where that was a problem)
Paul Emmerich has written about performance issues with large buckets on this list, see https://lists.ceph.io/hyperkitty/list/dev@ceph.io/thread/36P62BOOCJBVVJCVUX5...
Let's say that there are opportunities for further improvements.
You could look for the specific queries that cause the high read load in your system. Maybe there's something that can be done on the client side. This could also provide input for Ceph development as to what kinds of index operations are used by applications "in the wild". Those might be worth optimizing first :-)
Is there a way to debug which query exactly is causing that ? Currently there is a lot of incoming traffic (mostly from aws cli sync) as we're migrating data over but that's at most hundreds of requests per sec.
running 15.2.3, nothing special in terms of tunning aside from disabling some logging as to not overflow the logs.
We've had similar test cluster on 12.x (and way slower hardware) getting similar traffic and haven't observed that magnitude of difference.
Was your bucket index sharded in 12.x?
we didn't touch default settings so I assume not ? "radosgw-admin metadata get" and "radosgw-admin bucket stat" doesn't say anything about shards on old cluster, while on new cluster there is from 11 to few hundred on the biggest buckets.
when enabling debug on affected OSD I only get spam of
2020-06-17T12:35:05.700+0200 7f80694c4700 10 bluestore(/var/lib/ceph/osd/ceph-20) omap_get_header 10.51_head oid #10:8b1a34d8:::.dir.88d4f221-0da5-444d-81a8-517771278350.454759.8.214:head# = 0 2020-06-17T12:35:05.700+0200 7f80694c4700 10 bluestore(/var/lib/ceph/osd/ceph-20) get_omap_iterator 10.51_head #10:8b1a34d8:::.dir.88d4f221-0da5-444d-81a8-517771278350.454759.8.214:head# 2020-06-17T12:35:05.700+0200 7f80694c4700 10 bluestore(/var/lib/ceph/osd/ceph-20) get_omap_iterator 10.51_head #10:8b1a34d8:::.dir.88d4f221-0da5-444d-81a8-517771278350.454759.8.214:head# 2020-06-17T12:35:05.700+0200 7f80694c4700 10 bluestore(/var/lib/ceph/osd/ceph-20) get_omap_iterator 10.51_head #10:8b1a34d8:::.dir.88d4f221-0da5-444d-81a8-517771278350.454759.8.214:head# 2020-06-17T12:35:05.700+0200 7f80694c4700 10 bluestore(/var/lib/ceph/osd/ceph-20) get_omap_iterator 10.51_head #10:8b1a34d8:::.dir.88d4f221-0da5-444d-81a8-517771278350.454759.8.214:head# 2020-06-17T12:35:05.704+0200 7f80694c4700 10 bluestore(/var/lib/ceph/osd/ceph-20) get_omap_iterator 10.51_head #10:8b1a34d8:::.dir.88d4f221-0da5-444d-81a8-517771278350.454759.8.214:head# 2020-06-17T12:35:05.704+0200 7f80694c4700 10 bluestore(/var/lib/ceph/osd/ceph-20) get_omap_iterator 10.51_head #10:8b1a34d8:::.dir.88d4f221-0da5-444d-81a8-517771278350.454759.8.214:head# 2020-06-17T12:35:05.704+0200 7f80694c4700 10 bluestore(/var/lib/ceph/osd/ceph-20) get_omap_iterator 10.51_head #10:8b1a34d8:::.dir.88d4f221-0da5-444d-81a8-517771278350.454759.8.214:head# 2020-06-17T12:35:05.704+0200 7f80694c4700 10 bluestore(/var/lib/ceph/osd/ceph-20) get_omap_iterator 10.51_head #10:8b1a34d8:::.dir.88d4f221-0da5-444d-81a8-517771278350.454759.8.214:head# 2020-06-17T12:35:05.704+0200 7f80694c4700 10 bluestore(/var/lib/ceph/osd/ceph-20) omap_get_header 10.51_head oid #10:8b0d75b0:::.dir.88d4f221-0da5-444d-81a8-517771278350.454759.8.222:head# = 0 2020-06-17T12:35:05.704+0200 7f80694c4700 10 bluestore(/var/lib/ceph/osd/ceph-20) get_omap_iterator 10.51_head #10:8b0d75b0:::.dir.88d4f221-0da5-444d-81a8-517771278350.454759.8.222:head# 2020-06-17T12:35:05.704+0200 7f80694c4700 10 bluestore(/var/lib/ceph/osd/ceph-20) get_omap_iterator 10.51_head #10:8b0d75b0:::.dir.88d4f221-0da5-444d-81a8-517771278350.454759.8.222:head# 2020-06-17T12:35:05.704+0200 7f80694c4700 10 bluestore(/var/lib/ceph/osd/ceph-20) get_omap_iterator 10.51_head #10:8b0d75b0:::.dir.88d4f221-0da5-444d-81a8-517771278350.454759.8.222:head# 2020-06-17T12:35:05.704+0200 7f80694c4700 10 bluestore(/var/lib/ceph/osd/ceph-20) get_omap_iterator 10.51_head #10:8b0d75b0:::.dir.88d4f221-0da5-444d-81a8-517771278350.454759.8.222:head# 2020-06-17T12:35:05.704+0200 7f80694c4700 10 bluestore(/var/lib/ceph/osd/ceph-20) get_omap_iterator 10.51_head #10:8b0d75b0:::.dir.88d4f221-0da5-444d-81a8-517771278350.454759.8.222:head# 2020-06-17T12:35:05.704+0200 7f80694c4700 10 bluestore(/var/lib/ceph/osd/ceph-20) get_omap_iterator 10.51_head #10:8b0d75b0:::.dir.88d4f221-0da5-444d-81a8-517771278350.454759.8.222:head# 2020-06-17T12:35:05.708+0200 7f80694c4700 10 bluestore(/var/lib/ceph/osd/ceph-20) get_omap_iterator 10.51_head #10:8b0d75b0:::.dir.88d4f221-0da5-444d-81a8-517771278350.454759.8.222:head# 2020-06-17T12:35:05.708+0200 7f80694c4700 10 bluestore(/var/lib/ceph/osd/ceph-20) get_omap_iterator 10.51_head #10:8b0d75b0:::.dir.88d4f221-0da5-444d-81a8-517771278350.454759.8.222:head# 2020-06-17T12:35:05.716+0200 7f806d4cc700 10 bluestore(/var/lib/ceph/osd/ceph-20) omap_get_header 10.51_head oid #10:8b5ed205:::.dir.88d4f221-0da5-444d-81a8-517771278350.454759.8.151:head# = 0 2020-06-17T12:35:05.716+0200 7f806d4cc700 10 bluestore(/var/lib/ceph/osd/ceph-20) get_omap_iterator 10.51_head #10:8b5ed205:::.dir.88d4f221-0da5-444d-81a8-517771278350.454759.8.151:head# 2020-06-17T12:35:05.716+0200 7f806d4cc700 10 bluestore(/var/lib/ceph/osd/ceph-20) get_omap_iterator 10.51_head #10:8b5ed205:::.dir.88d4f221-0da5-444d-81a8-517771278350.454759.8.151:head# 2020-06-17T12:35:05.720+0200 7f806d4cc700 10 bluestore(/var/lib/ceph/osd/ceph-20) get_omap_iterator 10.51_head #10:8b5ed205:::.dir.88d4f221-0da5-444d-81a8-517771278350.454759.8.151:head# 2020-06-17T12:35:05.720+0200 7f806d4cc700 10 bluestore(/var/lib/ceph/osd/ceph-20) get_omap_iterator 10.51_head #10:8b5ed205:::.dir.88d4f221-0da5-444d-81a8-517771278350.454759.8.151:head# 2020-06-17T12:35:05.720+0200 7f806d4cc700 10 bluestore(/var/lib/ceph/osd/ceph-20) get_omap_iterator 10.51_head #10:8b5ed205:::.dir.88d4f221-0da5-444d-81a8-517771278350.454759.8.151:head# 2020-06-17T12:35:05.720+0200 7f806d4cc700 10 bluestore(/var/lib/ceph/osd/ceph-20) get_omap_iterator 10.51_head #10:8b5ed205:::.dir.88d4f221-0da5-444d-81a8-517771278350.454759.8.151:head# 2020-06-17T12:35:05.720+0200 7f806d4cc700 10 bluestore(/var/lib/ceph/osd/ceph-20) get_omap_iterator 10.51_head #10:8b5ed205:::.dir.88d4f221-0da5-444d-81a8-517771278350.454759.8.151:head# 2020-06-17T12:35:05.720+0200 7f806d4cc700 10 bluestore(/var/lib/ceph/osd/ceph-20) get_omap_iterator 10.51_head #10:8b5ed205:::.dir.88d4f221-0da5-444d-81a8-517771278350.454759.8.151:head#
Hm, I don't understand enough about the operations that this represents, but maybe one of the RadosGW developers can explain why a single OSD would perform so many similar requests in such a short timeframe.
I'm getting similar logs on any osd/pg that takes part in the .index Cheers -- Mariusz Gronczewski (XANi) <xani666@gmail.com> GnuPG: 0xEA8ACE64 http://devrandom.pl