Hi, sage. Thanks for your reply:-) Actually, our problem is as follows: we are trying to backup the rbd data in a ceph cluster which is cache-tier enabled using "rbd export-diff", however, due to the missing of some clone overlap, the export-diff operation can't be right. After debugging, we found that there are two reasons for this missing, one of which is as mentioned in this thread: http://tracker.ceph.com/issues/21072, which would led to the overlap recorded in the extensive attrs not to be "copied" to the base tier. And when we try to fix it, we found that the "_" policy is in our way, because the clone overlap is stored in "snapset" attr which has a non "_" prefixed name, and even if we modify the code to ignore the "_" policy when getting the extensive attrs, a "_" will be added when storing them into the base tier, which would make the following "list-snaps" operation not able to find the clone overlap. And the other reason that made the export-diff operate incorrectly is as described in http://tracker.ceph.com/issues/20896. To fix this, we are planning to add a "cache_clone_overlap" in SnapSet to track the cache stats while leaving the orignal "clone_overlap" to track modifications to the object. Is this the right way to go? By the way, last month, when trying to fix the bug: http://tracker.ceph.com/issues/17445, you asked for a test case in master branch to confirm that master doesn't have the same bug. I've submitted that test case in the PR: https://github.com/ceph/ceph/pull/17017 and cherry-pick it into PR: https://github.com/ceph/ceph/pull/16355. I'm very sorry for taking so long, I was very busy during the past month trying to solve the above problems. Could you help me review it when you are free, please? Thanks very much:-) On 24 August 2017 at 00:07, Sage Weil <sage@xxxxxxxxxxxx> wrote: > On Wed, 23 Aug 2017, Xuehan Xu wrote: >> Hi, everyone. >> >> In ReplicatedPG::_write_copy_chunk method, I saw the following code: >> >> if (!cop->temp_cursor.attr_complete) { >> t->touch(cop->results.temp_oid); >> for (map<string, bufferlist>::iterator p = cop->attrs.begin(); >> p != cop->attrs.end(); ++p) { >> cop->results.attrs[string("_") + p->first] = p->second; >> t->setattr(cop->results.temp_oid, string("_") + p->first, >> p->second); >> } >> cop->attrs.clear(); >> } >> >> It seems that user specified attrs are prefixed by "_", but why add >> "_" here, in ReplicatedPG::_write_copy_chunk? It seems that this >> method is used for copying objects in the RADOS cluster,. > > That is by design. The non-_ attributes are managed locally. > > In this case, the clone_overlap is not preserved because there is no code > to attempt to preserve it across the cache tier. (And blindly copying the > _ attribute wouldn't work.) > > I'm not sure what the issues would be with passing that metadata across > the promote and flush operations... I imagine it will be a bit fragile, > though. > > Is this something that is really worth fixing? > > sage > > >> >> On 23 August 2017 at 15:40, Xuehan Xu <xxhdx1985126@xxxxxxxxx> wrote: >> > It seems that when calling ReplicatedPG::getattrs_maybe_cache in >> > ReplicatedPG::fill_in_copy_get, "user_only" should be false. Is this >> > right? >> > >> > On 23 August 2017 at 15:25, Xuehan Xu <xxhdx1985126@xxxxxxxxx> wrote: >> >> I submitted an issue for this: >> >> http://tracker.ceph.com/issues/21072?next_issue_id=21071 >> >> >> >> On 23 August 2017 at 15:24, Xuehan Xu <xxhdx1985126@xxxxxxxxx> wrote: >> >>> Hi, everyone. >> >>> >> >>> Recently, we did a test as follows: >> >>> >> >>> We enabled cache tier and added a cache pool "vms_back_cache" on top >> >>> of the base pool "vms_back". we first created an object, and then >> >>> created a snap in the base pool and writing to that object again, >> >>> which would make the object be promoted into the cache pool. At this >> >>> time, we used "ceph-objectstore-tool" to dump the object, and the >> >>> result is as follows: >> >>> >> >>> { >> >>> "id": { >> >>> "oid": "test.obj.6", >> >>> "key": "", >> >>> "snapid": -2, >> >>> "hash": 750422257, >> >>> "max": 0, >> >>> "pool": 11, >> >>> "namespace": "", >> >>> "max": 0 >> >>> }, >> >>> "info": { >> >>> "oid": { >> >>> "oid": "test.obj.6", >> >>> "key": "", >> >>> "snapid": -2, >> >>> "hash": 750422257, >> >>> "max": 0, >> >>> "pool": 11, >> >>> "namespace": "" >> >>> }, >> >>> "version": "5010'5", >> >>> "prior_version": "4991'3", >> >>> "last_reqid": "client.175338.0:1", >> >>> "user_version": 5, >> >>> "size": 4194303, >> >>> "mtime": "2017-08-23 15:09:03.459892", >> >>> "local_mtime": "2017-08-23 15:09:03.461111", >> >>> "lost": 0, >> >>> "flags": 4, >> >>> "snaps": [], >> >>> "truncate_seq": 0, >> >>> "truncate_size": 0, >> >>> "data_digest": 4294967295, >> >>> "omap_digest": 4294967295, >> >>> "watchers": {} >> >>> }, >> >>> "stat": { >> >>> "size": 4194303, >> >>> "blksize": 4096, >> >>> "blocks": 8200, >> >>> "nlink": 1 >> >>> }, >> >>> "SnapSet": { >> >>> "snap_context": { >> >>> "seq": 13, >> >>> "snaps": [ >> >>> 13 >> >>> ] >> >>> }, >> >>> "head_exists": 1, >> >>> "clones": [ >> >>> { >> >>> "snap": 13, >> >>> "size": 4194303, >> >>> "overlap": "[0~100,115~4194188]" >> >>> } >> >>> ] >> >>> } >> >>> } >> >>> >> >>> Then we did cache-flush and cache-evict to flush that object down to >> >>> the base pool, and, again, used "ceph-objectstore-tool" to dump the >> >>> object in the base pool: >> >>> >> >>> { >> >>> "id": { >> >>> "oid": "test.obj.6", >> >>> "key": "", >> >>> "snapid": -2, >> >>> "hash": 750422257, >> >>> "max": 0, >> >>> "pool": 10, >> >>> "namespace": "", >> >>> "max": 0 >> >>> }, >> >>> "info": { >> >>> "oid": { >> >>> "oid": "test.obj.6", >> >>> "key": "", >> >>> "snapid": -2, >> >>> "hash": 750422257, >> >>> "max": 0, >> >>> "pool": 10, >> >>> "namespace": "" >> >>> }, >> >>> "version": "5015'4", >> >>> "prior_version": "4991'2", >> >>> "last_reqid": "osd.34.5013:1", >> >>> "user_version": 5, >> >>> "size": 4194303, >> >>> "mtime": "2017-08-23 15:09:03.459892", >> >>> "local_mtime": "2017-08-23 15:10:48.122138", >> >>> "lost": 0, >> >>> "flags": 52, >> >>> "snaps": [], >> >>> "truncate_seq": 0, >> >>> "truncate_size": 0, >> >>> "data_digest": 163942140, >> >>> "omap_digest": 4294967295, >> >>> "watchers": {} >> >>> }, >> >>> "stat": { >> >>> "size": 4194303, >> >>> "blksize": 4096, >> >>> "blocks": 8200, >> >>> "nlink": 1 >> >>> }, >> >>> "SnapSet": { >> >>> "snap_context": { >> >>> "seq": 13, >> >>> "snaps": [ >> >>> 13 >> >>> ] >> >>> }, >> >>> "head_exists": 1, >> >>> "clones": [ >> >>> { >> >>> "snap": 13, >> >>> "size": 4194303, >> >>> "overlap": "[]" >> >>> } >> >>> ] >> >>> } >> >>> } >> >>> >> >>> As is shown, the "overlap" field is empty. >> >>> In the osd log, we found the following records: >> >>> >> >>> 2017-08-23 12:46:36.083014 7f675c704700 20 osd.0 pg_epoch: 19 pg[3.3( >> >>> v 15'2 (0'0,15'2] local-les=15 n=2 ec=14 les/c/f 15/15/0 14/14/14) >> >>> [0,2,1] r=0 lpr=14 crt=0'0 lcod 15'1 mlcod 15'1 active+clean] got >> >>> attrs >> >>> 2017-08-23 12:46:36.083021 7f675c704700 15 >> >>> filestore(/home/xuxuehan/github-xxh-fork/ceph/src/dev/osd0) read >> >>> 3.3_head/#3:dd4db749:test-rados-api-xxh02v.ops.corp.qihoo.net-10886-3::foo:head# >> >>> 0~8 >> >>> 2017-08-23 12:46:36.083398 7f675c704700 10 >> >>> filestore(/home/xuxuehan/github-xxh-fork/ceph/src/dev/osd0) >> >>> FileStore::read >> >>> 3.3_head/#3:dd4db749:test-rados-api-xxh02v.ops.corp.qihoo.net-10886-3::foo:head# >> >>> 0~8/8 >> >>> 2017-08-23 12:46:36.083414 7f675c704700 20 osd.0 pg_epoch: 19 pg[3.3( >> >>> v 15'2 (0'0,15'2] local-les=15 n=2 ec=14 les/c/f 15/15/0 14/14/14) >> >>> [0,2,1] r=0 lpr=14 crt=0'0 lcod 15'1 mlcod 15'1 active+clean] got >> >>> data >> >>> 2017-08-23 12:46:36.083444 7f675c704700 20 osd.0 pg_epoch: 19 pg[3.3( >> >>> v 15'2 (0'0,15'2] local-les=15 n=2 ec=14 les/c/f 15/15/0 14/14/14) >> >>> [0,2,1] r=0 lpr=14 crt=0'0 lcod 15'1 mlcod 15'1 active+clean] >> >>> cursor.is_complete=0 0 attrs 8 bytes 0 omap header bytes 0 omap data >> >>> bytes in 0 keys 0 reqids >> >>> 2017-08-23 12:46:36.083457 7f675c704700 10 osd.0 pg_epoch: 19 pg[3.3( >> >>> v 15'2 (0'0,15'2] local-les=15 n=2 ec=14 les/c/f 15/15/0 14/14/14) >> >>> [0,2,1] r=0 lpr=14 crt=0'0 lcod 15'1 mlcod 15'1 active+clean] >> >>> dropping ondisk_read_lock >> >>> 2017-08-23 12:46:36.083467 7f675c704700 15 osd.0 pg_epoch: 19 pg[3.3( >> >>> v 15'2 (0'0,15'2] local-les=15 n=2 ec=14 les/c/f 15/15/0 14/14/14) >> >>> [0,2,1] r=0 lpr=14 crt=0'0 lcod 15'1 mlcod 15'1 active+clean] >> >>> do_osd_op_effects osd.0 con 0x7f67874f0d00 >> >>> 2017-08-23 12:46:36.083478 7f675c704700 15 osd.0 pg_epoch: 19 pg[3.3( >> >>> v 15'2 (0'0,15'2] local-les=15 n=2 ec=14 les/c/f 15/15/0 14/14/14) >> >>> [0,2,1] r=0 lpr=14 crt=0'0 lcod 15'1 mlcod 15'1 active+clean] >> >>> log_op_stats osd_op(osd.0.6:2 3.92edb2bb >> >>> test-rados-api-xxh02v.ops.corp >> >>> >> >>> It seems that, when doing "copy-get", no extensive attributes are >> >>> copied. We believe that it's the following code that led to this >> >>> result: >> >>> >> >>> int ReplicatedPG::getattrs_maybe_cache(ObjectContextRef obc, >> >>> map<string, bufferlist> *out, >> >>> bool user_only) { >> >>> int r = 0; >> >>> if (pool.info.require_rollback()) { >> >>> if (out) >> >>> *out = obc->attr_cache; >> >>> } else { >> >>> r = pgbackend->objects_get_attrs(obc->obs.oi.soid, out); >> >>> } >> >>> if (out && user_only) { >> >>> map<string, bufferlist> tmp; >> >>> for (map<string, bufferlist>::iterator i = out->begin(); >> >>> i != out->end(); ++i) { >> >>> if (i->first.size() > 1 && i->first[0] == '_') >> >>> tmp[i->first.substr(1, i->first.size())].claim(i->second); >> >>> } >> >>> tmp.swap(*out); >> >>> } >> >>> return r; >> >>> } >> >>> >> >>> It seems that when "user_only" is true, extensive attributes without a >> >>> '_' as the starting character in its name would be filtered out. Is it >> >>> supposed to be doing things in this way? >> >>> And we found that there are only two places in the source code that >> >>> invoked ReplicatedPG::getattrs_maybe_cache, in both of which >> >>> "user_only" is true. Why add this parameter? >> >>> >> >>> By the way, we also found that these codes are added in commit >> >>> 78d9c0072bfde30917aea4820a811d7fc9f10522, but we don't understand the >> >>> purpose of it. >> >>> >> >>> Thank you:-) >> -- >> To unsubscribe from this list: send the line "unsubscribe ceph-devel" in >> the body of a message to majordomo@xxxxxxxxxxxxxxx >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> >> -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
