On Thu, Mar 13, 2014 at 3:56 PM, Greg Poirier <greg.poirier@xxxxxxxxxx> wrote: > We've been seeing this issue on all of our dumpling clusters, and I'm > wondering what might be the cause of it. > > In dump_historic_ops, the time between op_applied and sub_op_commit_rec or > the time between commit_sent and sub_op_applied is extremely high. Some of > the osd_sub_ops are as long as 100 ms. A sample dump_historic_ops is > included at the bottom. It's important to understand what each of those timestamps are reporting. op_applied: the point at which an OSD has applied an operation to its readable backing filesystem in-memory (which for xfs or ext4 will be after it's committed to the journal) sub_op_commit_rec: the point at which an OSD has gotten commits from the replica OSDs commit_sent: the point at which a replica OSD has sent a commit back to its primary sub_op_applied: the point at which a replica OSD has applied a particular operation to its backing filesystem in-memory (again, after the journal if using xfs) Reads are never served from replicas, so a long time between commit_sent and sub_op_applied should not in itself be an issue. A lag time between op_applied and sub_op_commit_rec means that the OSD is waiting on its replicas. A long time there indicates either that the replica is processing slowly, or that there's some issue in the communications stack (all the way from the raw ethernet up to the message handling in the OSD itself). So the first thing to look for are sub ops which have a lag time between the received_at and commit_sent timestamps. If none of those ever turn up, but unusually long waits for sub_op_commit_rec are still present, then it'll take more effort to correlate particular subops on replicas with the op on the primary they correspond to, and see where the time lag is coming into it. -Greg Software Engineer #42 @ http://inktank.com | http://ceph.com _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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