Hi Gregory, On Tue, 2 Dec 2014 10:32:50 -0800 Gregory Farnum <greg@xxxxxxxxxxx> wrote: > On Tue, Dec 2, 2014 at 10:17 AM, Andreas Bluemle > <andreas.bluemle@xxxxxxxxxxx> wrote: > > Hi, > > > > during code profiling using LTTng, I encounter that during > > processing of write requests to the cluster, the ceph-osd > > spends a lot of time in the ReplicatedPG::log_operation > > before the the actual writes to journal and object > > in the FileStore are triggered. > > > > This happens in ReplicatedBackend::submit_transaction. > > > > What I wonder is > > - what is the purpose of the log_operation? > > If I am not mistaken, then it is neither the write-to-journal > > nor the write-to-object; both of these are triggered from > > the queue_operation following that log_operation. > > This is setting up the changes to the pg log, and encoding them into > the transaction. > > > - can the sequence between the log_operation and > > the actual queue_operation be reversed in > > ReplicatedBackend::submit_transaction? > > Nope, it needs to go into the transaction and get journaled. > I'm kind of surprised this is a big time sink, but there is a lot of > encoding so if you're running against a fast system I suppose it could > be relatively large. >From what I see on my test system, adding the pg log entry consumes about 60 microseconds - which is about 12 % of the overall time spent for a write request on a replicating OSD, which is sth. like 460 microseconds between receipt of the MSG_OSD_SUBOP at the messenger until the corresponding MSG_OSD_SUBOPREPLY is sent back to the primary OSD. > -Greg > -- > 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 > > -- Andreas Bluemle mailto:Andreas.Bluemle@xxxxxxxxxxx ITXperts GmbH http://www.itxperts.de Balanstrasse 73, Geb. 08 Phone: (+49) 89 89044917 D-81541 Muenchen (Germany) Fax: (+49) 89 89044910 Company details: http://www.itxperts.de/imprint.htm -- 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
