Yes, it give a small but significant to performance hit. But it's necessary and may exists optimization space. On Wed, Dec 3, 2014 at 4:58 PM, Andreas Bluemle <andreas.bluemle@xxxxxxxxxxx> wrote: > 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 -- Best Regards, Wheat -- 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
