On Fri, Aug 14, 2015 at 7:23 PM, Alexander Korotkov <aekorot...@gmail.com> wrote: > > On Thu, Aug 6, 2015 at 1:01 PM, Ildus Kurbangaliev < i.kurbangal...@postgrespro.ru> wrote: >> >> >> I've looked deeper and I found PgBackendStatus to be not a suitable >> place for keeping information about low level waits. Really, PgBackendStatus >> is used to track high level information about backend. This is why auxiliary >> processes don't have PgBackendStatus, because they don't have such information >> to expose. But when we come to the low level wait events then auxiliary >> processes are as useful for monitoring as backends are. WAL writer, >> checkpointer, bgwriter etc are using LWLocks as well. This is certainly unclear >> why they can't be monitored. >> >> This is why I think we shoudn't place wait event into PgBackendStatus. It >> could be placed into PGPROC or even separate data structure with different >> concurrency model which would be most suitable for monitoring. > > > +1 for tracking wait events not only for backends > > Ildus, could you do following? > 1) Extract LWLocks refactoring into separate patch. > 2) Make a patch with storing current wait event information in PGPROC. >
Now as Robert has committed standardization of lwlock names in commit - aa65de04, let us try to summarize and work on remaining parts of the patch. So I think now the next set of work is as follows: 1. Modify the tranche mechanism so that information about LWLocks can be tracked easily. For this already there is some discussion, ideas and initial patch is floated in this thread and there doesn't seem to be much conflicts, so we can write the patch for it. I am planning to write or modify the existing patch unless you, IIdus or anyone has objections or want to write it, please let me know to avoid duplication of work. 2. Track wait_event in pg_stat_activity. Now here the main point where we doesn't seem to be in complete agreement is that shall we keep it as one byte in PgBackendStatus or use two or more bytes to store wait_event information and still there is another point made by you to store it in PGProc rather than in PgBackendStatus so that we can display information of background processes as well. Now as a matter of consensus, I think Tom has raised a fair point [1] against storing this information in PGProc and I feel that it is relatively less important to have such information about background processes and the reason for same is explained upthread [2]. About having more than one-byte to store information about various wait_events, I think now we will not have more than 100 or so events to track, do you really think that anytime in forseeable future we will have more than 256 important events which we would like to track? So I think about this lets first try to build the consensus and then attempt to write or modify the patch. [1] - http://www.postgresql.org/message-id/4067.1439561...@sss.pgh.pa.us [2] - http://www.postgresql.org/message-id/CAA4eK1JRQGTgRMRao6H65rA=fhifucnqhx7ongy58um6rn1...@mail.gmail.com With Regards, Amit Kapila. EnterpriseDB: http://www.enterprisedb.com
