Re: New statistics for WAL buffer dirty writes

What happened to this patch?  We were waiting on an updated version from
you.


Satoshi Nagayasu wrote:
> (2012/12/10 3:06), Tomas Vondra wrote:
> >On 29.10.2012 04:58, Satoshi Nagayasu wrote:
> >>2012/10/24 1:12, Alvaro Herrera wrote:
> >>>Satoshi Nagayasu escribi�:
> >>>
> >>>>With this patch, walwriter process and each backend process
> >>>>would sum up dirty writes, and send it to the stat collector.
> >>>>So, the value could be saved in the stat file, and could be
> >>>>kept on restarting.
> >>>>
> >>>>The statistics could be retreive with using
> >>>>pg_stat_get_xlog_dirty_writes() function, and could be reset
> >>>>with calling pg_stat_reset_shared('walwriter').
> >>>>
> >>>>Now, I have one concern.
> >>>>
> >>>>The reset time could be captured in globalStats.stat_reset_timestamp,
> >>>>but this value is the same with the bgwriter one.
> >>>>
> >>>>So, once pg_stat_reset_shared('walwriter') is called,
> >>>>stats_reset column in pg_stat_bgwriter does represent
> >>>>the reset time for walwriter, not for bgwriter.
> >>>>
> >>>>How should we handle this?  Should we split this value?
> >>>>And should we have new system view for walwriter?
> >>>
> >>>I think the answer to the two last questions is yes.  It doesn't seem to
> >>>make sense, to me, to have a single reset timings for what are
> >>>effectively two separate things.
> >>>
> >>>Please submit an updated patch to next CF.  I'm marking this one
> >>>returned with feedback.  Thanks.
> >>>
> >>
> >>I attached the latest one, which splits the reset_time
> >>for bgwriter and walwriter, and provides new system view,
> >>called pg_stat_walwriter, to show the dirty write counter
> >>and the reset time.
> >
> >I've done a quick review of the v4 patch:
> 
> Thanks for the review, and sorry for my delayed response.
> 
> >1) applies fine on HEAD, compiles fine
> >
> >2) "make installcheck" fails because of a difference in the 'rules'
> >    test suite (there's a new view "pg_stat_walwriter" - see the
> >    attached patch for a fixed version or expected/rules.out)
> 
> Ah, I forgot about the regression test. I will fix it. Thanks.
> 
> >3) I do agree with Alvaro that using the same struct for two separate
> >    components (bgwriter and walwriter) seems a bit awkward. For example
> >    you need to have two separate stat_reset fields, the reset code
> >    becomes much more verbose (because you need to list individual
> >    fields) etc.
> >
> >    So I'd vote to either split this into two structures or keeping it
> >    as a single structure (although with two views on top of it).
> 
> Ok, I will split it into two structs, PgStat_BgWriterGlobalStats and
> PgStat_WalWriterGlobalStats, and will modify PgStat_GlobalStats to
> hold those two structs in the stat collector.
> 
> >4) Are there any other fields that might be interesting? Right now
> >    there's just "dirty_writes" but I guess there are other values. E.g.
> >    how much data was actually written etc.?
> 
> AFAIK, I think those numbers can be obtained by calling
> pg_current_xlog_insert_location() or pg_current_xlog_location(),
> but if we need it, I will add it.
> 
> Regards,


-- 
Álvaro Herrera                http://www.2ndQuadrant.com/
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