[users at bb.net] Performance issues in 2.10

Tue Jan 12 21:13:50 UTC 2021

Thanks for the update.

Some random thoughts...

You should probably leave the profiler open until you get the performance
spike.
If you are inside the spike when starting, indeed, you won't be able to
start profiler, but if it is started before the spike it for sure will
detect exactly where the code is.
statistic profiling will use timer interrupts which will preempt anything
that is running, and make a call stack trace.

Waiting for repro, if, from the db log, you manage to get the info of what
kind of db data that is, maybe we can narrow down the usual suspects..

If there are lots of short selects like you said, usually, you would have a
back and forth from reactor thread to db thread, so it sounds weird.
What can be leading to your behavior is that whatever is halting the
processing, everything is queued up in between, and unqueued when it is
finished, which could lead to spike of db actions in the end of the event.

Regards
Pierre

Le mar. 12 janv. 2021 à 21:49, Yngve N. Pettersen <yngve at vivaldi.com> a
écrit :

> Hi again,
>
> A bit of an update.
>
> I have not been able to locate the issue using the profiler.
>
> It seems that when Buildbot gets into the problematic mode, then the
> profiler is not able to work at all. It only starts collecting after the
> locked mode is resolved.
>
> It does seem like the locked mode occurs when Buildbot is fetching a lot
> of data from the DB and then spends a lot of time processing that data,
> without yielding to other processing needs.
>
> Looking at the monitoring of the server, it also appears that buildbot is
> fetching a lot of data. During the most recent instance, the returned
> tuples count in the graph for the server indicates three minutes of, on
> average 25000 tuples returned, with spikes to 80K and 100K, per second.
>
> The number of open connections rose to 6 or 7, and the transaction count
> was 400-500 per second during the whole time (rolled back transactions,
> which I assume is just one or more selects).
>
> IMO this makes it look like, while requesting these data, Buildbot is
> *synchronously* querying the DB and processing the returned data, not
> yielding. It might also be that it is requesting data more data than it
> needs, and also requesting other data earlier than it is actually needed.
>
>
>
> On Tue, 12 Jan 2021 12:48:40 +0100, Yngve N. Pettersen <yngve at vivaldi.com>
>
> wrote:
>
> > Hi,
> >
> > IIRC the only real processing in our system that might be heavy is done
> > via logobserver.LineConsumerLogObserver in a class (now) derived from
> > ShellCommandNewStyle, so if that is the issue, and deferToThread is the
> > solution, then if it isn't already done, my suggestion would be to
> > implement that inside the code handling the log observers.
> >
> > I've tested the profiler a little, but haven't seen any samples within
> > our code so far, just inside buildbot, quite a lot of log DB actions,
> > also some TLS activity.
> >
> > The performance issue for those pages seems to be a bit flaky; at
> > present its not happening AFAICT
> >
> > On Tue, 12 Jan 2021 10:59:42 +0100, Pierre Tardy <tardyp at gmail.com>
> > wrote:
> >
> >> Hello,
> >>
> >> A lot of things happen between 2.7 and 2.10, although I don't see
> >> anything
> >> which could impact the performance that much. (maybe new reporter
> >> framework, but really not convinced)
> >> If you see that the db is underutilized this must be a classical reactor
> >> starvation.
> >> With asynchronous systems like buildbot, you shouldn't do any heavy
> >> computation in the main event loop thread, those must be done in a
> >> thread
> >> via deferToThread and co.
> >>
> >> Those are the common issues you can have with performance
> >> independantly from upgrade regressions:
> >>
> >> 1) Custom steps:
> >> A lot of time, we see people struggling with performance when they just
> >> have some custom step doing heavy computation that block the main thread
> >> constantly, preventing all the very quick tasks to run in //.
> >>
> >> 2) too much logs
> >>  In this case, there is not much to do beside reducing the log amount.
> >> This
> >> would be the time to switch to a multi-master setup, where you put 2
> >> masters for builds, and one master for web UI.
> >> You can put those in the same machine/VM, no problem, the only work is
> >> to
> >> have separate processes that each have several event queues. You can use
> >> docker-compose or kubernetes in order to more easily create such
> >> deployment. We don't have readily useable for that, but several people
> >> have
> >> done and documented it, for example
> >> https://github.com/pop/buildbot-on-kubernetes
> >>
> >>
> >> I have developed the buildbot profiler in order to quickly find those.
> >> You
> >> just have to install it as a plugin and start a profile whenever the
> >> buildbot feels slow.
> >> It is a statistical profiler, so it will not significantly change the
> >> actual performance so it is safe to run in production.
> >>
> >> https://pypi.org/project/buildbot-profiler/
> >>
> >>
> >> Regards,
> >> Pierre
> >>
> >>
> >> Le mar. 12 janv. 2021 à 01:29, Yngve N. Pettersen <yngve at vivaldi.com> a
> >> écrit :
> >>
> >>> Hello all,
> >>>
> >>> We have just upgraded our buildbot system from 2.7 to 2.10.
> >>>
> >>> However, I am noticing performance issues when loading these pages:
> >>>
> >>>   Builds->Builders
> >>>   Builds->Workers
> >>>   individual builds
> >>>
> >>> Loading these can take several minutes, although there are periods of
> >>> immediate responses.
> >>>
> >>> What I am seeing on the buildbot manager machine is that the Python3
> >>> process hits 90-100% for the entire period.
> >>>
> >>> The Python version is 3.6.9 running on Ubuntu 18.04
> >>>
> >>> As far as I can tell, the Postgresql database is mostly idle during
> >>> this
> >>> period. I did do a full vacuum a few hours ago, in case that was the
> >>> issue.
> >>>
> >>> There are about 40 builders, and 30 workers in the system, only about
> >>> 10-15 of these have a 10-20 builds for the past few days, although most
> >>> of
> >>> these have active histories of 3000 builds (which do make me wonder if
> >>> the
> >>> problem could be a lack of limiting the DB queries, at present I have
> >>> not
> >>> inspected the DB queries).
> >>>
> >>> The individual builds can have very large log files in the build steps,
> >>> in
> >>> many cases tens of thousands of lines (we _are_ talking about a
> >>> Chromium
> >>> based project).
> >>>
> >>> Our changes in the builders and workers JS code are minimal (we are
> >>> using
> >>> a custom build of www-base), just using different information for the
> >>> build labels (build version number), and grouping the builders, which
> >>> should not be causing any performance issues. (we have larger changes
> >>> in
> >>> the individual builder view, where we include Git commit messages,
> and
> >>> I
> >>> have so far not seen any performance issues there)
> >>>
> >>> BTW: The line plots for build time and successes on builders seems to
> >>> be
> >>> MIA. Not sure if that is an upstream issue, or due to something in our
> >>> www-base build.
> >>>
> >>> Do you have any suggestions for where to look for the cause of the
> >>> problem?
> >>>
> >>>
> >>> --
> >>> Sincerely,
> >>> Yngve N. Pettersen
> >>> Vivaldi Technologies AS
> >>> _______________________________________________
> >>> users mailing list
> >>> users at buildbot.net
> >>> https://lists.buildbot.net/mailman/listinfo/users
> >>>
> >
> >
>
>
> --
> Sincerely,
> Yngve N. Pettersen
> Vivaldi Technologies AS
>
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