From: Noah Misch <noah@leadboat.com>
To: cygwin@cygwin.com
Subject: Re: cygserver - Postgres Multiple connection Load Testing - Inifinte Loop
Date: Tue, 28 Mar 2017 05:48:00 -0000 [thread overview]
Message-ID: <20170328052652.GA2351961@tornado.leadboat.com> (raw)
In-Reply-To: <20170324171101.GI29995@calimero.vinschen.de>
On Fri, Mar 24, 2017 at 06:11:01PM +0100, Corinna Vinschen wrote:
> - cygserver is using a defined number of threads in a thread pool for
> application requests. Every request is added to a request submission
> queue and handled by the next free thread in the pool.
>
> The default number of threads in the pool is 10. Each wait for a
> semaphore is blocking one thread. If more than the number of threads
> in the pool are supposed to wait on a semaphore the pool starves.
Interesting. I can confirm that, without updating software, "cygserver -r 40"
fixes both my self-contained test and my PostgreSQL test case. Folks can use
that workaround in released-version installations.
> So what I did now is to allow cygserver to raise the number of worker
> threads on demand. That is, if a request is in the queue and all
> worker threads are busy, just create a new one.
>
> There's no way yet to drop threads again, but this should be a minor
> problem in scenarions which really have a lot of contention.
Agreed. This is nicer.
> I pushed a patchset now, and uploaded new developer snapshots for
> testing to https://cygwin.com/snapshots/
> Please give it a try
Self-contained test case results look good:
cygwin-20170321.tar.xz "cygserver -r40": ok
cygwin-20170324.tar.xz "cygserver -r40": ok
cygwin-20170321.tar.xz "cygserver -r10": freezes (expected)
cygwin-20170324.tar.xz "cygserver -r10": ok; cygserver output concludes with
"cygserver: All threads busy, added one (now 21)".
I then tried my PostgreSQL test case ("pgbench -i -s 50" once to setup, then
"pgbench -S -j2 -c16 -T900 -P5" to test):
cygwin-20170321.tar.xz "cygserver -r40": ok for >3600s
cygwin-20170324.tar.xz "cygserver -r40": limited freeze in <1000s; no
cygserver output
cygwin-20170321.tar.xz "cygserver -r10": classic freeze in <1000s (expected)
cygwin-20170324.tar.xz "cygserver -r10": limited freeze in <1000s; no
cygserver output for most of the run, then output concluding with
"cygserver: All threads busy, added one (now 15)" just before the freeze
I call the cygwin-20170324 freezes "limited" because the symptoms differ from
the classic freeze I described upthread. "strace /bin/true" and "cat
/proc/sysvipc/sem" do not hang, but every PostgreSQL backend process is stuck
waiting on a synchronization primitive.
I can distill another self-contained test case for the limited freeze seen in
cygwin-20170324, but that make take awhile. I'm sending this early report so
you're aware of the possible regression in cygwin-20170324.
Thanks,
nm
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next prev parent reply other threads:[~2017-03-28 5:31 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <200408030333.i733XEXn023894@mx3.redhat.com>
2004-08-03 10:06 ` Corinna Vinschen
2004-08-03 20:45 ` Saravanan Bellan
2004-08-03 20:54 ` Christopher Faylor
2004-08-03 21:10 ` Saravanan Bellan
2017-03-21 2:56 ` Noah Misch
2017-03-21 7:29 ` Marco Atzeri
2017-03-24 17:52 ` Corinna Vinschen
2017-03-25 10:55 ` Marco Atzeri
2017-03-25 12:02 ` Corinna Vinschen
2017-03-25 12:31 ` Marco Atzeri
2017-03-28 5:48 ` Noah Misch [this message]
2017-04-02 2:36 ` Noah Misch
2017-05-07 3:35 ` Noah Misch
2017-05-07 4:01 ` Larry Hall (Cygwin)
2017-06-14 23:32 ` Marco Atzeri
2017-06-20 11:11 ` Corinna Vinschen
2017-06-20 17:29 ` Marco Atzeri
2017-06-21 7:58 ` Corinna Vinschen
2004-08-03 3:33 sarbx-cygwin6344
[not found] <200407302132.i6ULWwXn016838@mx3.redhat.com>
2004-08-02 9:45 ` Corinna Vinschen
-- strict thread matches above, loose matches on Subject: below --
2004-07-30 22:09 sarbx-cygwin6344
[not found] <200407290319.i6T3JCXn018245@mx3.redhat.com>
2004-07-30 13:43 ` Corinna Vinschen
2004-07-29 10:35 sarbx-cygwin6344
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