From: | Andres Freund <andres(at)2ndquadrant(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: slow startup due to LWLockAssign() spinlock |
Date: | 2014-02-03 23:58:49 |
Message-ID: | 20140203235849.GB12016@awork2.anarazel.de |
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Lists: | pgsql-hackers |
On 2014-02-03 11:22:45 -0500, Tom Lane wrote:
> Andres Freund <andres(at)2ndquadrant(dot)com> writes:
> > On larger, multi-socket, machines, startup takes a fair bit of time. As
> > I was profiling anyway I looked into it and noticed that just about all
> > of it is spent in LWLockAssign() called by InitBufferPool(). Starting
> > with shared_buffers=48GB on the server Nate Boley provided, takes about
> > 12 seconds. Nearly all of it spent taking the ShmemLock spinlock.
> > Simply modifying LWLockAssign() to not take the spinlock when
> > !IsUnderPostmaster speeds it up to 2 seconds. While certainly not making
> > LWLockAssign() prettier it seems enough of a speedup to be worthwile
> > nonetheless.
>
> Hm. This patch only works if the postmaster itself never assigns any
> LWLocks except during startup. That's *probably* all right, but it
> seems a bit scary. Is there any cheap way to make the logic actually
> be what your comment claims, namely "Interlocking is not necessary during
> postmaster startup"? I guess we could invent a ShmemInitInProgress global
> flag ...
So, here's a flag implementing things with that flag. I kept your name,
as it's more in line with ipci.c's naming, but it looks kinda odd
besides proc_exit_inprogress.
Greetings,
Andres Freund
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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faster-init-buffer-pool-v2.diff | text/x-diff | 3.0 KB |
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