Re: buffer assertion tripping under repeat pgbench load

On 12/26/12 7:23 PM, Greg Stark wrote:
> It's also possible it's a bad cpu, not bad memory. If it affects
> decrement or increment in particular it's possible that the pattern of
> usage on LocalRefCount is particularly prone to triggering it.

This looks to be the winning answer. It turns out that under extended
multi-hour loads at high concurrency, something related to CPU
overheating was occasionally flipping a bit. One round of compressed
air for all the fans/vents, a little tweaking of the fan controls, and
now the system goes >24 hours with no problems.

Sorry about all the noise over this. I do think the improved warning
messages that came out of the diagnosis ideas are useful. The reworked
code must slows down the checking a few cycles, but if you care about
performance these assertions are tacked onto the biggest pig around.

I added the patch to the January CF as "Improve buffer refcount leak
warning messages". The sample I showed with the patch submission was a
simulated one. Here's the output from the last crash before resolving
the issue, where the assertion really triggered:

WARNING: buffer refcount leak: [170583] (rel=base/16384/16578,
blockNum=302295, flags=0x106, refcount=0 1073741824)
WARNING: buffers with non-zero refcount is 1
TRAP: FailedAssertion("!(RefCountErrors == 0)", File: "bufmgr.c", Line:
1712)

--
Greg Smith 2ndQuadrant US greg(at)2ndQuadrant(dot)com Baltimore, MD
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