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Re: could not read block 77 of relation 1663/16385/388818775

From: Alexandra Nitzschke <an(at)clickware(dot)de>
To: pgsql-bugs(at)postgresql(dot)org
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Craig Ringer <craig(at)postnewspapers(dot)com(dot)au>
Subject: Re: could not read block 77 of relation 1663/16385/388818775
Date: 2008-11-24 16:55:14
Message-ID: 492ADC72.3080109@clickware.de (view raw or flat)
Thread:
Lists: pgsql-bugs
Hi,

first of all I would like to thank you for all your efforts.

 > We really need a test case.

unfortunately this kind of bugs tend to be non-reproducable. I assume that there is a race condition which is only hit 
in rare cases, under heavy load and when mars and venus are exactly aligned... ;-)

I do not think it is possible to construct a test case that reliably reproduces the bug.

However, we would be glad to incorporate any patches, additional logging code etc. in our installation of postgres that 
might help you to track the bug. Since we always build postgres on the production machine this would not be any problem.

Unfortunately we handle very sensitive data in our databases, so we cannot give you direct access to our machines. As a 
  last resort I would propose the following (provided that our customer agrees):

We set up another machine and feed it with obfuscated data, putting it under the same load as our production machine. We 
could then give you root access to that machine and you could do whatever patching, monitoring, testing etc. might be 
helpful to track the problem. Do you think this might help?

BTW... how about a block checksum that is checked just before writing a block and just after reading it? I know this 
would degrade performance, but I think we can afford that. Would it be possible to incorporate such code without having 
to do too much patching?

Thanks in advance

Alexandra Nitzschke
Thomas Goerner


Tom Lane schrieb:
> Alexandra Nitzschke <an(at)clickware(dot)de> writes:
>> Yes, its a btree.
> 
> Well, the btree code is sufficiently well tested/debugged that I think
> there's zero chance of finding such a bug in it just on the suspicion
> that there might be one there.  We really need a test case.
> 
> 			regards, tom lane
> 
> 

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