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

From: Gregory Stark <stark(at)enterprisedb(dot)com>
To: John R Pierce <pierce(at)hogranch(dot)com>
Cc: pgsql-bugs(at)postgresql(dot)org
Subject: Re: could not read block 77 of relation 1663/16385/388818775
Date: 2008-11-26 09:38:24
Message-ID: 87iqqarfn3.fsf@oxford.xeocode.com (view raw or flat)
Thread:
Lists: pgsql-bugs
John R Pierce <pierce(at)hogranch(dot)com> writes:

> Alexandra Nitzschke wrote:
>> 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?
>
> oracle has had an option for some time that uses read/only page protection for
> each page of the shared buffer area...   when oracle knows it wants to modify a
> page, it un-protects it via a system call.     this catches any wild writes
> into the shared buffer area as a memory protection fault.

The problem with both of these approaches is that most bugs occur when the
code *thinks* it's doing the right thing. A bug in the buffer management code
which returns the wrong buffer or a real wild pointer dereference. I don't
remember ever having either of those.

That said, the second option seems pretty trivial to implement. I think the
performance would be awful for a live database but for a read-only database it
might make more sense.

-- 
  Gregory Stark
  EnterpriseDB          http://www.enterprisedb.com
  Ask me about EnterpriseDB's Slony Replication support!

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Next:From: John R PierceDate: 2008-11-26 10:06:24
Subject: Re: could not read block 77 of relation 1663/16385/388818775
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Subject: BUG #4550: ecpg problem with copy command and hostvar

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