Re: could not access status of transaction

Hi Tom,

On Mar 25, 2009, at 9:02 PM, Tom Lane wrote:

> Tom Duffey <tduffey(at)techbydesign(dot)com> writes:
>> One of our databases suffered a problem yesterday during a normal
>> update, something we have been doing for years. Near the end of the
>> process a foreign key constraint is rebuilt on a table containing
>> several hundred million rows. Rebuilding the constraint failed with
>> the following message:
>
>> ERROR: could not access status of transaction 4294918145
>> DETAIL: Could not open file "pg_clog/0FFF": No such file or
>> directory.
>
> This looks like a garden-variety data corruption problem to me.
> Trashed rows tend to yield this type of error because the "xmin"
> transaction ID is the first field that the server can check with
> any amount of finesse. 4294918145 is FFFF4001 in hex, saith my
> calculator, so it looks like a bunch of bits went to ones --- or
> perhaps more likely, the row offset in the page header got clobbered
> and we're looking at some bytes that never were a transaction ID
> at all.
>
> So I'd try looking around for flaky RAM, failing disks, loose cables,
> that sort of thing ...

Are you aware of any issues like this related to VMWare ESX? Our
PostgreSQL server is running in such an environment and I asked the
guys to review your email and they thought maybe this type of
corruption could happen when the virtual machine was moved from one
physical server to another, which we have done once or twice in the
past few months.

Tom

--
Tom Duffey <tduffey(at)techbydesign(dot)com>
Technology by Design :: http://techbydesign.com/
p: 414.431.0800