Re: linux bug and lost rows - Mailing list pgsql-general

Tom Lane wrote:
> Jaime Silvela <JSilvela@Bear.com> writes:
>
>> A long time ago I wrote to the list about a problem I was having with
>> COPY losing rows from an import file: the number of imported rows was
>> not equal to the number of rows in the file, and two consecutive imports
>> from the same file would get different row counts. Several people tried
>> to reproduce it unsuccessfully. Reference:
>> http://archives.postgresql.org/pgsql-general/2006-07/msg00925.php
>>
>
>
>> More recently, as I was practicing a database upgrade to 8.2.3, I
>> captured an "unexpected data beyond EOF" in the log, which led to
>> missing tables in the upgraded db. I opened a thread, and it turned out
>> someone had previously had the same problem, and it was due to the Linux
>> kernel version: 2.6.5-7.244
>> Reference: http://archives.postgresql.org/pgsql-general/2007-03/msg01543.php
>>
>
>
>> Now my server has been upgraded to 2.6.5-7.282, and I'm happy to report
>> that BOTH problems have disappeared. The first problem, that of lost
>> rows for COPY, tended to present itself for large import files, nearing
>> 1GB, but I was never able to get reproducible results. As I understand,
>> the Linux bug responsible for the "unexpected data beyond EOF" had to do
>> with faulty disk reads. Probably this was also affecting the COPY
>> command, only failing silently?
>>
>
> Your COPY problems were all on PG 8.1.x, right?  The "unexpected data
> beyond EOF" check was added in 8.2.0 specifically because we realized we
> were getting bit by a Linux kernel bug.  In 8.1, manifestations of that
> same bug would have just led to silent data loss.  The cases that we
> identified before all seemed to involve concurrent insertions by
> different backends, but I don't think anyone has hard proof that it
> couldn't happen for successive insertions by a single backend.  So yeah,
> it now seems highly likely that that bug explains the COPY problem.
>
> Out of sheer conservatism, I didn't backpatch the "unexpected data
> beyond EOF" check into pre-8.2 stable branches, but I wonder if we
> shouldn't do that now.
>
>             regards, tom lane
>
>
Right, the problems showed up on 8.1.3.

Thanks
Jaime


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