Re: Duplicate primary keys/rows

I don't have a compiler on this machine. If somebody
can point me to a copy of pg_filedump for Windows (I
didn't see any using Google) I'd be happy to use it.
Or perhaps I could compile it under cygwin.

The hard drive is a Western Digital 200GB JD (SATA),
if that can be used to determine how badly it lies. ;)

Thanks,
CSN

--- Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> CSN <cool_screen_name90001(at)yahoo(dot)com> writes:
> > oid | ctid | xmin | cmin | xmax |
> cmax | id
> >
>
--------+-----------+---------+------+---------+------+-----
> > 125466 | (2672,11) | 1445346 | 0 | 1481020 |
> 0 | 985
> > 125466 | (2745,50) | 1481020 | 0 | 1682425 |
> 2 | 985
>
> Hmm. The fact that the dup rows have the same OID
> indicates pretty
> strongly that they are actually two versions of the
> same row, and
> not two independently inserted rows. Furthermore we
> can see that xact
> 1481020 deleted the first version and inserted the
> second (note I took
> the liberty of rearranging your output to make the
> rows appear in
> chronological order).
>
> So the index hasn't screwed up, exactly; the problem
> is that both rows
> appear as good at the same time. But why?
>
> It's really highly annoying that we can't see the
> contents of the
> infomasks for the rows. Would you be willing to
> grab a copy of
> pg_filedump and dump out these two data pages so we
> can see the
> complete tuple headers?
>
> (If you don't have a compiler then you'd need to
> find a precompiled
> copy of pg_filedump for Windows. I don't know if
> anyone's made one
> available.)
>
> Given that you say the machine has been crashing, my
> bet is that a crash
> caused the loss of pg_clog status for xid 1481020 at
> a time when
> 2745,50's xmin had been marked committed good, but
> 2672,11's xmax had
> not been similarly marked. We have sufficient
> defenses against this
> sort of thing *if the disk drive does not lie about
> write complete*.
> (Unfortunately the vast majority of el-cheapo PCs
> are configured to lie
> with abandon, which means that we can't guarantee
> data consistency
> across power failures on such hardware.) It'd be
> nice to get direct
> confirmation of that theory though.
>
> regards, tom lane
>

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