Re: Help me recovering data

From: pgsql(at)mohawksoft(dot)com
To: "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: "Kouber Saparev" <postgresql(at)saparev(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Help me recovering data
Date: 2005-02-14 17:59:49
Message-ID: 16506.24.91.171.78.1108403989.squirrel@mail.mohawksoft.com
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It must be possible to create a tool based on the PostgreSQL sources that
can read all the tuples in a database and dump them to a file stream. All
the data remains in the file until overwritten with data after a vacuum.
It *should* be doable.

If there data in the table is worth anything, then it would be worth
extracting.

It would, of course, be a tool of last resort.

> "Kouber Saparev" <postgresql(at)saparev(dot)com> writes:
>> After asking the guys in the #postgresql(at)irc(dot)freenode(dot)net channel they
>> told
>> me that the reason is the "Transaction ID wraparound", because I have
>> never
>> ran VACUUM on the whole database.
>
>> So they proposed to ask here for help. I have stopped the server, but
>> what
>> could I do in order to save the data if it's possible at all?
>
> I think you're pretty well screwed as far as getting it *all* back goes,
> but you could use pg_resetxlog to back up the NextXID counter enough to
> make your tables and databases reappear (and thereby lose the effects of
> however many recent transactions you back up over).
>
> Once you've found a NextXID setting you like, I'd suggest an immediate
> pg_dumpall/initdb/reload to make sure you have a consistent set of data.
> Don't VACUUM, or indeed modify the DB at all, until you have gotten a
> satisfactory dump.
>
> Then put in a cron job to do periodic vacuuming ;-)
>
> regards, tom lane
>
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