Re: [ADMIN] Re: [SQL] Data recovery

> > If you only have the data/base subdirectory, you will need to work
> > harder; you'll have to regenerate the top-level files.  I think if you
> > get pg_shadow and pg_database right you will be OK.  First, install and
> > initdb to get a basic set of files.  You will need to recall the old set
> > of users (including their userIDs) in order to reconstruct pg_shadow.
> > After you've done the createusers, issue a createdb for each old
> > database (subdirectory of base/) so that they have entries in
> > pg_database.  Then, shut down the postmaster, blow away the contents of
> > the base/ subdirectory and restore it from tape, and restart.  I think
> > it'll work...
> >
> > In any case it's critical to install the same Postgres version you
> > were using.
>
>     NO  -  this  cannot  work.  He  surely  needs the entire data
>     directory because the information in the heap's relies on the
>     bits   in  data/pg_log.   And  that  info  (which  XID's  are
>     committed and which not) cannot  be  reconstructed  from  the
>     files - no chance.

Very, very hard, but not impossible.  If you update a row, and do a
select on that row, the select updates the transaction status so the
next select doesn't need to look at the pg_log table.  What this means
is that pg_log could probably be reconstructed from existing data, with
just 'unselected' changes not appearing properly.

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