Re: pg_rawdump

On Tue, Oct 19, 2010 at 1:12 PM, Stephen R. van den Berg <srb@cuci.nl> wrote:
> In order to simplify recovery at this point (enormously), it would
> have been very helpful (at almost negligible cost), to have the name
> of the table, the name of the columns, and the types of the
> columns available.
>
> Why don't we insert that data into the first page of a regular table
> file after in the special data area?
>
> I'd be willing to create a patch for that (should be pretty easy),
> if nobody considers it to be a bad idea.

There isn't necessarily one value for these attributes.  You can
rename columns and that rename may succeed and commit or fail and
rollback. You can drop or add columns and some rows will have or not
have the added columns at all. You could even add a column, insert
some rows, then abort -- all in a transaction. So some (aborted) rows
will have extra columns that aren't even present in the current table
definition.

All this isn't to say the idea you're presenting is impossible or a
bad idea. If this meta information was only a hint for forensic
purposes and you take into account these caveats it might still be
useful. But I'm not sure how useful. I mean, you can't really decipher
everything properly without the data in the catalog -- and you have to
premise this on the idea that you've lost everything in the catalog
but not the data in other tables. Which seems like a narrow use case.

-- 
greg