Re: OID/XID allocation (was Re: is PG able to handle a >500 GB Database?)

> Bruce Momjian <pgman@candle.pha.pa.us> writes:
> > What about pre-fetching of OID's.  Does that still happen for every
> > backend?
>
> Only ones that actually allocate some OIDs, I think.
>
> > What about XID's?
>
> XIDs are wasted on a postmaster restart, but not per-backend, because
> they are cached in shared memory instead of locally.  I've been thinking
> about changing the code so that OIDs are allocated in the same fashion.
> That would mean an extra spinlock grab per OID allocation, but so what?
> We grab several spinlocks per row creation already.  And we could
> increase the number of OIDs allocated per pg_variable file update,
> which would save some time.
>
> Haven't got round to it yet though, and I'm not sure but what Vadim
> might be planning to throw out all that code anyway ...

Added to TODO:

  * Move OID retrieval into shared memory to prevent lose of unused oids

Also, currently the oid can _not_ be used to determine the order rows
were inserted because one backend can grab its block of 50 and another
backend can start and insert a row first.

If we could change this with litle risk, it would be nice to have in
7.1, but I am sure someone will object.  :-)

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