Re: Some thoughts about i/o priorities and throttling vacuum

On Fri, Oct 17, 2003 at 07:41:38PM +0530, Shridhar Daithankar wrote:
> Alvaro Herrera wrote:
>
> >On Fri, Oct 17, 2003 at 07:04:45PM +0530, Shridhar Daithankar wrote:

> >The database can suffer XID wraparound anyway if there's at least one
> >table without updates, because the autovacuum daemon will never vacuum
> >it (correct me if I'm wrong).
>
> If a table is never updated and hence not vacuumed at all, why would it be
> involved in a transaction that would have xid wrap around?

Because the tuples on it were involved in some insert operation at some
time (else the table would not have any tuples). So it _has_ to be
vacuumed, else you run the risk of losing the tuples when the wraparound
happens. (Sorry, I don't know how to explain this better.)

Maybe in this case it's best to do a VACUUM FREEZE; that'd ensure that
the table would never ever need a vacuum again until it suffers
an insert, delete or update. Perhaps the autovacuum daemon could detect
the case where a table has only very old tuples and freeze it.

--
Alvaro Herrera (<alvherre[a]dcc.uchile.cl>)
"El número de instalaciones de UNIX se ha elevado a 10,
y se espera que este número aumente" (UPM, 1972)