Re: Low hanging fruit in lazy-XID-assignment patch?

Alvaro Herrera <alvherre@commandprompt.com> writes:
> As a fallout of this work that I haven't seen made explicit, a session
> opening a transaction and then sitting around doing nothing will not
> cause as many problems as it used to -- for example it won't cause
> VACUUM to be unable to clean up dead rows.  Is this correct?

Yeah, if you just issue BEGIN and then sit, you won't have acquired
either an xid or an xmin, so you don't create a VACUUM problem anymore.

If you issue BEGIN, then SELECT, then sit, you'll be publishing an xmin
but not an xid, so at that point you become a problem for VACUUM.
However, internally you don't have any live snapshots (if you're in READ
COMMITTED mode), so eventually we could have you stop publishing an xmin
too.  That's something for 8.4 though.
        regards, tom lane