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

Added to TODO:

* Expire published xmin for read-only and idle transactions
 http://archives.postgresql.org/pgsql-hackers/2007-09/msg00343.php


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Tom Lane wrote:
> 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
> 
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