Re: Hot standby and removing VACUUM FULL

On Wed, 2009-11-25 at 03:12 +0000, Greg Stark wrote:
> On Wed, Nov 25, 2009 at 2:10 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> > As long as there's not anything the master actually does differently
> > then I can't see where there'd be any performance testing to do.  What's
> > bothering me about this is that it seems likely that we'll find places
> > where the master has to do things differently.  I'd rather we made the
> > status visible; if we get through a release cycle without needing to
> > check it, we can always take the function out again.  But if we don't,
> > and then find out midway through the 8.5 release cycle that we need to
> > be able to check it, things could be a bit sticky.
> 
> Well the only thing that's been discussed is having vacuum require a
> minimum age before considering a transaction visible to all to reduce
> the chance of conflicts on cleanup records. But that would require an
> actual tunable, not just a flag. And it's something that could
> conceivably be desirable even if you're not running a HS setup (if
> someone ever reimplements time travel for example).

I've added "vacuum_delay_cleanup_age = N", default 0 to implement this.
New name please.

This alters the return value of GetOldestXmin() and the setting of
RecentGlobalXmin by the value requested.

I've made this a SIGHUP, since it only has value if it affects all
users.

-- Simon Riggs           www.2ndQuadrant.com