Re: Hot Standby and VACUUM FULL

On Sun, 2010-01-31 at 15:14 -0500, Tom Lane wrote:
> Simon Riggs <simon(at)2ndQuadrant(dot)com> writes:
> > On Sun, 2010-01-31 at 14:35 -0500, Tom Lane wrote:
> >> Anyway, it's still not apparent to me exactly what the connection is
> >> between VACUUM FULL and Hot Standby. I remember that we said HS didn't
> >> work with VACUUM FULL (INPLACE) but I don't recall why that is, and the
>
> [ sorry, I meant not-INPLACE ]
>
> >> links on the open-items pages are not leading me to any useful
> >> discussion.
>
> > Very little really; not enough to force the sort of changes that I am
> > now seeing will be required in the way catalogs and caches operate.
> > There was some difficulty around the fact that VFI issues two commits
> > for the same transaction, but that is now correctly handled in the code
> > after discussion.
>
> If the only benefit of getting rid of VACUUM FULL were simplifying
> Hot Standby, I'd agree with you. But there are numerous other benefits.
> The double-commit hack you mention is something we need to get rid of
> for general system stability (because of the risk of PANIC if the vacuum
> fails after the first commit). Getting rid of REINDEX-in-place on
> shared catalog indexes is another thing that's really safety critical.
> Removing V-F related hacks in other places would just be a bonus.
>
> It's something we need to do, so if Hot Standby is forcing our hands,
> then let's just do it.

That's the point: Hot Standby is *not* forcing our hand to do this.

Doing this will not simplify Hot Standby in any significant way. The
code to support VFI with Hot Standby is, after technical review, much,
much simpler than the code to remove VFI.

I'll do a little work towards step (1) just so we can take a more
informed view once you've had a better look at just what (2) involves. I
had already written the code for the Sept release of HS.

--
Simon Riggs www.2ndQuadrant.com