Re: vacuum, performance, and MVCC

Martijn van Oosterhout wrote:
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> On Mon, Jun 26, 2006 at 07:17:31AM -0400, Bruce Momjian wrote:
> > Correct!  We use the same pointers used by normal UPDATEs, except we set
> > a bit on the old tuple indicating it is a single-index tuple, and we
> > don't create index entries for the new tuple.  Index scan routines will
> > need to be taught about the new chains, but because only one tuple in
> > the chain is visible to a single backend, the callers should not need to
> > be modified.
> 
> I suppose we would also change the index_getmulti() function to return
> a set of ctids plus flags so the caller knows to follow the chains,
> right? And for bitmap index scans you would only remember the page in
> the case of such a tuple, since you can't be sure the exact ctid you've
> got is the one you want.
> 
> Seems doable.

Yes, it just is an issue of where you want to add the complexity ---
scan entire page when no free space, or only an UPDATE.

--  Bruce Momjian   bruce@momjian.us EnterpriseDB    http://www.enterprisedb.com
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