Re: vacuum, performance, and MVCC

Hannu Krosing wrote:
> > > Maybe we could start from reusing the index tuples which point to
> > > invisible tuples ? The index is not MVCC anyway, so maybe it is easier
> > > to do in-place replacement there ?
> > >
> > > This probably has the same obstacles which have prevented us from
> > > removing those in the first place (removing instead of marking as
> > > invisible). Does it cause some locking issues ? Or does it go against
> > > some other constraints of our index lookups ?
> > >
> > > I think that just setting the invisible bit in an index leaf node causes
> > > nearly as much disk io as removing the node.
> > >
> > > If we could delete/reuse old index tuples, it would solve a sizable
> > > chunk of index-growth problem, especially for cases where referenced key
> > > value does not change.
> >
> > I think heap _and_ index reuse is the only useful direction. Index or
> > heap reuse alone seems too marginal for the added complexity.
>
> Sure, but index reuse seems a lot easier, as there is nothing additional
> to remember or clean out when doing it.

Yes, seems so. TODO added:

* Reuse index tuples that point to heap tuples that are not visible to
anyone?

> When reusing a heap tuple you have to clean out all index entries
> pointing to it.

Well, not for UPDATE for no key changes on the same page, if we do that.

--
Bruce Momjian bruce(at)momjian(dot)us
EnterpriseDB http://www.enterprisedb.com

+ If your life is a hard drive, Christ can be your backup. +