On 6/25/2006 12:27 PM, Bruce Momjian wrote:
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.
An update that results in all the same values of every indexed column of
a known deleted invisible tuple. This reused tuple can by definition not
be the one currently updated. So unless it is a table without a primary
key, this assumes that at least 3 versions of the same row exist within
the same block. How likely is that to happen?
Jan
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