Re: vacuum, performance, and MVCC

Alvaro Herrera wrote:
> Jan Wieck wrote:
> > On 6/25/2006 10:12 PM, Bruce Momjian wrote:
> > >When you are using the update chaining, you can't mark that index row as
> > >dead because it actually points to more than one row on the page, some
> > >are non-visible, some are visible.
> > 
> > Back up the truck ... you mean in the current code base we have heap 
> > tuples that are visible in index scans because of heap tuple chaining 
> > but without index tuples pointing directly at them?
> 
> I don't know where this idea came from, but it's not true.  All heap
> tuples, dead or otherwise, have index entries.  Unless the idea is to
> extend update chaining to mean something different from the current
> meaning.

It does mean something different.  Single-Index-Tuple Chain (CITC) is a
special type of update chaining where the updates are all on the same
row, and a single index entry points to the entire chain.

--  Bruce Momjian   bruce@momjian.us EnterpriseDB    http://www.enterprisedb.com
 + If your life is a hard drive, Christ can be your backup. +