> >> Each time the record is updated, a new version is created, thus 
> >> lengthening the "correct" version search each time row is accessed,

> >> until, of course, the next vacuum comes along and corrects the
> >> to point to the latest version of the record.
> >>
> >> Is that a fair explanation?
> >
> > No, it's not.
> >
> > 1.  The index points to all the versions, until they get vacuumed

> it points to the last "current" version as updated by vacuum, or the
first version 
> of the row.

no, the index has one entry for each version of the row.
This is why updating only non-indexed columns is relatively expensive
in pg.


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