Bruce Momjian wrote:
> If we only prune on an update (or insert) why not just do prune every
> time?  I figure the prune/defrag has to be lighter than the
> update/insert itself.

Pruning is a quite costly operation. You need to check the visibility of
each tuple on the page, following tuple chains as you go, mark line
pointers as not used or redirected, and finally memmove all the tuples
to remove the gaps between them. And it needs to be WAL-logged.

  Heikki Linnakangas

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