Re: Free space mapping (was Re: Multi-Versions and Vacuum)

On Fri, Jul 19, 2002 at 02:11:09PM -0400, Tom Lane wrote:

> However, if the FSM is vastly smaller than the number of
> actively-changing pages in your database, then that argument breaks down
> --- in particular, if the FSM can't even keep track of all the
> completely-empty pages in your database then you are going to suffer
> progressive leakage.

That's consistent with the reports people have made, because it was
always in the case of databases with extremely high turnover that it
turned up.  So at the very least, people who anticipate high turnover
on their systems should set the free space map higher (and maybe
vacuum more often -- AFAIK, though, no-one has yet documented the
performance penalty of non-blocking vacuum.  I guess it should be no
worse than any other client, but I'm not sure, and haven't tested
yet).

A

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