Tatsuo Ishii wrote:

> Just for curiousity, why FSM gathers info for indexes? I thought FSM
> is only good for tables.

It's part of the implementation of the page-recycling algorithm for
btrees Tom did for 7.4. When a btree page is empty after a vacuum, it's
entered in the free space map. When a page is split, the new page is
taken from the FSM (or the relation is extended if there isn't any.)

That's why the bytes-free number is zero: when a btree page makes it
into the FSM, we are sure it's completely empty.

--
Alvaro Herrera http://www.CommandPrompt.com/
PostgreSQL Replication, Consulting, Custom Development, 24x7 support

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