Re: FSM versus GIN pending list bloat

On 4 August 2015 at 06:03, Jeff Janes <jeff(dot)janes(at)gmail(dot)com> wrote:

> The attached proof of concept patch greatly improves the bloat for both
> the insert and the update cases. You need to turn on both features: adding
> the pages to fsm, and vacuuming the fsm, to get the benefit (so JJ_GIN=3).
> The first of those two things could probably be adopted for real, but the
> second probably is not acceptable. What is the right way to do this?
> Could a variant of RecordFreeIndexPage bubble the free space up the map
> immediately rather than waiting for a vacuum? It would only have to move
> up until it found a page with freespace already recorded in it, which the
> vast majority of the time would mean observing up one level and then not
> writing to it, assuming the pending list pages remain well clustered.
>

You make a good case for action here since insert only tables with GIN
indexes on text are a common use case for GIN.

Why would vacuuming the FSM be unacceptable? With a
large gin_pending_list_limit it makes sense.

If it is unacceptable, perhaps we can avoid calling it every time, or
simply have FreeSpaceMapVacuum() terminate more quickly on some kind of
80/20 heuristic for this case.

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