Re: Subject: bool / vacuum full bug followup part 2

Tom Lane wrote:
> Scott Marlowe <scott(dot)marlowe(at)ihs(dot)com> writes:
> > And reclaimed the space. Is that the official way, short of dropping and
> > recreating an index to reclaim its space? Is there a plan to make vacuum
> > reclaim unused space in indexes?
>
> Yes, and yes, but don't hold your breath on the latter part --- that
> TODO item has been around for awhile. And it's gotten harder now that
> we have lazy VACUUM; that means we need to be able to condense indexes
> concurrently with other index operations.

Can you remind me why it is so hard to fix this. I do not expect lazy
vacuum to handle index shrinking, but it should be possible with full
vacuum.

> AFAIK there's not a big problem with index growth if the range of index
> keys remains reasonably static. The problem comes in if you have a
> range of values that keeps growing (eg, you are indexing a SERIAL or
> timestamp column). The right end of the btree keeps growing, but
> there's no mechanism to collapse out no-longer-used space at the left
> end.

I must say I am embarrased by our failure to shrink all indexes. I
haven't said this before because no one has complained.

I am sure lots of people are affected by this, but few realize it
because few analyze did space.

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