Hannu Krosing <[EMAIL PROTECTED]> writes:
> and I can't see why btree stores them (as it seems to do judging by the 
> index file size) - at least it does not use it for searching for "IS
> NULL"

That's another thing that needs improvement ;-).  Seems to me it should
be able to do that.

The reason why btree *has* to be able to deal with null entries is to
cope with multi-column indexes; you don't want it refusing to index a
row at all just because some of the columns are null.  The others don't
currently handle multi-column indexes, so they're not really forced
to deal with that issue.

>From a purely semantic point of view I'm not sure why Oleg is worried
about being able to store nulls in a GiST index ... seems like leaving
them out is OK, modulo the occasional complaint from VACUUM's
insufficiently intelligent tuple-count comparison ...

                        regards, tom lane

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