Re: Adding skip scan (including MDAM style range skip scan) to nbtree - Mailing list pgsql-hackers

On Fri, May 9, 2025 at 9:33 AM Peter Geoghegan <pg@bowt.ie> wrote:
> Can you try it again, with prepared statements? Alternatively, you
> could selectively revert the changes that commit 92fe23d93aa made to
> utils/adt/selfuncs.c, and then retest.

Oh, wait, you already did try it with prepared statements.

I'm rather puzzled as to why this happens, then. I expect that nbtree
preprocessing will be able to use its usual single index column/index
key fast path here -- the "We can short-circuit most of the work if
there's just one key" path in _bt_preprocess_keys (and I expect that
_bt_num_array_keys() quickly determines that no skip arrays should be
added, preventing array preprocessing from ever really starting).

As far as I'm aware, none of the skip scan commits introduced new
palloc() overhead that would affect simple index scans like this. In
general that should only happen with index scans of a multicolumn
index that has at least one prefix column with no "=" condition. Most
individual index scans (including index scans that just use
inequalities) don't look like that.


--
Peter Geoghegan