Re: BUG #19701: GIN trigram index loses rows at similarity_threshold 0

Hi Palak,

Thanks for the review and for the row-set comparison.

On Fri, 25 Sept 2026, Palak Chaturvedi wrote:
> * Insert rows after creating the GIN index, then test an empty
> query at threshold zero before and after pending-list cleanup.
>
> * Include strict-word similarity (<<%) at zero, with stored empty
> strings and NULLs.

Both are in v2, attached. The new test uses a small table holding
two words, two empty strings and a NULL, inserted after the GIN index
is created. It runs % and <<%, with an empty and a non-empty query,
before and after gin_clean_pending_list(). It then rebuilds the index
as GiST and repeats the <<% queries. I added 1000 rows before the
GiST build: with only five rows the index is a single leaf page, and
leaf pages were already correct.

Without the C changes, each of the eight GIN queries returns 0 or 1
row instead of 4, both before and after the cleanup, and the empty
<<% query on GiST returns 0 instead of 1004. With them, pg_trgm's
tests pass. I checked this on master (45da2c1d756) and on
REL_14_STABLE, where v2 also applies cleanly.

Regards,
Manu