-- pg_tre 4.0.0 -> 4.0.1 upgrade.
--
-- No catalog changes.  4.0.1 fixes a storage leak: a pending-list merge
-- rebuilt the upper tree and abandoned every page of the old one, so an
-- index under sustained delete+reinsert churn grew without bound (the
-- long-standing stress-scenario-G finding).  Storage-layer only; `diff
-- sql/pg_tre--4.0.0.sql sql/pg_tre--4.0.1.sql` differs only in the header
-- comment.
--
-- No on-disk format change and NO REINDEX required.  Pages leaked by
-- earlier versions are not retroactively reclaimed -- nothing recorded
-- which blocks they were -- so the next merge stops adding to the pile and
-- a REINDEX recovers the historical waste if you want the space back.
--
-- Also adds DEBUG1 instrumentation to the plain Index Scan (amgettuple)
-- path, which previously had none.  If you are chasing a scan that returns
-- unexpected row counts:
--
--   SET client_min_messages = debug1;
--   SET enable_seqscan = off; SET enable_bitmapscan = off;   -- amgettuple
--   SELECT count(*) FROM your_table WHERE col ~* '^Pattern';
--
-- reports whether extraction went always_true, the candidate cardinality,
-- and how many TIDs were emitted -- which separates "no candidates" from
-- "empty heap stream" from "recheck filtered everything".