Restore contsel/contjoinsel for containment & key-existence operators (#2356)

[crprashant]

Restore contsel/contjoinsel for containment & key-existence operators

Closes #2356.

Why

The containment (@>, <@, @>>, <<@) and key-existence (?, ?|, ?&) operators on agtype are bound to matchingsel / matchingjoinsel. matchingsel is intended for pattern operators (LIKE/regex) — during planning it invokes the operator's underlying function (agtype_contains) once per pg_statistic MCV entry. With realistic statistics targets that produces a planner-time regression that dominates simple OLTP-style point queries.

PostgreSQL core binds jsonb's analogous operators (@>, <@, ? on jsonb) to contsel / contjoinsel for exactly this reason. This PR restores that precedent for agtype.

What

• sql/agtype_operators.sql, sql/agtype_exists.sql: 10 operators flipped to contsel / contjoinsel.
• age--1.7.0--y.y.y.sql: appended ALTER OPERATOR ... SET (RESTRICT, JOIN) for all 10 operators so existing installs flip on ALTER EXTENSION age UPDATE.
• regress/sql/containment_selectivity.sql: new test that pins the bindings via pg_operator, plus a no-leaked-matchingsel aggregate guard and functional smoke for all 10 operators.
• regress/expected/cypher_match.out, regress/expected/cypher_vle.out: refresh expected — test_enable_containment now picks Nested Loop + Index Only Scans over Seq Scan/Hash Join (a direct, better plan), and two MATCH p=... and show_list_use_vle queries flip row order (they have no ORDER BY; result set unchanged).
• Makefile: register the new test in REGRESS.

Validation

Regression suite

36/37 pass with EXTRA_TESTS="pgvector fuzzystrmatch pg_trgm". Only age_upgrade fails — pre-existing on master at 774e781b (verified by git stash && installcheck baseline of 32/33 with the same age_upgrade failure).

Reporter's exact methodology — reproduced

Reporter's three scripts (generate_graph.sql, setup_func_for_workload.sql, workload_select.sql) used unchanged. Run on PG18 with default_statistics_target = 1000 to populate MCV lists, matching the reporter's analyzed-graph conditions:

Metric	matchingsel	contsel	Delta
EXPLAIN planning time	1.42 ms	0.97 ms	−32%
EXPLAIN execution time	0.34 ms	0.31 ms	~0%
pgbench TPS (8 clients × 30s)	5247	7378	+40.6%

The −32% planning-time delta lines up with the reporter's "~30% of execution time spent in agtype_contains during planning" observation; the +40.6% TPS gain matches the "severe TPS drop in OLTP-style workloads" they reported.

Upgrade path

Validated end-to-end during the benchmark: operator bindings were flipped from matchingsel → contsel via the same ALTER OPERATOR statements the upgrade SQL ships, while operators remained functional throughout.

pg_operator snapshots

-- Before (matchingsel binding shipped on master)
 oprname |  lhs   |  rhs   |  restrict_fn |    join_fn
---------+--------+--------+--------------+------------------
 <<@     | agtype | agtype | matchingsel  | matchingjoinsel
 <@      | agtype | agtype | matchingsel  | matchingjoinsel
 @>      | agtype | agtype | matchingsel  | matchingjoinsel
 @>>     | agtype | agtype | matchingsel  | matchingjoinsel
 ?       | agtype | agtype | matchingsel  | matchingjoinsel
 ?       | agtype | text   | matchingsel  | matchingjoinsel
 ?&      | agtype | agtype | matchingsel  | matchingjoinsel
 ?&      | agtype | text[] | matchingsel  | matchingjoinsel
 ?|      | agtype | agtype | matchingsel  | matchingjoinsel
 ?|      | agtype | text[] | matchingsel  | matchingjoinsel

-- After (this PR)
 oprname |  lhs   |  rhs   | restrict_fn |   join_fn
---------+--------+--------+-------------+-------------
 <<@     | agtype | agtype | contsel     | contjoinsel
 <@      | agtype | agtype | contsel     | contjoinsel
 @>      | agtype | agtype | contsel     | contjoinsel
 @>>     | agtype | agtype | contsel     | contjoinsel
 ?       | agtype | agtype | contsel     | contjoinsel
 ?       | agtype | text   | contsel     | contjoinsel
 ?&      | agtype | agtype | contsel     | contjoinsel
 ?&      | agtype | text[] | contsel     | contjoinsel
 ?|      | agtype | agtype | contsel     | contjoinsel
 ?|      | agtype | text[] | contsel     | contjoinsel

Driver workflows

Intentionally not run: this PR only adjusts pg_operator selectivity metadata. There is no C code, type, or wire-protocol change that python / go / node / JDBC drivers could observe.

Notes for reviewers

• matchingsel does provide better estimates when good statistics exist on heavily-analyzed agtype columns. PostgreSQL core accepts the same trade-off for jsonb. A future improvement (out of scope here) would be a custom agtype_contains_selectivity mirroring jsonb_sel; happy to file as a follow-up if there's interest.
• The containment_selectivity regression test is intentionally minimal so the diff is loud and precise if anyone re-introduces matchingsel here. The aggregate guard catches future operator additions that forget the right helper.

[crprashant]

Self-review caught a bug in the smoke test: SELECT ...::agtype ? 'a' was being parsed as the (agtype, agtype) overload (so 'a' was treated as an agtype literal — invalid syntax), producing an ERROR rather than verifying the (agtype, text) binding works. Added an explicit ::text cast on the right-hand side and regenerated the expected output.

Force-pushed amend 50beb10. Full installcheck still 36/37 (only pre-existing age_upgrade fails on master too).