From b262ad440edecda0b1aba81d967ab560a83acb8a Mon Sep 17 00:00:00 2001 From: David Rowley Date: Tue, 23 Jan 2024 18:09:18 +1300 Subject: Add better handling of redundant IS [NOT] NULL quals Until now PostgreSQL has not been very smart about optimizing away IS NOT NULL base quals on columns defined as NOT NULL. The evaluation of these needless quals adds overhead. Ordinarily, anyone who came complaining about that would likely just have been told to not include the qual in their query if it's not required. However, a recent bug report indicates this might not always be possible. Bug 17540 highlighted that when we optimize Min/Max aggregates the IS NOT NULL qual that the planner adds to make the rewritten plan ignore NULLs can cause issues with poor index choice. That particular case demonstrated that other quals, especially ones where no statistics are available to allow the planner a chance at estimating an approximate selectivity for can result in poor index choice due to cheap startup paths being prefered with LIMIT 1. Here we take generic approach to fixing this by having the planner check for NOT NULL columns and just have the planner remove these quals (when they're not needed) for all queries, not just when optimizing Min/Max aggregates. Additionally, here we also detect IS NULL quals on a NOT NULL column and transform that into a gating qual so that we don't have to perform the scan at all. This also works for join relations when the Var is not nullable by any outer join. This also helps with the self-join removal work as it must replace strict join quals with IS NOT NULL quals to ensure equivalence with the original query. Author: David Rowley, Richard Guo, Andy Fan Reviewed-by: Richard Guo, David Rowley Discussion: https://postgr.es/m/CAApHDvqg6XZDhYRPz0zgOcevSMo0d3vxA9DvHrZtKfqO30WTnw@mail.gmail.com Discussion: https://postgr.es/m/17540-7aa1855ad5ec18b4%40postgresql.org --- contrib/postgres_fdw/sql/postgres_fdw.sql | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'contrib/postgres_fdw/sql/postgres_fdw.sql') diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql index 90c8fa4b705..f410c3db4e6 100644 --- a/contrib/postgres_fdw/sql/postgres_fdw.sql +++ b/contrib/postgres_fdw/sql/postgres_fdw.sql @@ -332,8 +332,8 @@ EXPLAIN (VERBOSE, COSTS OFF) SELECT * FROM ft_empty ORDER BY c1; -- =================================================================== EXPLAIN (VERBOSE, COSTS OFF) SELECT * FROM ft1 t1 WHERE t1.c1 = 1; -- Var, OpExpr(b), Const EXPLAIN (VERBOSE, COSTS OFF) SELECT * FROM ft1 t1 WHERE t1.c1 = 100 AND t1.c2 = 0; -- BoolExpr -EXPLAIN (VERBOSE, COSTS OFF) SELECT * FROM ft1 t1 WHERE c1 IS NULL; -- NullTest -EXPLAIN (VERBOSE, COSTS OFF) SELECT * FROM ft1 t1 WHERE c1 IS NOT NULL; -- NullTest +EXPLAIN (VERBOSE, COSTS OFF) SELECT * FROM ft1 t1 WHERE c3 IS NULL; -- NullTest +EXPLAIN (VERBOSE, COSTS OFF) SELECT * FROM ft1 t1 WHERE c3 IS NOT NULL; -- NullTest EXPLAIN (VERBOSE, COSTS OFF) SELECT * FROM ft1 t1 WHERE round(abs(c1), 0) = 1; -- FuncExpr EXPLAIN (VERBOSE, COSTS OFF) SELECT * FROM ft1 t1 WHERE c1 = -c1; -- OpExpr(l) EXPLAIN (VERBOSE, COSTS OFF) SELECT * FROM ft1 t1 WHERE (c1 IS NOT NULL) IS DISTINCT FROM (c1 IS NOT NULL); -- DistinctExpr -- cgit v1.2.3