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postgres_fdw: don't push down non-relabeling ArrayCoerceExpr
Commit62c3b4cd9dtaught postgres_fdw to push down ArrayCoerceExpr, but foreign_expr_walker() only recursed into the input array expression and never examined elemexpr, the per-element conversion that gives the coercion its semantics. deparseArrayCoerceExpr() then shipped a bare "arg::resulttype" cast, or nothing at all for an implicit-format coercion, leaving the remote server to re-resolve the element conversion against its own catalogs and session state. This produced wrong results or remote errors whenever the element conversion was not a plain relabeling, and it was inconsistent with how postgres_fdw treats the equivalent scalar coercions. An ArrayCoerceExpr was shipped even when its elemexpr was a cast function (whose shippability was never checked), a CoerceViaIO (e.g. float8out or byteaout, which depend on extra_float_digits / bytea_output that postgres_fdw sets differently on the remote session), or a CoerceToDomain (which pushes domain enforcement to the remote catalog). By contrast, a scalar CoerceViaIO is never shipped, and a scalar cast function is shipped only when it is shippable. Restrict pushdown to element coercions that are a plain relabeling, that is, elemexpr is a RelabelType or a bare CaseTestExpr. Any other element coercion is now evaluated locally. This keeps the common binary-coercible case pushed down, including "col = ANY($1)" with a varchar[]-to-text[] relabeling, which is the case62c3b4cd9dset out to optimize. Pushing down shippable element cast functions, to reach parity with the scalar case, is left out here for simplicity. Reported-by: Noah Misch <noah@leadboat.com> Discussion: https://postgr.es/m/20260711024234.43.noahmisch%40microsoft.com Backpatch-through: 19
This commit is contained in:
Alexander Korotkov
parent
7873db5369
commit
2349b106b6
3 changed files with 130 additions and 0 deletions
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@ -707,6 +707,26 @@ foreign_expr_walker(Node *node,
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{
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ArrayCoerceExpr *e = (ArrayCoerceExpr *) node;
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/*
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* Push down only when the per-element coercion is a plain
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* relabeling, that is, elemexpr is a RelabelType or a bare
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* CaseTestExpr. Any other element coercion -- a cast
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* function, an I/O conversion (CoerceViaIO), or a domain
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* coercion -- is kept local. We ship only a bare
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* "arg::resulttype" cast (nothing at all for an
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* implicit-format coercion), so a non-relabeling conversion
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* would be re-resolved against the remote server's catalogs
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* and session state and could silently change the result.
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* This matches the handling of the scalar coercions for the
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* I/O and domain cases (never shipped); an element cast
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* function is kept local too, which is more conservative than
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* the scalar case (a scalar cast function is shipped when it
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* is shippable).
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*/
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if (!IsA(e->elemexpr, RelabelType) &&
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!IsA(e->elemexpr, CaseTestExpr))
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return false;
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/*
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* Recurse to input subexpression.
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*/
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@ -1219,6 +1219,81 @@ EXECUTE s(ARRAY['1','2']);
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DEALLOCATE s;
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RESET plan_cache_mode;
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-- An ArrayCoerceExpr is pushed down only when its per-element coercion is
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-- a plain relabeling. An element cast function, an I/O conversion, or a
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-- domain coercion is instead evaluated locally.
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CREATE TABLE loct_acx (id int, ta text[], f8 float8[], txt text[], t text, ia int[], vc varchar[]);
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INSERT INTO loct_acx VALUES (1, '{12345}', '{0.30000000000000004}', '{0.3}', '5', '{5}', '{5}');
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CREATE FOREIGN TABLE ft_acx (id int, ta text[], f8 float8[], txt text[], t text, ia int[], vc varchar[])
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SERVER loopback OPTIONS (table_name 'loct_acx');
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-- element coercion via a cast function: not shippable, stays local
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CREATE FUNCTION acx_text2int(text) RETURNS int
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LANGUAGE plpgsql IMMUTABLE STRICT AS 'BEGIN RETURN length($1); END';
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CREATE CAST (text AS integer) WITH FUNCTION acx_text2int(text);
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EXPLAIN (VERBOSE, COSTS OFF)
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SELECT id FROM ft_acx WHERE ta::int[] = ARRAY[5];
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QUERY PLAN
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-------------------------------------------------------
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Foreign Scan on public.ft_acx
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Output: id
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Filter: ((ft_acx.ta)::integer[] = '{5}'::integer[])
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Remote SQL: SELECT id, ta FROM public.loct_acx
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(4 rows)
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DROP CAST (text AS integer);
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DROP FUNCTION acx_text2int(text);
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-- implicit-format element coercion (a cast function): stays local, and the
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-- coercion is not silently dropped from an otherwise pushed-down qual
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CREATE CAST (integer AS text) WITH FUNCTION pg_catalog.to_hex(integer) AS IMPLICIT;
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EXPLAIN (VERBOSE, COSTS OFF)
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SELECT id FROM ft_acx WHERE t = ANY (ia);
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QUERY PLAN
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-----------------------------------------------------
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Foreign Scan on public.ft_acx
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Output: id
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Filter: (ft_acx.t = ANY ((ft_acx.ia)::text[]))
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Remote SQL: SELECT id, t, ia FROM public.loct_acx
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(4 rows)
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DROP CAST (integer AS text);
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-- element coercion via a GUC-sensitive I/O conversion: stays local, so the
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-- result matches local evaluation despite the forced remote extra_float_digits
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SET extra_float_digits = 0;
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EXPLAIN (VERBOSE, COSTS OFF)
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SELECT id FROM ft_acx WHERE f8::text[] = txt;
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QUERY PLAN
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-------------------------------------------------------
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Foreign Scan on public.ft_acx
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Output: id
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Filter: ((ft_acx.f8)::text[] = ft_acx.txt)
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Remote SQL: SELECT id, f8, txt FROM public.loct_acx
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(4 rows)
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SELECT id FROM ft_acx WHERE f8::text[] = txt;
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id
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----
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1
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(1 row)
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RESET extra_float_digits;
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-- a plain relabeling element coercion (varchar[] to text[]) is still pushed down
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EXPLAIN (VERBOSE, COSTS OFF)
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SELECT id FROM ft_acx WHERE t = ANY (vc);
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QUERY PLAN
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---------------------------------------------------------------------
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Foreign Scan on public.ft_acx
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Output: id
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Remote SQL: SELECT id FROM public.loct_acx WHERE ((t = ANY (vc)))
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(3 rows)
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SELECT id FROM ft_acx WHERE t = ANY (vc);
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id
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----
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1
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(1 row)
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DROP FOREIGN TABLE ft_acx;
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DROP TABLE loct_acx;
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-- a regconfig constant referring to this text search configuration
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-- is initially unshippable
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CREATE TEXT SEARCH CONFIGURATION public.custom_search
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@ -485,6 +485,41 @@ EXECUTE s(ARRAY['1','2']);
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DEALLOCATE s;
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RESET plan_cache_mode;
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-- An ArrayCoerceExpr is pushed down only when its per-element coercion is
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-- a plain relabeling. An element cast function, an I/O conversion, or a
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-- domain coercion is instead evaluated locally.
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CREATE TABLE loct_acx (id int, ta text[], f8 float8[], txt text[], t text, ia int[], vc varchar[]);
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INSERT INTO loct_acx VALUES (1, '{12345}', '{0.30000000000000004}', '{0.3}', '5', '{5}', '{5}');
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CREATE FOREIGN TABLE ft_acx (id int, ta text[], f8 float8[], txt text[], t text, ia int[], vc varchar[])
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SERVER loopback OPTIONS (table_name 'loct_acx');
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-- element coercion via a cast function: not shippable, stays local
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CREATE FUNCTION acx_text2int(text) RETURNS int
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LANGUAGE plpgsql IMMUTABLE STRICT AS 'BEGIN RETURN length($1); END';
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CREATE CAST (text AS integer) WITH FUNCTION acx_text2int(text);
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EXPLAIN (VERBOSE, COSTS OFF)
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SELECT id FROM ft_acx WHERE ta::int[] = ARRAY[5];
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DROP CAST (text AS integer);
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DROP FUNCTION acx_text2int(text);
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-- implicit-format element coercion (a cast function): stays local, and the
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-- coercion is not silently dropped from an otherwise pushed-down qual
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CREATE CAST (integer AS text) WITH FUNCTION pg_catalog.to_hex(integer) AS IMPLICIT;
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EXPLAIN (VERBOSE, COSTS OFF)
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SELECT id FROM ft_acx WHERE t = ANY (ia);
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DROP CAST (integer AS text);
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-- element coercion via a GUC-sensitive I/O conversion: stays local, so the
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-- result matches local evaluation despite the forced remote extra_float_digits
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SET extra_float_digits = 0;
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EXPLAIN (VERBOSE, COSTS OFF)
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SELECT id FROM ft_acx WHERE f8::text[] = txt;
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SELECT id FROM ft_acx WHERE f8::text[] = txt;
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RESET extra_float_digits;
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-- a plain relabeling element coercion (varchar[] to text[]) is still pushed down
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EXPLAIN (VERBOSE, COSTS OFF)
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SELECT id FROM ft_acx WHERE t = ANY (vc);
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SELECT id FROM ft_acx WHERE t = ANY (vc);
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DROP FOREIGN TABLE ft_acx;
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DROP TABLE loct_acx;
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-- a regconfig constant referring to this text search configuration
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-- is initially unshippable
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CREATE TEXT SEARCH CONFIGURATION public.custom_search
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