Commit
62c3b4cd9ddc taught 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 case
62c3b4cd9ddc set 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
{
ArrayCoerceExpr *e = (ArrayCoerceExpr *) node;
+ /*
+ * Push down only when the per-element coercion is a plain
+ * relabeling, that is, elemexpr is a RelabelType or a bare
+ * CaseTestExpr. Any other element coercion -- a cast
+ * function, an I/O conversion (CoerceViaIO), or a domain
+ * coercion -- is kept local. We ship only a bare
+ * "arg::resulttype" cast (nothing at all for an
+ * implicit-format coercion), so a non-relabeling conversion
+ * would be re-resolved against the remote server's catalogs
+ * and session state and could silently change the result.
+ * This matches the handling of the scalar coercions for the
+ * I/O and domain cases (never shipped); an element cast
+ * function is kept local too, which is more conservative than
+ * the scalar case (a scalar cast function is shipped when it
+ * is shippable).
+ */
+ if (!IsA(e->elemexpr, RelabelType) &&
+ !IsA(e->elemexpr, CaseTestExpr))
+ return false;
+
/*
* Recurse to input subexpression.
*/
DEALLOCATE s;
RESET plan_cache_mode;
+-- An ArrayCoerceExpr is pushed down only when its per-element coercion is
+-- a plain relabeling. An element cast function, an I/O conversion, or a
+-- domain coercion is instead evaluated locally.
+CREATE TABLE loct_acx (id int, ta text[], f8 float8[], txt text[], t text, ia int[], vc varchar[]);
+INSERT INTO loct_acx VALUES (1, '{12345}', '{0.30000000000000004}', '{0.3}', '5', '{5}', '{5}');
+CREATE FOREIGN TABLE ft_acx (id int, ta text[], f8 float8[], txt text[], t text, ia int[], vc varchar[])
+ SERVER loopback OPTIONS (table_name 'loct_acx');
+-- element coercion via a cast function: not shippable, stays local
+CREATE FUNCTION acx_text2int(text) RETURNS int
+ LANGUAGE plpgsql IMMUTABLE STRICT AS 'BEGIN RETURN length($1); END';
+CREATE CAST (text AS integer) WITH FUNCTION acx_text2int(text);
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT id FROM ft_acx WHERE ta::int[] = ARRAY[5];
+ QUERY PLAN
+-------------------------------------------------------
+ Foreign Scan on public.ft_acx
+ Output: id
+ Filter: ((ft_acx.ta)::integer[] = '{5}'::integer[])
+ Remote SQL: SELECT id, ta FROM public.loct_acx
+(4 rows)
+
+DROP CAST (text AS integer);
+DROP FUNCTION acx_text2int(text);
+-- implicit-format element coercion (a cast function): stays local, and the
+-- coercion is not silently dropped from an otherwise pushed-down qual
+CREATE CAST (integer AS text) WITH FUNCTION pg_catalog.to_hex(integer) AS IMPLICIT;
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT id FROM ft_acx WHERE t = ANY (ia);
+ QUERY PLAN
+-----------------------------------------------------
+ Foreign Scan on public.ft_acx
+ Output: id
+ Filter: (ft_acx.t = ANY ((ft_acx.ia)::text[]))
+ Remote SQL: SELECT id, t, ia FROM public.loct_acx
+(4 rows)
+
+DROP CAST (integer AS text);
+-- element coercion via a GUC-sensitive I/O conversion: stays local, so the
+-- result matches local evaluation despite the forced remote extra_float_digits
+SET extra_float_digits = 0;
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT id FROM ft_acx WHERE f8::text[] = txt;
+ QUERY PLAN
+-------------------------------------------------------
+ Foreign Scan on public.ft_acx
+ Output: id
+ Filter: ((ft_acx.f8)::text[] = ft_acx.txt)
+ Remote SQL: SELECT id, f8, txt FROM public.loct_acx
+(4 rows)
+
+SELECT id FROM ft_acx WHERE f8::text[] = txt;
+ id
+----
+ 1
+(1 row)
+
+RESET extra_float_digits;
+-- a plain relabeling element coercion (varchar[] to text[]) is still pushed down
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT id FROM ft_acx WHERE t = ANY (vc);
+ QUERY PLAN
+---------------------------------------------------------------------
+ Foreign Scan on public.ft_acx
+ Output: id
+ Remote SQL: SELECT id FROM public.loct_acx WHERE ((t = ANY (vc)))
+(3 rows)
+
+SELECT id FROM ft_acx WHERE t = ANY (vc);
+ id
+----
+ 1
+(1 row)
+
+DROP FOREIGN TABLE ft_acx;
+DROP TABLE loct_acx;
-- a regconfig constant referring to this text search configuration
-- is initially unshippable
CREATE TEXT SEARCH CONFIGURATION public.custom_search
DEALLOCATE s;
RESET plan_cache_mode;
+-- An ArrayCoerceExpr is pushed down only when its per-element coercion is
+-- a plain relabeling. An element cast function, an I/O conversion, or a
+-- domain coercion is instead evaluated locally.
+CREATE TABLE loct_acx (id int, ta text[], f8 float8[], txt text[], t text, ia int[], vc varchar[]);
+INSERT INTO loct_acx VALUES (1, '{12345}', '{0.30000000000000004}', '{0.3}', '5', '{5}', '{5}');
+CREATE FOREIGN TABLE ft_acx (id int, ta text[], f8 float8[], txt text[], t text, ia int[], vc varchar[])
+ SERVER loopback OPTIONS (table_name 'loct_acx');
+-- element coercion via a cast function: not shippable, stays local
+CREATE FUNCTION acx_text2int(text) RETURNS int
+ LANGUAGE plpgsql IMMUTABLE STRICT AS 'BEGIN RETURN length($1); END';
+CREATE CAST (text AS integer) WITH FUNCTION acx_text2int(text);
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT id FROM ft_acx WHERE ta::int[] = ARRAY[5];
+DROP CAST (text AS integer);
+DROP FUNCTION acx_text2int(text);
+-- implicit-format element coercion (a cast function): stays local, and the
+-- coercion is not silently dropped from an otherwise pushed-down qual
+CREATE CAST (integer AS text) WITH FUNCTION pg_catalog.to_hex(integer) AS IMPLICIT;
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT id FROM ft_acx WHERE t = ANY (ia);
+DROP CAST (integer AS text);
+-- element coercion via a GUC-sensitive I/O conversion: stays local, so the
+-- result matches local evaluation despite the forced remote extra_float_digits
+SET extra_float_digits = 0;
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT id FROM ft_acx WHERE f8::text[] = txt;
+SELECT id FROM ft_acx WHERE f8::text[] = txt;
+RESET extra_float_digits;
+-- a plain relabeling element coercion (varchar[] to text[]) is still pushed down
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT id FROM ft_acx WHERE t = ANY (vc);
+SELECT id FROM ft_acx WHERE t = ANY (vc);
+DROP FOREIGN TABLE ft_acx;
+DROP TABLE loct_acx;
+
-- a regconfig constant referring to this text search configuration
-- is initially unshippable
CREATE TEXT SEARCH CONFIGURATION public.custom_search
projects / thirdparty / postgresql.git / commitdiff
