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Fix mishandling of system columns in FDW queries.
postgres_fdw would send query conditions involving system columns to the remote server, even though it makes no effort to ensure that system columns other than CTID match what the remote side thinks. tableoid, in particular, probably won't match and might have some use in queries. Hence, prevent sending conditions that include non-CTID system columns. Also, create_foreignscan_plan neglected to check local restriction conditions while determining whether to set fsSystemCol for a foreign scan plan node. This again would bollix the results for queries that test a foreign table's tableoid. Back-patch the first fix to 9.3 where postgres_fdw was introduced. Back-patch the second to 9.2. The code is probably broken in 9.1 as well, but the patch doesn't apply cleanly there; given the weak state of support for FDWs in 9.1, it doesn't seem worth fixing. Etsuro Fujita, reviewed by Ashutosh Bapat, and somewhat modified by me
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‎contrib/postgres_fdw/deparse.c

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Original file line numberDiff line numberDiff line change
@@ -254,6 +254,18 @@ foreign_expr_walker(Node *node,
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var->varlevelsup == 0)
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{
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/* Var belongs to foreign table */
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/*
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* System columns other than ctid should not be sent to
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* the remote, since we don't make any effort to ensure
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* that local and remote values match (tableoid, in
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* particular, almost certainly doesn't match).
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*/
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if (var->varattno < 0 &&
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var->varattno != SelfItemPointerAttributeNumber)
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return false;
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/* Else check the collation */
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collation = var->varcollid;
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state = OidIsValid(collation) ? FDW_COLLATE_SAFE : FDW_COLLATE_NONE;
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}

‎contrib/postgres_fdw/expected/postgres_fdw.out

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@@ -826,6 +826,74 @@ DEALLOCATE st2;
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DEALLOCATE st3;
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DEALLOCATE st4;
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DEALLOCATE st5;
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-- System columns, except ctid, should not be sent to remote
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EXPLAIN (VERBOSE, COSTS false)
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SELECT * FROM ft1 t1 WHERE t1.tableoid = 'pg_class'::regclass LIMIT 1;
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QUERY PLAN
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-------------------------------------------------------------------------------
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Limit
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Output: c1, c2, c3, c4, c5, c6, c7, c8
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-> Foreign Scan on public.ft1 t1
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Output: c1, c2, c3, c4, c5, c6, c7, c8
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Filter: (t1.tableoid = 1259::oid)
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Remote SQL: SELECT "C 1", c2, c3, c4, c5, c6, c7, c8 FROM "S 1"."T 1"
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(6 rows)
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SELECT * FROM ft1 t1 WHERE t1.tableoid = 'ft1'::regclass LIMIT 1;
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c1 | c2 | c3 | c4 | c5 | c6 | c7 | c8
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----+----+-------+------------------------------+--------------------------+----+------------+-----
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1 | 1 | 00001 | Fri Jan 02 00:00:00 1970 PST | Fri Jan 02 00:00:00 1970 | 1 | 1 | foo
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(1 row)
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EXPLAIN (VERBOSE, COSTS false)
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SELECT tableoid::regclass, * FROM ft1 t1 LIMIT 1;
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QUERY PLAN
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-------------------------------------------------------------------------------
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Limit
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Output: ((tableoid)::regclass), c1, c2, c3, c4, c5, c6, c7, c8
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-> Foreign Scan on public.ft1 t1
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Output: (tableoid)::regclass, c1, c2, c3, c4, c5, c6, c7, c8
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Remote SQL: SELECT "C 1", c2, c3, c4, c5, c6, c7, c8 FROM "S 1"."T 1"
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(5 rows)
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SELECT tableoid::regclass, * FROM ft1 t1 LIMIT 1;
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tableoid | c1 | c2 | c3 | c4 | c5 | c6 | c7 | c8
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----------+----+----+-------+------------------------------+--------------------------+----+------------+-----
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ft1 | 1 | 1 | 00001 | Fri Jan 02 00:00:00 1970 PST | Fri Jan 02 00:00:00 1970 | 1 | 1 | foo
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(1 row)
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EXPLAIN (VERBOSE, COSTS false)
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SELECT * FROM ft1 t1 WHERE t1.ctid = '(0,2)';
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QUERY PLAN
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-------------------------------------------------------------------------------------------------------
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Foreign Scan on public.ft1 t1
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Output: c1, c2, c3, c4, c5, c6, c7, c8
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Remote SQL: SELECT "C 1", c2, c3, c4, c5, c6, c7, c8 FROM "S 1"."T 1" WHERE ((ctid = '(0,2)'::tid))
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(3 rows)
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SELECT * FROM ft1 t1 WHERE t1.ctid = '(0,2)';
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c1 | c2 | c3 | c4 | c5 | c6 | c7 | c8
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----+----+-------+------------------------------+--------------------------+----+------------+-----
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2 | 2 | 00002 | Sat Jan 03 00:00:00 1970 PST | Sat Jan 03 00:00:00 1970 | 2 | 2 | foo
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(1 row)
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EXPLAIN (VERBOSE, COSTS false)
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SELECT ctid, * FROM ft1 t1 LIMIT 1;
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QUERY PLAN
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-------------------------------------------------------------------------------------
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Limit
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Output: ctid, c1, c2, c3, c4, c5, c6, c7, c8
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-> Foreign Scan on public.ft1 t1
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Output: ctid, c1, c2, c3, c4, c5, c6, c7, c8
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Remote SQL: SELECT "C 1", c2, c3, c4, c5, c6, c7, c8, ctid FROM "S 1"."T 1"
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(5 rows)
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SELECT ctid, * FROM ft1 t1 LIMIT 1;
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ctid | c1 | c2 | c3 | c4 | c5 | c6 | c7 | c8
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-------+----+----+-------+------------------------------+--------------------------+----+------------+-----
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(0,1) | 1 | 1 | 00001 | Fri Jan 02 00:00:00 1970 PST | Fri Jan 02 00:00:00 1970 | 1 | 1 | foo
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(1 row)
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-- ===================================================================
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-- used in pl/pgsql function
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-- ===================================================================

‎contrib/postgres_fdw/sql/postgres_fdw.sql

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Original file line numberDiff line numberDiff line change
@@ -248,6 +248,20 @@ DEALLOCATE st3;
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DEALLOCATE st4;
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DEALLOCATE st5;
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-- System columns, except ctid, should not be sent to remote
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EXPLAIN (VERBOSE, COSTS false)
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SELECT * FROM ft1 t1 WHERE t1.tableoid = 'pg_class'::regclass LIMIT 1;
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SELECT * FROM ft1 t1 WHERE t1.tableoid = 'ft1'::regclass LIMIT 1;
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EXPLAIN (VERBOSE, COSTS false)
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SELECT tableoid::regclass, * FROM ft1 t1 LIMIT 1;
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SELECT tableoid::regclass, * FROM ft1 t1 LIMIT 1;
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EXPLAIN (VERBOSE, COSTS false)
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SELECT * FROM ft1 t1 WHERE t1.ctid = '(0,2)';
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SELECT * FROM ft1 t1 WHERE t1.ctid = '(0,2)';
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EXPLAIN (VERBOSE, COSTS false)
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SELECT ctid, * FROM ft1 t1 LIMIT 1;
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SELECT ctid, * FROM ft1 t1 LIMIT 1;
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-- ===================================================================
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-- used in pl/pgsql function
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-- ===================================================================

‎src/backend/optimizer/plan/createplan.c

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Original file line numberDiff line numberDiff line change
@@ -20,6 +20,7 @@
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#include <math.h>
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#include "access/skey.h"
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#include "access/sysattr.h"
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#include "catalog/pg_class.h"
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#include "foreign/fdwapi.h"
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#include "miscadmin.h"
@@ -1945,6 +1946,8 @@ create_foreignscan_plan(PlannerInfo *root, ForeignPath *best_path,
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RelOptInfo *rel = best_path->path.parent;
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Index scan_relid = rel->relid;
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RangeTblEntry *rte;
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Bitmapset *attrs_used = NULL;
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ListCell *lc;
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int i;
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/* it should be a base rel... */
@@ -1992,17 +1995,34 @@ create_foreignscan_plan(PlannerInfo *root, ForeignPath *best_path,
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* Detect whether any system columns are requested from rel. This is a
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* bit of a kluge and might go away someday, so we intentionally leave it
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* out of the API presented to FDWs.
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*
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* First, examine all the attributes needed for joins or final output.
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* Note: we must look at reltargetlist, not the attr_needed data, because
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* attr_needed isn't computed for inheritance child rels.
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*/
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pull_varattnos((Node *) rel->reltargetlist, rel->relid, &attrs_used);
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/* Add all the attributes used by restriction clauses. */
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foreach(lc, rel->baserestrictinfo)
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{
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RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
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pull_varattnos((Node *) rinfo->clause, rel->relid, &attrs_used);
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}
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/* Now, are any system columns requested from rel? */
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scan_plan->fsSystemCol = false;
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for (i = rel->min_attr; i < 0; i++)
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for (i = FirstLowInvalidHeapAttributeNumber + 1; i < 0; i++)
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{
1999-
if (!bms_is_empty(rel->attr_needed[i - rel->min_attr]))
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if (bms_is_member(i - FirstLowInvalidHeapAttributeNumber, attrs_used))
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{
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scan_plan->fsSystemCol = true;
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break;
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}
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}
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bms_free(attrs_used);
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return scan_plan;
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}
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