Fix a crash in logical replication

The bug was that determining which columns are part of the replica
identity index using RelationGetIndexAttrBitmap() would run
eval_const_expressions() on index expressions and predicates across
all indexes of the table, which in turn might require a snapshot, but
there wasn't one set, so it crashes.  There were actually two separate
bugs, one on the publisher and one on the subscriber.

To trigger the bug, a table that is part of a publication or
subscription needs to have an index with a predicate or expression
that lends itself to constant expressions simplification.

The fix is to avoid the constant expressions simplification in
RelationGetIndexAttrBitmap(), so that it becomes safe to call in these
contexts.  The constant expressions simplification comes from the
calls to RelationGetIndexExpressions()/RelationGetIndexPredicate() via
BuildIndexInfo().  But RelationGetIndexAttrBitmap() calling
BuildIndexInfo() is overkill.  The latter just takes pg_index catalog
information, packs it into the IndexInfo structure, which former then
just unpacks again and throws away.  We can just do this directly with
less overhead and skip the troublesome calls to
eval_const_expressions().  This also removes the awkward
cross-dependency between relcache.c and index.c.

Bug: #15114
Reported-by: Петър Славов <pet.slavov@gmail.com>
Reviewed-by: Noah Misch <noah@leadboat.com>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://www.postgresql.org/message-id/flat/152110589574.1223.17983600132321618383@wrigleys.postgresql.org/

Author: petere

src/backend/utils/cache/relcache.c

@@ -40,7 +40,6 @@
 #include "access/xact.h"
 #include "access/xlog.h"
 #include "catalog/catalog.h"
-#include "catalog/index.h"
 #include "catalog/indexing.h"
 #include "catalog/namespace.h"
 #include "catalog/partition.h"
@@ -4700,12 +4699,12 @@ RelationGetIndexPredicate(Relation relation)
  * 2. "recheck_on_update" index option explicitly set by user, which overrides 1)
  */
 static bool
-IsProjectionFunctionalIndex(Relation index, IndexInfo *ii)
+IsProjectionFunctionalIndex(Relation index)
 {
 	bool		is_projection = false;
 
 #ifdef NOT_USED
-	if (ii->ii_Expressions)
+	if (RelationGetIndexExpressions(index))
 	{
 		HeapTuple	tuple;
 		Datum		reloptions;
@@ -4715,7 +4714,7 @@ IsProjectionFunctionalIndex(Relation index, IndexInfo *ii)
 		/* by default functional index is considered as non-injective */
 		is_projection = true;
 
-		cost_qual_eval(&index_expr_cost, ii->ii_Expressions, NULL);
+		cost_qual_eval(&index_expr_cost, RelationGetIndexExpressions(index), NULL);
 
 		/*
 		 * If index expression is too expensive, then disable projection
@@ -4861,21 +4860,44 @@ RelationGetIndexAttrBitmap(Relation relation, IndexAttrBitmapKind attrKind)
 	{
 		Oid			indexOid = lfirst_oid(l);
 		Relation	indexDesc;
-		IndexInfo  *indexInfo;
+		Datum		datum;
+		bool		isnull;
+		Node	   *indexExpressions;
+		Node	   *indexPredicate;
 		int			i;
 		bool		isKey;		/* candidate key */
 		bool		isPK;		/* primary key */
 		bool		isIDKey;	/* replica identity index */
 
 		indexDesc = index_open(indexOid, AccessShareLock);
 
-		/* Extract index key information from the index's pg_index row */
-		indexInfo = BuildIndexInfo(indexDesc);
+		/*
+		 * Extract index expressions and index predicate.  Note: Don't use
+		 * RelationGetIndexExpressions()/RelationGetIndexPredicate(), because
+		 * those might run constant expressions evaluation, which needs a
+		 * snapshot, which we might not have here.  (Also, it's probably more
+		 * sound to collect the bitmaps before any transformations that might
+		 * eliminate columns, but the practical impact of this is limited.)
+		 */
+
+		datum = heap_getattr(indexDesc->rd_indextuple, Anum_pg_index_indexprs,
+							 GetPgIndexDescriptor(), &isnull);
+		if (!isnull)
+			indexExpressions = stringToNode(TextDatumGetCString(datum));
+		else
+			indexExpressions = NULL;
+
+		datum = heap_getattr(indexDesc->rd_indextuple, Anum_pg_index_indpred,
+							 GetPgIndexDescriptor(), &isnull);
+		if (!isnull)
+			indexPredicate = stringToNode(TextDatumGetCString(datum));
+		else
+			indexPredicate = NULL;
 
 		/* Can this index be referenced by a foreign key? */
-		isKey = indexInfo->ii_Unique &&
-			indexInfo->ii_Expressions == NIL &&
-			indexInfo->ii_Predicate == NIL;
+		isKey = indexDesc->rd_index->indisunique &&
+			indexExpressions == NULL &&
+			indexPredicate == NULL;
 
 		/* Is this a primary key? */
 		isPK = (indexOid == relpkindex);
@@ -4884,9 +4906,9 @@ RelationGetIndexAttrBitmap(Relation relation, IndexAttrBitmapKind attrKind)
 		isIDKey = (indexOid == relreplindex);
 
 		/* Collect simple attribute references */
-		for (i = 0; i < indexInfo->ii_NumIndexAttrs; i++)
+		for (i = 0; i < indexDesc->rd_index->indnatts; i++)
 		{
-			int			attrnum = indexInfo->ii_IndexAttrNumbers[i];
+			int			attrnum = indexDesc->rd_index->indkey.values[i];
 
 			/*
 			 * Since we have covering indexes with non-key columns, we must
@@ -4901,33 +4923,33 @@ RelationGetIndexAttrBitmap(Relation relation, IndexAttrBitmapKind attrKind)
 				indexattrs = bms_add_member(indexattrs,
 											attrnum - FirstLowInvalidHeapAttributeNumber);
 
-				if (isKey && i < indexInfo->ii_NumIndexKeyAttrs)
+				if (isKey && i < indexDesc->rd_index->indnkeyatts)
 					uindexattrs = bms_add_member(uindexattrs,
 												 attrnum - FirstLowInvalidHeapAttributeNumber);
 
-				if (isPK && i < indexInfo->ii_NumIndexKeyAttrs)
+				if (isPK && i < indexDesc->rd_index->indnkeyatts)
 					pkindexattrs = bms_add_member(pkindexattrs,
 												  attrnum - FirstLowInvalidHeapAttributeNumber);
 
-				if (isIDKey && i < indexInfo->ii_NumIndexKeyAttrs)
+				if (isIDKey && i < indexDesc->rd_index->indnkeyatts)
 					idindexattrs = bms_add_member(idindexattrs,
 												  attrnum - FirstLowInvalidHeapAttributeNumber);
 			}
 		}
 
 		/* Collect attributes used in expressions, too */
-		if (IsProjectionFunctionalIndex(indexDesc, indexInfo))
+		if (IsProjectionFunctionalIndex(indexDesc))
 		{
 			projindexes = bms_add_member(projindexes, indexno);
-			pull_varattnos((Node *) indexInfo->ii_Expressions, 1, &projindexattrs);
+			pull_varattnos(indexExpressions, 1, &projindexattrs);
 		}
 		else
 		{
 			/* Collect all attributes used in expressions, too */
-			pull_varattnos((Node *) indexInfo->ii_Expressions, 1, &indexattrs);
+			pull_varattnos(indexExpressions, 1, &indexattrs);
 		}
 		/* Collect all attributes in the index predicate, too */
-		pull_varattnos((Node *) indexInfo->ii_Predicate, 1, &indexattrs);
+		pull_varattnos(indexPredicate, 1, &indexattrs);
 
 		index_close(indexDesc, AccessShareLock);
 		indexno += 1;

src/test/subscription/t/100_bugs.pl

@@ -0,0 +1,65 @@
+# Tests for various bugs found over time
+use strict;
+use warnings;
+use PostgresNode;
+use TestLib;
+use Test::More tests => 1;
+
+# Bug #15114
+
+# The bug was that determining which columns are part of the replica
+# identity index using RelationGetIndexAttrBitmap() would run
+# eval_const_expressions() on index expressions and predicates across
+# all indexes of the table, which in turn might require a snapshot,
+# but there wasn't one set, so it crashes.  There were actually two
+# separate bugs, one on the publisher and one on the subscriber.  The
+# fix was to avoid the constant expressions simplification in
+# RelationGetIndexAttrBitmap(), so it's safe to call in more contexts.
+
+my $node_publisher = get_new_node('publisher');
+$node_publisher->init(allows_streaming => 'logical');
+$node_publisher->start;
+
+my $node_subscriber = get_new_node('subscriber');
+$node_subscriber->init(allows_streaming => 'logical');
+$node_subscriber->start;
+
+my $publisher_connstr = $node_publisher->connstr . ' dbname=postgres';
+
+$node_publisher->safe_psql('postgres',
+	"CREATE TABLE tab1 (a int PRIMARY KEY, b int)");
+
+$node_publisher->safe_psql('postgres',
+	"CREATE FUNCTION double(x int) RETURNS int IMMUTABLE LANGUAGE SQL AS 'select x * 2'");
+
+# an index with a predicate that lends itself to constant expressions
+# evaluation
+$node_publisher->safe_psql('postgres',
+	"CREATE INDEX ON tab1 (b) WHERE a > double(1)");
+
+# and the same setup on the subscriber
+$node_subscriber->safe_psql('postgres',
+	"CREATE TABLE tab1 (a int PRIMARY KEY, b int)");
+
+$node_subscriber->safe_psql('postgres',
+	"CREATE FUNCTION double(x int) RETURNS int IMMUTABLE LANGUAGE SQL AS 'select x * 2'");
+
+$node_subscriber->safe_psql('postgres',
+	"CREATE INDEX ON tab1 (b) WHERE a > double(1)");
+
+$node_publisher->safe_psql('postgres',
+	"CREATE PUBLICATION pub1 FOR ALL TABLES");
+
+$node_subscriber->safe_psql('postgres',
+	"CREATE SUBSCRIPTION sub1 CONNECTION '$publisher_connstr application_name=sub1' PUBLICATION pub1");
+
+$node_publisher->wait_for_catchup('sub1');
+
+# This would crash, first on the publisher, and then (if the publisher
+# is fixed) on the subscriber.
+$node_publisher->safe_psql('postgres',
+	"INSERT INTO tab1 VALUES (1, 2)");
+
+$node_publisher->wait_for_catchup('sub1');
+
+pass('index predicates do not cause crash');