From c34df8a003c3e478d70e8251bd2a24d710b297d4 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sat, 16 Apr 2016 12:11:41 -0400
Subject: [PATCH] Disallow creation of indexes on system columns (except for
 OID).

Although OID acts pretty much like user data, the other system columns do
not, so an index on one would likely misbehave.  And it's pretty hard to
see a use-case for one, anyway.  Let's just forbid the case rather than
worry about whether it should be supported.

David Rowley
---
 src/backend/commands/indexcmds.c           | 37 ++++++++++++++++++++++
 src/test/regress/expected/create_index.out | 16 ++++++++++
 src/test/regress/sql/create_index.sql      | 19 +++++++++++
 3 files changed, 72 insertions(+)

diff --git a/src/backend/commands/indexcmds.c b/src/backend/commands/indexcmds.c
index 13b04e68f0..d14d540b26 100644
--- a/src/backend/commands/indexcmds.c
+++ b/src/backend/commands/indexcmds.c
@@ -18,6 +18,7 @@
 #include "access/amapi.h"
 #include "access/htup_details.h"
 #include "access/reloptions.h"
+#include "access/sysattr.h"
 #include "access/xact.h"
 #include "catalog/catalog.h"
 #include "catalog/index.h"
@@ -37,6 +38,7 @@
 #include "nodes/nodeFuncs.h"
 #include "optimizer/clauses.h"
 #include "optimizer/planner.h"
+#include "optimizer/var.h"
 #include "parser/parse_coerce.h"
 #include "parser/parse_func.h"
 #include "parser/parse_oper.h"
@@ -574,6 +576,41 @@ DefineIndex(Oid relationId,
 	if (stmt->primary)
 		index_check_primary_key(rel, indexInfo, is_alter_table);
 
+	/*
+	 * We disallow indexes on system columns other than OID.  They would not
+	 * necessarily get updated correctly, and they don't seem useful anyway.
+	 */
+	for (i = 0; i < indexInfo->ii_NumIndexAttrs; i++)
+	{
+		AttrNumber	attno = indexInfo->ii_KeyAttrNumbers[i];
+
+		if (attno < 0 && attno != ObjectIdAttributeNumber)
+			ereport(ERROR,
+					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+			   errmsg("index creation on system columns is not supported")));
+	}
+
+	/*
+	 * Also check for system columns used in expressions or predicates.
+	 */
+	if (indexInfo->ii_Expressions || indexInfo->ii_Predicate)
+	{
+		Bitmapset  *indexattrs = NULL;
+
+		pull_varattnos((Node *) indexInfo->ii_Expressions, 1, &indexattrs);
+		pull_varattnos((Node *) indexInfo->ii_Predicate, 1, &indexattrs);
+
+		for (i = FirstLowInvalidHeapAttributeNumber + 1; i < 0; i++)
+		{
+			if (i != ObjectIdAttributeNumber &&
+				bms_is_member(i - FirstLowInvalidHeapAttributeNumber,
+							  indexattrs))
+				ereport(ERROR,
+						(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				errmsg("index creation on system columns is not supported")));
+		}
+	}
+
 	/*
 	 * Report index creation if appropriate (delay this till after most of the
 	 * error checks)
diff --git a/src/test/regress/expected/create_index.out b/src/test/regress/expected/create_index.out
index b72e65d1bd..97cc49e623 100644
--- a/src/test/regress/expected/create_index.out
+++ b/src/test/regress/expected/create_index.out
@@ -2541,6 +2541,22 @@ ERROR:  cannot drop index cwi_replaced_pkey because constraint cwi_replaced_pkey
 HINT:  You can drop constraint cwi_replaced_pkey on table cwi_test instead.
 DROP TABLE cwi_test;
 --
+-- Check handling of indexes on system columns
+--
+CREATE TABLE oid_table (a INT) WITH OIDS;
+-- An index on the OID column should be allowed
+CREATE INDEX ON oid_table (oid);
+-- Other system columns cannot be indexed
+CREATE INDEX ON oid_table (ctid);
+ERROR:  index creation on system columns is not supported
+-- nor used in expressions
+CREATE INDEX ON oid_table ((ctid >= '(1000,0)'));
+ERROR:  index creation on system columns is not supported
+-- nor used in predicates
+CREATE INDEX ON oid_table (a) WHERE ctid >= '(1000,0)';
+ERROR:  index creation on system columns is not supported
+DROP TABLE oid_table;
+--
 -- Tests for IS NULL/IS NOT NULL with b-tree indexes
 --
 SELECT unique1, unique2 INTO onek_with_null FROM onek;
diff --git a/src/test/regress/sql/create_index.sql b/src/test/regress/sql/create_index.sql
index ff8695361c..7c582ea810 100644
--- a/src/test/regress/sql/create_index.sql
+++ b/src/test/regress/sql/create_index.sql
@@ -824,6 +824,25 @@ DROP INDEX cwi_replaced_pkey;	-- Should fail; a constraint depends on it
 
 DROP TABLE cwi_test;
 
+--
+-- Check handling of indexes on system columns
+--
+CREATE TABLE oid_table (a INT) WITH OIDS;
+
+-- An index on the OID column should be allowed
+CREATE INDEX ON oid_table (oid);
+
+-- Other system columns cannot be indexed
+CREATE INDEX ON oid_table (ctid);
+
+-- nor used in expressions
+CREATE INDEX ON oid_table ((ctid >= '(1000,0)'));
+
+-- nor used in predicates
+CREATE INDEX ON oid_table (a) WHERE ctid >= '(1000,0)';
+
+DROP TABLE oid_table;
+
 --
 -- Tests for IS NULL/IS NOT NULL with b-tree indexes
 --