pageinspect: Fix failure with hash_bitmap_info() for partitioned indexes

This function reads directly a page from a relation, relying on
index_open() to open the index to read from.  Unfortunately, this would
crash when using partitioned indexes, as these can be opened with
index_open() but they have no physical pages.

Alexander has fixed the module, while I have written the test.

Author: Alexander Lakhin, Michael Paquier
Discussion: https://postgr.es/m/18246-f4d9ff7cb3af77e6@postgresql.org
Backpatch-through: 12

Author: michaelpq

contrib/pageinspect/expected/hash.out

@@ -1,6 +1,8 @@
 CREATE TABLE test_hash (a int, b text);
 INSERT INTO test_hash VALUES (1, 'one');
 CREATE INDEX test_hash_a_idx ON test_hash USING hash (a);
+CREATE TABLE test_hash_part (a int, b int) PARTITION BY RANGE (a);
+CREATE INDEX test_hash_part_idx ON test_hash_part USING hash(b);
 \x
 SELECT hash_page_type(get_raw_page('test_hash_a_idx', 0));
 -[ RECORD 1 ]--+---------
@@ -44,6 +46,8 @@ SELECT * FROM hash_bitmap_info('test_hash_a_idx', 5);
 ERROR:  invalid overflow block number 5
 SELECT * FROM hash_bitmap_info('test_hash_a_idx', 6);
 ERROR:  block number 6 is out of range for relation "test_hash_a_idx"
+SELECT * FROM hash_bitmap_info('test_hash_part_idx', 1); -- error
+ERROR:  "test_hash_part_idx" is not a hash index
 SELECT magic, version, ntuples, bsize, bmsize, bmshift, maxbucket, highmask,
 lowmask, ovflpoint, firstfree, nmaps, procid, spares, mapp FROM
 hash_metapage_info(get_raw_page('test_hash_a_idx', 0));
@@ -203,3 +207,4 @@ SELECT hash_page_type(decode(repeat('00', :block_size), 'hex'));
 hash_page_type | unused
 
 DROP TABLE test_hash;
+DROP TABLE test_hash_part;

contrib/pageinspect/hashfuncs.c

@@ -12,6 +12,7 @@
 
 #include "access/hash.h"
 #include "access/htup_details.h"
+#include "access/relation.h"
 #include "catalog/pg_am.h"
 #include "catalog/pg_type.h"
 #include "funcapi.h"
@@ -27,6 +28,7 @@ PG_FUNCTION_INFO_V1(hash_page_items);
 PG_FUNCTION_INFO_V1(hash_bitmap_info);
 PG_FUNCTION_INFO_V1(hash_metapage_info);
 
+#define IS_INDEX(r) ((r)->rd_rel->relkind == RELKIND_INDEX)
 #define IS_HASH(r) ((r)->rd_rel->relam == HASH_AM_OID)
 
 /* ------------------------------------------------
@@ -413,9 +415,9 @@ hash_bitmap_info(PG_FUNCTION_ARGS)
 				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
 				 errmsg("must be superuser to use raw page functions")));
 
-	indexRel = index_open(indexRelid, AccessShareLock);
+	indexRel = relation_open(indexRelid, AccessShareLock);
 
-	if (!IS_HASH(indexRel))
+	if (!IS_INDEX(indexRel) || !IS_HASH(indexRel))
 		ereport(ERROR,
 				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
 				 errmsg("\"%s\" is not a %s index",

contrib/pageinspect/sql/hash.sql

@@ -2,6 +2,9 @@ CREATE TABLE test_hash (a int, b text);
 INSERT INTO test_hash VALUES (1, 'one');
 CREATE INDEX test_hash_a_idx ON test_hash USING hash (a);
 
+CREATE TABLE test_hash_part (a int, b int) PARTITION BY RANGE (a);
+CREATE INDEX test_hash_part_idx ON test_hash_part USING hash(b);
+
 \x
 
 SELECT hash_page_type(get_raw_page('test_hash_a_idx', 0));
@@ -21,6 +24,7 @@ SELECT * FROM hash_bitmap_info('test_hash_a_idx', 3);
 SELECT * FROM hash_bitmap_info('test_hash_a_idx', 4);
 SELECT * FROM hash_bitmap_info('test_hash_a_idx', 5);
 SELECT * FROM hash_bitmap_info('test_hash_a_idx', 6);
+SELECT * FROM hash_bitmap_info('test_hash_part_idx', 1); -- error
 
 
 SELECT magic, version, ntuples, bsize, bmsize, bmshift, maxbucket, highmask,
@@ -106,3 +110,4 @@ SELECT hash_page_stats(decode(repeat('00', :block_size), 'hex'));
 SELECT hash_page_type(decode(repeat('00', :block_size), 'hex'));
 
 DROP TABLE test_hash;
+DROP TABLE test_hash_part;