Fix multiple bugs in contrib/pgstattuple's pgstatindex() function.

Dead or half-dead index leaf pages were incorrectly reported as live, as a
consequence of a code rearrangement I made (during a moment of severe brain
fade, evidently) in commit d287818eb514d431.

The index metapage was not counted in index_size, causing that result to
not agree with the actual index size on-disk.

Index root pages were not counted in internal_pages, which is inconsistent
compared to the case of a root that's also a leaf (one-page index), where
the root would be counted in leaf_pages.  Aside from that inconsistency,
this could lead to additional transient discrepancies between the reported
page counts and index_size, since it's possible for pgstatindex's scan to
see zero or multiple pages marked as BTP_ROOT, if the root moves due to
a split during the scan.  With these fixes, index_size will always be
exactly one page more than the sum of the displayed page counts.

Also, the index_size result was incorrectly documented as being measured in
pages; it's always been measured in bytes.  (While fixing that, I couldn't
resist doing some small additional wordsmithing on the pgstattuple docs.)

Including the metapage causes the reported index_size to not be zero for
an empty index.  To preserve the desired property that the pgstattuple
regression test results are platform-independent (ie, BLCKSZ configuration
independent), scale the index_size result in the regression tests.

The documentation issue was reported by Otsuka Kenji, and the inconsistent
root page counting by Peter Geoghegan; the other problems noted by me.
Back-patch to all supported branches, because this has been broken for
a long time.

3 files changed, 50 insertions, 36 deletions

diff --git a/contrib/pgstattuple/expected/pgstattuple.out b/contrib/pgstattuple/expected/pgstattuple.out
index d769f6d4943..e920234488e 100644
--- a/contrib/pgstattuple/expected/pgstattuple.out
+++ b/contrib/pgstattuple/expected/pgstattuple.out
@@ -41,40 +41,44 @@ select pgstattuple(relname) from pg_class where relname = 'test';
  (0,0,0,0,0,0,0,0,0)
 (1 row)
 
-select * from pgstatindex('test_pkey');
+select version, tree_level,
+    index_size / current_setting('block_size')::int as index_size,
+    root_block_no, internal_pages, leaf_pages, empty_pages, deleted_pages,
+    avg_leaf_density, leaf_fragmentation
+    from pgstatindex('test_pkey');
  version | tree_level | index_size | root_block_no | internal_pages | leaf_pages | empty_pages | deleted_pages | avg_leaf_density | leaf_fragmentation 
 ---------+------------+------------+---------------+----------------+------------+-------------+---------------+------------------+--------------------
-       2 |          0 |          0 |             0 |              0 |          0 |           0 |             0 |              NaN |                NaN
+       2 |          0 |          1 |             0 |              0 |          0 |           0 |             0 |              NaN |                NaN
 (1 row)
 
-select * from pgstatindex('test_pkey'::text);
+select version, tree_level,
+    index_size / current_setting('block_size')::int as index_size,
+    root_block_no, internal_pages, leaf_pages, empty_pages, deleted_pages,
+    avg_leaf_density, leaf_fragmentation
+    from pgstatindex('test_pkey'::text);
  version | tree_level | index_size | root_block_no | internal_pages | leaf_pages | empty_pages | deleted_pages | avg_leaf_density | leaf_fragmentation 
 ---------+------------+------------+---------------+----------------+------------+-------------+---------------+------------------+--------------------
-       2 |          0 |          0 |             0 |              0 |          0 |           0 |             0 |              NaN |                NaN
+       2 |          0 |          1 |             0 |              0 |          0 |           0 |             0 |              NaN |                NaN
 (1 row)
 
-select * from pgstatindex('test_pkey'::name);
+select version, tree_level,
+    index_size / current_setting('block_size')::int as index_size,
+    root_block_no, internal_pages, leaf_pages, empty_pages, deleted_pages,
+    avg_leaf_density, leaf_fragmentation
+    from pgstatindex('test_pkey'::name);
  version | tree_level | index_size | root_block_no | internal_pages | leaf_pages | empty_pages | deleted_pages | avg_leaf_density | leaf_fragmentation 
 ---------+------------+------------+---------------+----------------+------------+-------------+---------------+------------------+--------------------
-       2 |          0 |          0 |             0 |              0 |          0 |           0 |             0 |              NaN |                NaN
+       2 |          0 |          1 |             0 |              0 |          0 |           0 |             0 |              NaN |                NaN
 (1 row)
 
-select * from pgstatindex('test_pkey'::regclass);
+select version, tree_level,
+    index_size / current_setting('block_size')::int as index_size,
+    root_block_no, internal_pages, leaf_pages, empty_pages, deleted_pages,
+    avg_leaf_density, leaf_fragmentation
+    from pgstatindex('test_pkey'::regclass);
  version | tree_level | index_size | root_block_no | internal_pages | leaf_pages | empty_pages | deleted_pages | avg_leaf_density | leaf_fragmentation 
 ---------+------------+------------+---------------+----------------+------------+-------------+---------------+------------------+--------------------
-       2 |          0 |          0 |             0 |              0 |          0 |           0 |             0 |              NaN |                NaN
-(1 row)
-
-select pgstatindex(oid) from pg_class where relname = 'test_pkey';
-        pgstatindex        
----------------------------
- (2,0,0,0,0,0,0,0,NaN,NaN)
-(1 row)
-
-select pgstatindex(relname) from pg_class where relname = 'test_pkey';
-        pgstatindex        
----------------------------
- (2,0,0,0,0,0,0,0,NaN,NaN)
+       2 |          0 |          1 |             0 |              0 |          0 |           0 |             0 |              NaN |                NaN
 (1 row)
 
 select pg_relpages('test');
diff --git a/contrib/pgstattuple/pgstatindex.c b/contrib/pgstattuple/pgstatindex.c
index 8048a2cbe7c..9f1377c4cd9 100644
--- a/contrib/pgstattuple/pgstatindex.c
+++ b/contrib/pgstattuple/pgstatindex.c
@@ -79,7 +79,6 @@ typedef struct BTIndexStat
 	uint32		level;
 	BlockNumber root_blkno;
 
-	uint64		root_pages;
 	uint64		internal_pages;
 	uint64		leaf_pages;
 	uint64		empty_pages;
@@ -185,7 +184,6 @@ pgstatindex_impl(Relation rel, FunctionCallInfo fcinfo)
 	}
 
 	/* -- init counters -- */
-	indexStat.root_pages = 0;
 	indexStat.internal_pages = 0;
 	indexStat.leaf_pages = 0;
 	indexStat.empty_pages = 0;
@@ -218,7 +216,11 @@ pgstatindex_impl(Relation rel, FunctionCallInfo fcinfo)
 
 		/* Determine page type, and update totals */
 
-		if (P_ISLEAF(opaque))
+		if (P_ISDELETED(opaque))
+			indexStat.deleted_pages++;
+		else if (P_IGNORE(opaque))
+			indexStat.empty_pages++;	/* this is the "half dead" state */
+		else if (P_ISLEAF(opaque))
 		{
 			int			max_avail;
 
@@ -235,12 +237,6 @@ pgstatindex_impl(Relation rel, FunctionCallInfo fcinfo)
 			if (opaque->btpo_next != P_NONE && opaque->btpo_next < blkno)
 				indexStat.fragments++;
 		}
-		else if (P_ISDELETED(opaque))
-			indexStat.deleted_pages++;
-		else if (P_IGNORE(opaque))
-			indexStat.empty_pages++;
-		else if (P_ISROOT(opaque))
-			indexStat.root_pages++;
 		else
 			indexStat.internal_pages++;
 
@@ -269,7 +265,7 @@ pgstatindex_impl(Relation rel, FunctionCallInfo fcinfo)
 		values[j++] = psprintf("%d", indexStat.version);
 		values[j++] = psprintf("%d", indexStat.level);
 		values[j++] = psprintf(INT64_FORMAT,
-							   (indexStat.root_pages +
+							   (1 +		/* include the metapage in index_size */
 								indexStat.leaf_pages +
 								indexStat.internal_pages +
 								indexStat.deleted_pages +
diff --git a/contrib/pgstattuple/sql/pgstattuple.sql b/contrib/pgstattuple/sql/pgstattuple.sql
index 0e0ad0e15d5..d22c9f1c46d 100644
--- a/contrib/pgstattuple/sql/pgstattuple.sql
+++ b/contrib/pgstattuple/sql/pgstattuple.sql
@@ -15,12 +15,26 @@ select * from pgstattuple('test'::regclass);
 select pgstattuple(oid) from pg_class where relname = 'test';
 select pgstattuple(relname) from pg_class where relname = 'test';
 
-select * from pgstatindex('test_pkey');
-select * from pgstatindex('test_pkey'::text);
-select * from pgstatindex('test_pkey'::name);
-select * from pgstatindex('test_pkey'::regclass);
-select pgstatindex(oid) from pg_class where relname = 'test_pkey';
-select pgstatindex(relname) from pg_class where relname = 'test_pkey';
+select version, tree_level,
+    index_size / current_setting('block_size')::int as index_size,
+    root_block_no, internal_pages, leaf_pages, empty_pages, deleted_pages,
+    avg_leaf_density, leaf_fragmentation
+    from pgstatindex('test_pkey');
+select version, tree_level,
+    index_size / current_setting('block_size')::int as index_size,
+    root_block_no, internal_pages, leaf_pages, empty_pages, deleted_pages,
+    avg_leaf_density, leaf_fragmentation
+    from pgstatindex('test_pkey'::text);
+select version, tree_level,
+    index_size / current_setting('block_size')::int as index_size,
+    root_block_no, internal_pages, leaf_pages, empty_pages, deleted_pages,
+    avg_leaf_density, leaf_fragmentation
+    from pgstatindex('test_pkey'::name);
+select version, tree_level,
+    index_size / current_setting('block_size')::int as index_size,
+    root_block_no, internal_pages, leaf_pages, empty_pages, deleted_pages,
+    avg_leaf_density, leaf_fragmentation
+    from pgstatindex('test_pkey'::regclass);
 
 select pg_relpages('test');
 select pg_relpages('test_pkey');