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.

1 files changed, 20 insertions, 6 deletions

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');