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

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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 d287818eb5.

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.
This commit is contained in:
Tom Lane 2016-02-18 15:40:35 -05:00
parent b3ec98c8bd
commit 9dfb5b9407
4 changed files with 28 additions and 17 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
contrib/pgstattuple/expected/pgstattuple.out
View File

@ -17,10 +17,14 @@ select * from pgstattuple('test'::regclass);
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 pg_relpages('test');

16
contrib/pgstattuple/pgstatindex.c
View File

@ -72,7 +72,6 @@ typedef struct BTIndexStat
uint32 level;
BlockNumber root_blkno;
uint64 root_pages;
uint64 internal_pages;
uint64 leaf_pages;
uint64 empty_pages;
@ -153,7 +152,6 @@ pgstatindex(PG_FUNCTION_ARGS)
}
/* -- init counters -- */
indexStat.root_pages = 0;
indexStat.internal_pages = 0;
indexStat.leaf_pages = 0;
indexStat.empty_pages = 0;
@ -186,7 +184,11 @@ pgstatindex(PG_FUNCTION_ARGS)
/* 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;
@ -203,12 +205,6 @@ pgstatindex(PG_FUNCTION_ARGS)
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++;
@ -240,7 +236,7 @@ pgstatindex(PG_FUNCTION_ARGS)
snprintf(values[j++], 32, "%d", indexStat.level);
values[j] = palloc(32);
snprintf(values[j++], 32, INT64_FORMAT,
(indexStat.root_pages +
(1 + /* include the metapage in index_size */
indexStat.leaf_pages +
indexStat.internal_pages +
indexStat.deleted_pages +

6
contrib/pgstattuple/sql/pgstattuple.sql
View File

@ -11,7 +11,11 @@ create table test (a int primary key, b int[]);
select * from pgstattuple('test'::text);
select * from pgstattuple('test'::regclass);
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');
select pg_relpages('test');
select pg_relpages('test_pkey');

15
doc/src/sgml/pgstattuple.sgml
View File

@ -153,13 +153,13 @@ test=> SELECT * FROM pgstatindex('pg_cast_oid_index');
-[ RECORD 1 ]------+------
version | 2
tree_level | 0
index_size | 8192
index_size | 16384
root_block_no | 1
internal_pages | 0
leaf_pages | 1
empty_pages | 0
deleted_pages | 0
avg_leaf_density | 50.27
avg_leaf_density | 54.27
leaf_fragmentation | 0
</programlisting>
</para>
@ -193,13 +193,13 @@ leaf_fragmentation | 0
<row>
<entry><structfield>index_size</structfield></entry>
<entry><type>bigint</type></entry>
<entry>Total number of pages in index</entry>
<entry>Total index size in bytes</entry>
</row>
<row>
<entry><structfield>root_block_no</structfield></entry>
<entry><type>bigint</type></entry>
<entry>Location of root block</entry>
<entry>Location of root page (zero if none)</entry>
</row>
<row>
@ -243,6 +243,13 @@ leaf_fragmentation | 0
</informaltable>
</para>
<para>
The reported <literal>index_size</> will normally correspond to one more
page than is accounted for by <literal>internal_pages + leaf_pages +
empty_pages + deleted_pages</literal>, because it also includes the
index's metapage.
</para>
<para>
As with <function>pgstattuple</>, the results are accumulated
page-by-page, and should not be expected to represent an