From 0f359c7de9f5f8fceedfebfae0b0cbbf01d1f5bf Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Thu, 18 Feb 2016 15:40:36 -0500 Subject: [PATCH] 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. --- contrib/pgstattuple/pgstatindex.c | 16 ++++++---------- doc/src/sgml/pgstattuple.sgml | 15 +++++++++++---- 2 files changed, 17 insertions(+), 14 deletions(-) diff --git a/contrib/pgstattuple/pgstatindex.c b/contrib/pgstattuple/pgstatindex.c index ceabd862a86..0aa517a870a 100644 --- a/contrib/pgstattuple/pgstatindex.c +++ b/contrib/pgstattuple/pgstatindex.c @@ -66,7 +66,6 @@ typedef struct BTIndexStat uint32 level; BlockNumber root_blkno; - uint64 root_pages; uint64 internal_pages; uint64 leaf_pages; uint64 empty_pages; @@ -133,7 +132,6 @@ pgstatindex(PG_FUNCTION_ARGS) } /* -- init counters -- */ - indexStat.root_pages = 0; indexStat.internal_pages = 0; indexStat.leaf_pages = 0; indexStat.empty_pages = 0; @@ -166,7 +164,11 @@ 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; @@ -183,12 +185,6 @@ 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++; @@ -220,7 +216,7 @@ 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 + diff --git a/doc/src/sgml/pgstattuple.sgml b/doc/src/sgml/pgstattuple.sgml index a55b35cb3f1..7f1ae8d3048 100644 --- a/doc/src/sgml/pgstattuple.sgml +++ b/doc/src/sgml/pgstattuple.sgml @@ -146,13 +146,13 @@ 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 @@ -186,13 +186,13 @@ leaf_fragmentation | 0 index_size bigint - Total number of pages in index + Total index size in bytes root_block_no bigint - Location of root block + Location of root page (zero if none) @@ -236,6 +236,13 @@ leaf_fragmentation | 0 + + The reported index_size will normally correspond to one more + page than is accounted for by internal_pages + leaf_pages + + empty_pages + deleted_pages, because it also includes the + index's metapage. + + As with pgstattuple, the results are accumulated page-by-page, and should not be expected to represent an