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Add functions to /contrib/pgstattuple that show index statistics and
index page contents. Satoshi Nagayasu
This commit is contained in:
Bruce Momjian
@@ -1,36 +1,108 @@
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pgstattuple README 2002/08/29 Tatsuo Ishii
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1. What is pgstattuple?
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1. Functions supported:
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pgstattuple returns the relation length, percentage of the "dead"
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tuples of a relation and other info. This may help users to determine
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whether vacuum is necessary or not. Here is an example session:
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pgstattuple
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-----------
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pgstattuple() returns the relation length, percentage of the "dead"
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tuples of a relation and other info. This may help users to determine
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whether vacuum is necessary or not. Here is an example session:
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test=# \x
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Expanded display is on.
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test=# select * from pgstattuple('pg_catalog.pg_proc');
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-[ RECORD 1 ]------+-------
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table_len | 458752
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tuple_count | 1470
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tuple_len | 438896
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tuple_percent | 95.67
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dead_tuple_count | 11
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dead_tuple_len | 3157
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dead_tuple_percent | 0.69
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free_space | 8932
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free_percent | 1.95
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test=> \x
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Expanded display is on.
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test=> SELECT * FROM pgstattuple('pg_catalog.pg_proc');
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-[ RECORD 1 ]------+-------
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table_len | 458752
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tuple_count | 1470
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tuple_len | 438896
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tuple_percent | 95.67
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dead_tuple_count | 11
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dead_tuple_len | 3157
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dead_tuple_percent | 0.69
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free_space | 8932
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free_percent | 1.95
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Here are explanations for each column:
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Here are explanations for each column:
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table_len -- physical relation length in bytes
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tuple_count -- number of live tuples
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tuple_len -- total tuples length in bytes
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tuple_percent -- live tuples in %
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dead_tuple_len -- total dead tuples length in bytes
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dead_tuple_percent -- dead tuples in %
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free_space -- free space in bytes
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free_percent -- free space in %
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pg_relpages
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-----------
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pg_relpages() returns the number of pages in the relation.
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pgstatindex
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-----------
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pgstatindex() returns an array showing the information about an index:
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test=> \x
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Expanded display is on.
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test=> SELECT * FROM pgstatindex('pg_cast_oid_index');
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-[ RECORD 1 ]------+------
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version | 2
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tree_level | 0
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index_size | 8192
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root_block_no | 1
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internal_pages | 0
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leaf_pages | 1
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empty_pages | 0
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deleted_pages | 0
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avg_leaf_density | 50.27
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leaf_fragmentation | 0
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bt_metap
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--------
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bt_metap() returns information about the btree index metapage:
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test=> SELECT * FROM bt_metap('pg_cast_oid_index');
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-[ RECORD 1 ]-----
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magic | 340322
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version | 2
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root | 1
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level | 0
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fastroot | 1
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fastlevel | 0
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bt_page_stats
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-------------
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bt_page_stats() shows information about single btree pages:
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test=> SELECT * FROM bt_page_stats('pg_cast_oid_index', 1);
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-[ RECORD 1 ]-+-----
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blkno | 1
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type | l
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live_items | 256
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dead_items | 0
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avg_item_size | 12
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page_size | 8192
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free_size | 4056
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btpo_prev | 0
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btpo_next | 0
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btpo | 0
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btpo_flags | 3
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bt_page_items
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-------------
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bt_page_items() returns information about specific items on btree pages:
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test=> SELECT * FROM bt_page_items('pg_cast_oid_index', 1);
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itemoffset | ctid | itemlen | nulls | vars | data
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------------+---------+---------+-------+------+-------------
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1 | (0,1) | 12 | f | f | 23 27 00 00
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2 | (0,2) | 12 | f | f | 24 27 00 00
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3 | (0,3) | 12 | f | f | 25 27 00 00
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4 | (0,4) | 12 | f | f | 26 27 00 00
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5 | (0,5) | 12 | f | f | 27 27 00 00
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6 | (0,6) | 12 | f | f | 28 27 00 00
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7 | (0,7) | 12 | f | f | 29 27 00 00
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8 | (0,8) | 12 | f | f | 2a 27 00 00
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table_len -- physical relation length in bytes
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tuple_count -- number of live tuples
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tuple_len -- total tuples length in bytes
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tuple_percent -- live tuples in %
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dead_tuple_len -- total dead tuples length in bytes
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dead_tuple_percent -- dead tuples in %
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free_space -- free space in bytes
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free_percent -- free space in %
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2. Installing pgstattuple
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@@ -38,33 +110,36 @@ free_percent -- free space in %
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$ make install
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$ psql -e -f /usr/local/pgsql/share/contrib/pgstattuple.sql test
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3. Using pgstattuple
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pgstattuple may be called as a relation function and is
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defined as follows:
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pgstattuple may be called as a relation function and is
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defined as follows:
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CREATE OR REPLACE FUNCTION pgstattuple(text) RETURNS pgstattuple_type
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CREATE OR REPLACE FUNCTION pgstattuple(text) RETURNS pgstattuple_type
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AS 'MODULE_PATHNAME', 'pgstattuple'
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LANGUAGE C STRICT;
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CREATE OR REPLACE FUNCTION pgstattuple(oid) RETURNS pgstattuple_type
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CREATE OR REPLACE FUNCTION pgstattuple(oid) RETURNS pgstattuple_type
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AS 'MODULE_PATHNAME', 'pgstattuplebyid'
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LANGUAGE C STRICT;
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The argument is the relation name (optionally it may be qualified)
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or the OID of the relation. Note that pgstattuple only returns
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one row.
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The argument is the relation name (optionally it may be qualified)
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or the OID of the relation. Note that pgstattuple only returns
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one row.
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4. Notes
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pgstattuple acquires only a read lock on the relation. So concurrent
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update may affect the result.
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pgstattuple acquires only a read lock on the relation. So concurrent
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update may affect the result.
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pgstattuple judges a tuple is "dead" if HeapTupleSatisfiesNow()
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returns false.
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pgstattuple judges a tuple is "dead" if HeapTupleSatisfiesNow()
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returns false.
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5. History
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2006/06/28
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2006/06/28
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Extended to work against indexes.
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