PostgreSQL 8.3beta3 Documentation | ||||
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pgstattuple modules provides various functions to obtain tuple statistics.
pgstattuple() returns the relation length, percentage of the "dead" tuples of a relation and other info. This may help users to determine whether vacuum is necessary or not. Here is an example session:
test=> \x Expanded display is on. test=> SELECT * FROM pgstattuple('pg_catalog.pg_proc'); -[ RECORD 1 ]------+------- table_len | 458752 tuple_count | 1470 tuple_len | 438896 tuple_percent | 95.67 dead_tuple_count | 11 dead_tuple_len | 3157 dead_tuple_percent | 0.69 free_space | 8932 free_percent | 1.95
Here are explanations for each column:
Table F-19. pgstattuple() column descriptions
Column | Description |
---|---|
table_len | physical relation length in bytes |
tuple_count | number of live tuples |
tuple_len | total tuples length in bytes |
tuple_percent | live tuples in % |
dead_tuple_len | total dead tuples length in bytes |
dead_tuple_percent | dead tuples in % |
free_space | free space in bytes |
free_percent | free space in % |
Note: pgstattuple acquires only a read lock on the relation. So concurrent update may affect the result.
Note: pgstattuple judges a tuple is "dead" if HeapTupleSatisfiesNow() returns false.
pg_relpages() returns the number of pages in the relation.
pgstatindex() returns an array showing the information about an index:
test=> \x Expanded display is on. test=> SELECT * FROM pgstatindex('pg_cast_oid_index'); -[ RECORD 1 ]------+------ version | 2 tree_level | 0 index_size | 8192 root_block_no | 1 internal_pages | 0 leaf_pages | 1 empty_pages | 0 deleted_pages | 0 avg_leaf_density | 50.27 leaf_fragmentation | 0
pgstattuple may be called as a relation function and is defined as follows:
CREATE OR REPLACE FUNCTION pgstattuple(text) RETURNS pgstattuple_type AS 'MODULE_PATHNAME', 'pgstattuple' LANGUAGE C STRICT; CREATE OR REPLACE FUNCTION pgstattuple(oid) RETURNS pgstattuple_type AS 'MODULE_PATHNAME', 'pgstattuplebyid' LANGUAGE C STRICT;
The argument is the relation name (optionally it may be qualified) or the OID of the relation. Note that pgstattuple only returns one row.