| Postgres-XC 1.1 Documentation | ||||
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The pgstattuple module provides various functions to obtain tuple-level statistics.
Note: The following description applies only to Postgres-XC
Functions of this module returns information about connecting Coordinators locally. To get information of a Datanode, you can connect to the Datanode using psql directly.
pgstattuple(text) returns record pgstattuple returns a relation's physical length,
percentage of "dead" tuples, and other info. This may help users
to determine whether vacuum is necessary or not. The argument is the
target relation's name (optionally schema-qualified).
For example:
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 | 1.95The output columns are described in Table F-20.
Table F-20. pgstattuple Output Columns
| Column | Type | Description |
|---|---|---|
| table_len | bigint | Physical relation length in bytes |
| tuple_count | bigint | Number of live tuples |
| tuple_len | bigint | Total length of live tuples in bytes |
| tuple_percent | float8 | Percentage of live tuples |
| dead_tuple_count | bigint | Number of dead tuples |
| dead_tuple_len | bigint | Total length of dead tuples in bytes |
| dead_tuple_percent | float8 | Percentage of dead tuples |
| free_space | bigint | Total free space in bytes |
| free_percent | float8 | Percentage of free space |
pgstattuple acquires only a read lock on the
relation. So the results do not reflect an instantaneous snapshot;
concurrent updates will affect them.
pgstattuple judges a tuple is "dead" if
HeapTupleSatisfiesNow returns false.
pgstattuple(oid) returns record This is the same as pgstattuple(text), except
that the target relation is specified by OID.
pgstatindex(text) returns record pgstatindex returns a record showing information
about a B-tree index. For example:
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
The output columns are:
| Column | Type | Description |
|---|---|---|
| version | integer | B-tree version number |
| tree_level | integer | Tree level of the root page |
| index_size | bigint | Total number of pages in index |
| root_block_no | bigint | Location of root block |
| internal_pages | bigint | Number of "internal" (upper-level) pages |
| leaf_pages | bigint | Number of leaf pages |
| empty_pages | bigint | Number of empty pages |
| deleted_pages | bigint | Number of deleted pages |
| avg_leaf_density | float8 | Average density of leaf pages |
| leaf_fragmentation | float8 | Leaf page fragmentation |
As with pgstattuple, the results are accumulated
page-by-page, and should not be expected to represent an
instantaneous snapshot of the whole index.
pg_relpages(text) returns bigint pg_relpages returns the number of pages in the
relation.
Tatsuo Ishii and Satoshi Nagayasu