readme.pgstattuple

来自「PostgreSQL 8.2中增加了很多企业用户所需要的功能和性能上的提高,其开」· PGSTATTUPLE 代码 · 共 146 行

pgstattuple README			2002/08/29 Tatsuo Ishii

1. Functions supported:

    pgstattuple
    -----------
    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_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 %

    pg_relpages
    -----------
    pg_relpages() returns the number of pages in the relation.

    pgstatindex
    -----------
    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

    bt_metap
    --------
    bt_metap() returns information about the btree index metapage:

        test=> SELECT * FROM bt_metap('pg_cast_oid_index');
        -[ RECORD 1 ]-----
        magic     | 340322
        version   | 2
        root      | 1
        level     | 0
        fastroot  | 1
        fastlevel | 0

    bt_page_stats
    -------------
    bt_page_stats() shows information about single btree pages:

        test=> SELECT * FROM bt_page_stats('pg_cast_oid_index', 1);
        -[ RECORD 1 ]-+-----
        blkno         | 1
        type          | l
        live_items    | 256
        dead_items    | 0
        avg_item_size | 12
        page_size     | 8192
        free_size     | 4056
        btpo_prev     | 0
        btpo_next     | 0
        btpo          | 0
        btpo_flags    | 3

    bt_page_items
    -------------
    bt_page_items() returns information about specific items on btree pages:

        test=> SELECT * FROM bt_page_items('pg_cast_oid_index', 1);
         itemoffset |  ctid   | itemlen | nulls | vars |    data
        ------------+---------+---------+-------+------+-------------
                  1 | (0,1)   |      12 | f     | f    | 23 27 00 00
                  2 | (0,2)   |      12 | f     | f    | 24 27 00 00
                  3 | (0,3)   |      12 | f     | f    | 25 27 00 00
                  4 | (0,4)   |      12 | f     | f    | 26 27 00 00
                  5 | (0,5)   |      12 | f     | f    | 27 27 00 00
                  6 | (0,6)   |      12 | f     | f    | 28 27 00 00
                  7 | (0,7)   |      12 | f     | f    | 29 27 00 00
                  8 | (0,8)   |      12 | f     | f    | 2a 27 00 00


2. Installing pgstattuple

    $ make
    $ make install
    $ psql -e -f /usr/local/pgsql/share/contrib/pgstattuple.sql test


3. Using pgstattuple

    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.


4. Notes

    pgstattuple acquires only a read lock on the relation. So concurrent
    update may affect the result.

    pgstattuple judges a tuple is "dead" if HeapTupleSatisfiesNow()
    returns false.


5. History

    2006/06/28

	Extended to work against indexes.