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Code review for contrib/pg_freespacemap. Add a storedpages column to
pg_freespacemap_relations --- while one could theoretically get that number by counting rows in pg_freespacemap_pages, it's surely the hard way to do it. Avoid expensive and inconvenient conversion to and from text format. Minor code and docs cleanup.
This commit is contained in:
Tom Lane
@ -39,13 +39,15 @@ Notes
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Column | references | Description
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----------------+----------------------+------------------------------------
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reltablespace | pg_tablespace.oid | Tablespace oid of the relation.
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reldatabase | pg_database.oid | Database for the relation.
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relfilenode | pg_class.relfilenode | Refilenode of the relation.
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reldatabase | pg_database.oid | Database oid of the relation.
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relfilenode | pg_class.relfilenode | Relfilenode of the relation.
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avgrequest | | Moving average of free space
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| | requests.
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lastpagecount | | Count of pages examined for useful
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| | free space.
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nextpage | | page index (from 0) to start next
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| | requests (NULL for indexes)
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lastpagecount | | Count of pages last reported as
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| | containing useful free space.
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storedpages | | Count of pages actually stored
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| | in free space map.
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nextpage | | Page index (from 0) to start next
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| | search at.
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@ -54,24 +56,33 @@ Notes
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Column | references | Description
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----------------+----------------------+------------------------------------
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reltablespace | pg_tablespace.oid | Tablespace oid of the relation.
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reldatabase | pg_database.oid | Database for the relation.
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relfilenode | pg_class.relfilenode | Refilenode of the relation.
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relblocknumber | | Page offset in the relation.
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reldatabase | pg_database.oid | Database oid of the relation.
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relfilenode | pg_class.relfilenode | Relfilenode of the relation.
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relblocknumber | | Page number in the relation.
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bytes | | Free bytes in the page, or NULL
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| | for an index page (see below).
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For pg_freespacemap_relations, there is one row for each relation in the free
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space map.
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space map. storedpages is the number of pages actually stored in the map,
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while lastpagecount is the number of pages VACUUM last tried to store
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(ie, the number that VACUUM thought had useful amounts of free space).
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If storedpages is consistently less than lastpagecount then it'd be a good
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idea to increase max_fsm_pages. Also, if the number of rows in
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pg_freespacemap_relations is close to max_fsm_relations, then you should
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consider increasing max_fsm_relations.
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For pg_freespacemap_pages, there is one row for each page in the free space
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map.
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map. The number of rows for a relation will match the storedpages column
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in pg_freespacemap_relations.
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Because the map is shared by all the databases, there are relations and pages
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from relations not belonging to the current database.
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For indexes, what is tracked is entirely-unused pages, rather than free
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space within pages. Therefore, the average request size and free bytes
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within a page are not meaningful, and are shown as NULL.
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The view 'freespacemap_pages' can contain pages for btree indexes if they
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were emptied by a vacuum process. The bytes field is set to NULL in this case.
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Because the map is shared by all the databases, it will include relations
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not belonging to the current database.
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When either of the views are accessed, internal free space map locks are
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taken, and a copy of the map data is made for them to display.
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@ -85,44 +96,43 @@ Sample output - pg_freespacemap_relations
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regression=# \d pg_freespacemap_relations
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View "public.pg_freespacemap_relations"
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Column | Type | Modifiers
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Column | Type | Modifiers
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---------------+---------+-----------
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reltablespace | oid |
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reldatabase | oid |
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relfilenode | oid |
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avgrequest | bigint |
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lastpagecount | integer |
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nextpage | integer |
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reltablespace | oid |
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reldatabase | oid |
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relfilenode | oid |
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avgrequest | integer |
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lastpagecount | integer |
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storedpages | integer |
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nextpage | integer |
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View definition:
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SELECT p.reltablespace, p.reldatabase, p.relfilenode, p.avgrequest, p.lastpagecount, p.nextpage
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FROM pg_freespacemap_relations() p(reltablespace oid, reldatabase oid, relfilenode oid, avgrequest bigint, lastpagecount integer, nextpage integer);
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SELECT p.reltablespace, p.reldatabase, p.relfilenode, p.avgrequest, p.lastpagecount, p.storedpages, p.nextpage
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FROM pg_freespacemap_relations() p(reltablespace oid, reldatabase oid, relfilenode oid, avgrequest integer, lastpagecount integer, storedpages integer, nextpage integer);
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regression=# SELECT c.relname, r.avgrequest, r.lastpagecount, r.nextpage
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regression=# SELECT c.relname, r.avgrequest, r.lastpagecount, r.storedpages
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FROM pg_freespacemap_relations r INNER JOIN pg_class c
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ON c.relfilenode = r.relfilenode INNER JOIN pg_database d
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ON r.reldatabase = d.oid AND (d.datname = current_database())
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ORDER BY c.relname LIMIT 10;
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relname | avgrequest | lastpagecount | nextpage
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--------------+------------+---------------+----------
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a_star | 250 | 1 | 0
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abstime_tbl | 249 | 1 | 0
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aggtest | 250 | 1 | 0
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altinhoid | 250 | 1 | 0
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altstartwith | 250 | 1 | 0
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arrtest | 254 | 1 | 0
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b_star | 250 | 1 | 0
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box_tbl | 250 | 1 | 0
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bt_f8_heap | 92 | 1 | 0
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bt_i4_heap | 94 | 1 | 0
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ORDER BY r.storedpages DESC LIMIT 10;
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relname | avgrequest | lastpagecount | storedpages
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---------------------------------+------------+---------------+-------------
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onek | 256 | 109 | 109
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pg_attribute | 167 | 93 | 93
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pg_class | 191 | 49 | 49
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pg_attribute_relid_attnam_index | | 48 | 48
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onek2 | 256 | 37 | 37
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pg_depend | 95 | 26 | 26
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pg_type | 199 | 16 | 16
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pg_rewrite | 1011 | 13 | 13
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pg_class_relname_nsp_index | | 10 | 10
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pg_proc | 302 | 8 | 8
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(10 rows)
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regression=#
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Sample output - pg_freespacemap_pages
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-------------
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regression=# \d pg_freespacemap_pages;
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regression=# \d pg_freespacemap_pages
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View "public.pg_freespacemap_pages"
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Column | Type | Modifiers
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----------------+---------+-----------
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@ -154,8 +164,6 @@ regression=# SELECT c.relname, p.relblocknumber, p.bytes
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bt_i4_heap | 49 | 8008
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(10 rows)
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regression=#
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Author
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