Location via proxy:   [ UP ]  
[Report a bug]   [Manage cookies]                
Skip to content

Commit a43974c

Browse files
tglsfdctglsfdc
committed
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.
1 parent 46287bd commit a43974c

File tree

3 files changed

+181
-211
lines changed

3 files changed

+181
-211
lines changed

‎contrib/pg_freespacemap/README.pg_freespacemap

Lines changed: 51 additions & 43 deletions
Original file line numberDiff line numberDiff line change
@@ -39,13 +39,15 @@ Notes
3939
Column | references | Description
4040
----------------+----------------------+------------------------------------
4141
reltablespace | pg_tablespace.oid | Tablespace oid of the relation.
42-
reldatabase | pg_database.oid | Database for the relation.
43-
relfilenode | pg_class.relfilenode | Refilenode of the relation.
42+
reldatabase | pg_database.oid | Database oid of the relation.
43+
relfilenode | pg_class.relfilenode | Relfilenode of the relation.
4444
avgrequest | | Moving average of free space
45-
| | requests.
46-
lastpagecount | | Count of pages examined for useful
47-
| | free space.
48-
nextpage | | page index (from 0) to start next
45+
| | requests (NULL for indexes)
46+
lastpagecount | | Count of pages last reported as
47+
| | containing useful free space.
48+
storedpages | | Count of pages actually stored
49+
| | in free space map.
50+
nextpage | | Page index (from 0) to start next
4951
| | search at.
5052

5153

@@ -54,24 +56,33 @@ Notes
5456
Column | references | Description
5557
----------------+----------------------+------------------------------------
5658
reltablespace | pg_tablespace.oid | Tablespace oid of the relation.
57-
reldatabase | pg_database.oid | Database for the relation.
58-
relfilenode | pg_class.relfilenode | Refilenode of the relation.
59-
relblocknumber | | Page offset in the relation.
59+
reldatabase | pg_database.oid | Database oid of the relation.
60+
relfilenode | pg_class.relfilenode | Relfilenode of the relation.
61+
relblocknumber | | Page number in the relation.
6062
bytes | | Free bytes in the page, or NULL
6163
| | for an index page (see below).
6264

6365

6466
For pg_freespacemap_relations, there is one row for each relation in the free
65-
space map.
67+
space map. storedpages is the number of pages actually stored in the map,
68+
while lastpagecount is the number of pages VACUUM last tried to store
69+
(ie, the number that VACUUM thought had useful amounts of free space).
70+
71+
If storedpages is consistently less than lastpagecount then it'd be a good
72+
idea to increase max_fsm_pages. Also, if the number of rows in
73+
pg_freespacemap_relations is close to max_fsm_relations, then you should
74+
consider increasing max_fsm_relations.
6675

6776
For pg_freespacemap_pages, there is one row for each page in the free space
68-
map.
77+
map. The number of rows for a relation will match the storedpages column
78+
in pg_freespacemap_relations.
6979

70-
Because the map is shared by all the databases, there are relations and pages
71-
from relations not belonging to the current database.
80+
For indexes, what is tracked is entirely-unused pages, rather than free
81+
space within pages. Therefore, the average request size and free bytes
82+
within a page are not meaningful, and are shown as NULL.
7283

73-
The view 'freespacemap_pages' can contain pages for btree indexes if they
74-
were emptied by a vacuum process. The bytes field is set to NULL in this case.
84+
Because the map is shared by all the databases, it will include relations
85+
not belonging to the current database.
7586

7687
When either of the views are accessed, internal free space map locks are
7788
taken, and a copy of the map data is made for them to display.
@@ -85,44 +96,43 @@ Sample output - pg_freespacemap_relations
8596

8697
regression=# \d pg_freespacemap_relations
8798
View "public.pg_freespacemap_relations"
88-
Column | Type | Modifiers
99+
Column | Type | Modifiers
89100
---------------+---------+-----------
90-
reltablespace | oid |
91-
reldatabase | oid |
92-
relfilenode | oid |
93-
avgrequest | bigint |
94-
lastpagecount | integer |
95-
nextpage | integer |
101+
reltablespace | oid |
102+
reldatabase | oid |
103+
relfilenode | oid |
104+
avgrequest | integer |
105+
lastpagecount | integer |
106+
storedpages | integer |
107+
nextpage | integer |
96108
View definition:
97-
SELECT p.reltablespace, p.reldatabase, p.relfilenode, p.avgrequest, p.lastpagecount, p.nextpage
98-
FROM pg_freespacemap_relations() p(reltablespace oid, reldatabase oid, relfilenode oid, avgrequest bigint, lastpagecount integer, nextpage integer);
109+
SELECT p.reltablespace, p.reldatabase, p.relfilenode, p.avgrequest, p.lastpagecount, p.storedpages, p.nextpage
110+
FROM pg_freespacemap_relations() p(reltablespace oid, reldatabase oid, relfilenode oid, avgrequest integer, lastpagecount integer, storedpages integer, nextpage integer);
99111

100-
regression=# SELECT c.relname, r.avgrequest, r.lastpagecount, r.nextpage
112+
regression=# SELECT c.relname, r.avgrequest, r.lastpagecount, r.storedpages
101113
FROM pg_freespacemap_relations r INNER JOIN pg_class c
102114
ON c.relfilenode = r.relfilenode INNER JOIN pg_database d
103115
ON r.reldatabase = d.oid AND (d.datname = current_database())
104-
ORDER BY c.relname LIMIT 10;
105-
relname | avgrequest | lastpagecount | nextpage
106-
--------------+------------+---------------+----------
107-
a_star | 250 | 1 | 0
108-
abstime_tbl | 249 | 1 | 0
109-
aggtest | 250 | 1 | 0
110-
altinhoid | 250 | 1 | 0
111-
altstartwith | 250 | 1 | 0
112-
arrtest | 254 | 1 | 0
113-
b_star | 250 | 1 | 0
114-
box_tbl | 250 | 1 | 0
115-
bt_f8_heap | 92 | 1 | 0
116-
bt_i4_heap | 94 | 1 | 0
116+
ORDER BY r.storedpages DESC LIMIT 10;
117+
relname | avgrequest | lastpagecount | storedpages
118+
---------------------------------+------------+---------------+-------------
119+
onek | 256 | 109 | 109
120+
pg_attribute | 167 | 93 | 93
121+
pg_class | 191 | 49 | 49
122+
pg_attribute_relid_attnam_index | | 48 | 48
123+
onek2 | 256 | 37 | 37
124+
pg_depend | 95 | 26 | 26
125+
pg_type | 199 | 16 | 16
126+
pg_rewrite | 1011 | 13 | 13
127+
pg_class_relname_nsp_index | | 10 | 10
128+
pg_proc | 302 | 8 | 8
117129
(10 rows)
118130

119-
regression=#
120-
121131

122132
Sample output - pg_freespacemap_pages
123133
-------------
124134

125-
regression=# \d pg_freespacemap_pages;
135+
regression=# \d pg_freespacemap_pages
126136
View "public.pg_freespacemap_pages"
127137
Column | Type | Modifiers
128138
----------------+---------+-----------
@@ -154,8 +164,6 @@ regression=# SELECT c.relname, p.relblocknumber, p.bytes
154164
bt_i4_heap | 49 | 8008
155165
(10 rows)
156166

157-
regression=#
158-
159167

160168

161169
Author

0 commit comments

Comments
 (0)