我在Oracle Linux Server 6.3版上使用postgresql 9.2.1。
我正在努力获得表和索引的预期存储大小。
感谢本网站提供的一些建议，我为下表制作了我的公式......
- 如果是TABLE ...
postgres=# \d test
Table "public.test"
Column | Type | Modifiers
---------------+-----------------------+-----------
c1 | integer | not null
c2 | character varying(20) | not null
c3 | character varying(8) | not null
c4 | character varying(6) | not null
c5 | character varying(15) |
c6 | character varying(20) |
c7 | character varying(20) |
c8 | character varying(20) |
Indexes:
"idx_test" PRIMARY KEY, btree (c1, c3, c4, c5)
Tablespace: "test"
postgres=# insert into test values(1,
'11111111111111111111', -- 20(exactly same with max length of each column)
'11111111', -- 8
'111111', -- 6
'111111111111111', -- 15
'11111111111111111111', -- 20
'11111111111111111111', -- 20
'11111111111111111111');-- 20
INSERT 0 1
postgres=# select * from pgstattuple('test');
table_len | tuple_count | tuple_len | tuple_percent | dead_tuple_count | dead_tuple_len | dead_tuple_percent | free_space | free_percent
-----------+-------------+-----------+---------------+------------------+----------------+--------------------+------------+--------------
8192 | 1 | 81 | 0.99 | 0 | 0 | 0 | 8072 | 98.54
postgres=# insert into test values(2,
'11111111111111111111', -- 20(exactly same with max length of each column)
'11111111', -- 8
'111111', -- 6
'111111111111111', -- 15
'11111111111111111111', -- 20
'11111111111111111111', -- 20
'11111111111111111111');-- 20
INSERT 0 1
postgres=# select * from pgstattuple('test');
table_len | tuple_count | tuple_len | tuple_percent | dead_tuple_count | dead_tuple_len | dead_tuple_percent | free_space | free_percent
-----------+-------------+-----------+---------------+------------------+----------------+--------------------+------------+--------------
8192 | 2 | 162 | 1.98 | 0 | 0 | 0 | 7980 | 97.41
所以，我发现每个页面可以容纳88（X）个元组。
如果是索引...
postgres=# \d test_pkey
Index "public.idx_test"
Column | Type | Definition
---------------+-----------------------+---------------
c1 | integer | c1
c2 | character varying(20) | c2
c3 | character varying(8) | c3
c4 | character varying(6) | c4
primary key, btree, for table "public.test"
postgres=# truncate table test;
postgres=# vacuum;
postgres=# analyze;
postgres=# insert into test values(1,
'11111111111111111111', -- 20(exactly same with max length of each column)
'11111111', -- 8
'111111', -- 6
'111111111111111', -- 15
'11111111111111111111', -- 20
'11111111111111111111', -- 20
'11111111111111111111');-- 20
INSERT 0 1
postgres=# select * from pgstattuple('idx_test');
table_len | tuple_count | tuple_len | tuple_percent | dead_tuple_count | dead_tuple_len | dead_tuple_percent | free_space | free_percent
-----------+-------------+-----------+---------------+------------------+----------------+--------------------+------------+--------------
16384 | 1 | 56 | 0.34 | 0 | 0 | 0 | 8088 | 49.37
(1 row)
postgres=# select * from pgstatindex('idx_test');
version | tree_level | index_size | root_block_no | internal_pages | leaf_pages | empty_pages | deleted_pages | avg_leaf_density | leaf_fragmentation
---------+------------+------------+---------------+----------------+------------+-------------+---------------+------------------+--------------------
2 | 0 | 8192 | 1 | 0 | 1 | 0 | 0 | 0.79 | 0
(1 row)
postgres=# insert into test values(1,
'11111111111111111111', -- 20(exactly same with max length of each column)
'11111111', -- 8
'111111', -- 6
'111111111111111', -- 15
'11111111111111111111', -- 20
'11111111111111111111', -- 20
'11111111111111111111');-- 20
INSERT 0 1
postgres=# select * from pgstattuple('idx_test');
table_len | tuple_count | tuple_len | tuple_percent | dead_tuple_count | dead_tuple_len | dead_tuple_percent | free_space | free_percent
-----------+-------------+-----------+---------------+------------------+----------------+--------------------+------------+--------------
16384 | 2 | 112 | 0.68 | 0 | 0 | 0 | 8028 | 49
(1 row)
postgres=# select * from pgstatindex('idx_test');
version | tree_level | index_size | root_block_no | internal_pages | leaf_pages | empty_pages | deleted_pages | avg_leaf_density | leaf_fragmentation
---------+------------+------------+---------------+----------------+------------+-------------+---------------+------------------+--------------------
2 | 0 | 8192 | 1 | 0 | 1 | 0 | 0 | 1.52 | 0
(1 row)
同样，我发现每个页面可以容纳135（Y）个元组。
当我在表格中插入1350行时......我得到了这个......
postgres=# select * from pgstattuple('test');
table_len | tuple_count | tuple_len | tuple_percent | dead_tuple_count | dead_tuple_len | dead_tuple_percent | free_space | free_percent
-----------+-------------+-----------+---------------+------------------+----------------+--------------------+------------+--------------
131072 | 1350 | 109350 | 83.43 | 0 | 0 | 0 | 6424 | 4.9
(1 row)
postgres=# select * from pgstattuple('idx_test');
table_len | tuple_count | tuple_len | tuple_percent | dead_tuple_count | dead_tuple_len | dead_tuple_percent | free_space | free_percent
-----------+-------------+-----------+---------------+------------------+----------------+--------------------+------------+--------------
90112 | 1350 | 54000 | 59.93 | 0 | 0 | 0 | 13580 | 15.07
(1 row)
postgres=# select * from pgstatindex('idx_test');
version | tree_level | index_size | root_block_no | internal_pages | leaf_pages | empty_pages | deleted_pages | avg_leaf_density | leaf_fragmentation
---------+------------+------------+---------------+----------------+------------+-------------+---------------+------------------+--------------------
2 | 1 | 81920 | 3 | 0 | 9 | 0 | 0 | 81.49 | 0
(1 row)
表的文件大小？
1350（行数）/ 88（X）= 15.34 - ＆gt;这意味着需要16页，这意味着文件大小为16 * 8192 = 131072.看起来是正确的。
然而，索引是不同的......
1350（行数）/ 135（Y）= 10正好... 10 * 8192需要文件大小但是90112。
再插入一行，除此之外，应该扩展index_size（如果我是对的）所以我尝试但没有更改。
postgres=# insert into test values(27108,'sanjuk1052','20121022','233338','172,20,30,177','win7','IE','9,0');
INSERT 0 1
postgres=# select * from pgstattuple('test');
table_len | tuple_count | tuple_len | tuple_percent | dead_tuple_count | dead_tuple_len | dead_tuple_percent | free_space | free_percent
-----------+-------------+-----------+---------------+------------------+----------------+--------------------+------------+--------------
131072 | 1351 | 109431 | 83.49 | 0 | 0 | 0 | 6332 | 4.83
(1 row)
postgres=# select * from pgstattuple('idx_test');
table_len | tuple_count | tuple_len | tuple_percent | dead_tuple_count | dead_tuple_len | dead_tuple_percent | free_space | free_percent
-----------+-------------+-----------+---------------+------------------+----------------+--------------------+------------+--------------
90112 | 1351 | 54040 | 59.97 | 0 | 0 | 0 | 13536 | 15.02
(1 row)
postgres=# select * from pgstatindex('idx_test');
version | tree_level | index_size | root_block_no | internal_pages | leaf_pages | empty_pages | deleted_pages | avg_leaf_density | leaf_fragmentation
---------+------------+------------+---------------+----------------+------------+-------------+---------------+------------------+--------------------
2 | 1 | 81920 | 3 | 0 | 9 | 0 | 0 | 81.55 | 0
(1 row)
我甚至不能确定这种方法是否合理，但即使不完美，也必须完成工作...
我需要自己的公式，特别是要获得预期的索引大小，包括由TOAST重新调整的其他文件...
非常感谢任何建议。
答案 0 :(得分：0)
您在这里遇到的一个真正问题是varchar不使用恒定的空间量。这可能会导致您的页面估算值随时间推移（您的估算值基本上是最大值，可能会更低）。凭借你的桌子结构，我认为任何东西都不会被烘烤。
这也会影响您的索引，因为您有可变长度字段。因此，您可以预期您的估算值代表最大值，而不是已知的准确值。实际大小取决于您的实际数据，而不仅仅是架构和行数。