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我在 Oracle Linux Server 6.3 版上使用 postgresql 9.2.1。

我正在努力获取表和索引的预期存储大小。

感谢这个网站的一些建议，我为下面的表格制作了我的公式......

-- 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。

  • 实际存储中的元组大小：8072（第一次插入后的空闲空间）-7980（第二次插入后的空闲空间）= 92
  • 页面默认值 = 8192 - 8072（第一次插入后的空闲空间） - 92（元组大小）= 28
  • 9182 - 28 = 92 * X（每页的最大元组数）

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)

再次，我发现每个页面可以容纳 135(Y) 个元组。

  • 实际存储中的元组大小：8088（第一次插入后的空闲空间）-8028（第二次插入后的空闲空间）= 60
  • 页面默认值 = 8192 - 8088（第一次插入后的空闲空间） - 60（元组大小）= 44
  • 8192 - 44 = 60 * Y（每页中的最大元组数）

当我在表中插入 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)

表格的文件大小？

1350(行数) / 88(X) = 15.34 --> 这意味着需要 16 页，这意味着文件大小为 16*8192 = 131072。看起来不错。

但是，索引大小不同...

1350（行数）/ 135（Y）= 10 正好...文件大小需要 10*8192，但需要 90112。

再插入 1 行，除此之外，应该扩展 index_size（如果我是对的）所以我尝试了但没有更改。

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)

我什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......

我需要我自己的公式，特别是为了获得预期的索引大小，包括由 TOAST 决定的附加文件......

任何建议将不胜感激。

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1 回答 1

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您在这里遇到的真正问题之一是 varchar 不使用恒定数量的空间。随着时间的推移，这可能会使您的页面估算值下降（您的估算值基本上是最大值，可能会更少）。使用您的表格结构，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，您可以预期您的估计代表一个最大的、未知的准确数量。实际大小将取决于您的实际数据，而不仅仅是架构和行数。

于 2013-04-15T15:21:04.933 回答