PostgreSQL的区域设置

对于中文用户，在PostgreSQL中应该将编码无条件的设为UTF8，为简化和统一区域(loacle)也推荐尽量设置为C，但Collate和Ctype对性能或功能有一定影响，需要注意。

环境

• rhel 6.3 x64虚机(4C/8G/300G HDD)
• PostgreSQL 9.6.2

数据库

en_US=# \l+
                                                                   List of databases
   Name    |  Owner   | Encoding |  Collate   |   Ctype    |   Access privileges   |  Size   | Tablespace |                Description                 
-----------+----------+----------+------------+------------+-----------------------+---------+------------+--------------------------------------------
 en_US     | postgres | UTF8     | en_US.UTF8 | en_US.UTF8 |                       | 7343 kB | pg_default | 
 postgres  | postgres | UTF8     | C          | C          |                       | 414 MB  | pg_default | default administrative connection database
 template0 | postgres | UTF8     | C          | C          | =c/postgres          +| 7225 kB | pg_default | unmodifiable empty database
           |          |          |            |            | postgres=CTc/postgres |         |            | 
 template1 | postgres | UTF8     | C          | C          | =c/postgres          +| 7225 kB | pg_default | default template for new databases
           |          |          |            |            | postgres=CTc/postgres |         |            | 
 zh_CN     | postgres | UTF8     | zh_CN.UTF8 | zh_CN.UTF8 |                       | 7225 kB | pg_default | 
(5 rows) 

Collate对功能的影响

Collate会影响中文的排序，在zh_CN的区域下中文按拼音排序，其它区域按字符编码排序。

postgres=# select * from (values ('王'),('貂'),('西'),('杨')) a order by a;
 column1 
---------
 杨
 王
 西
 貂
(4 rows)

postgres=# \c en_US
You are now connected to database "en_US" as user "postgres".
en_US=# select * from (values ('王'),('貂'),('西'),('杨')) a order by a;
 column1 
---------
 杨
 王
 西
 貂
(4 rows)

en_US=# \c zh_CN
You are now connected to database "zh_CN" as user "postgres".
zh_CN=# select * from (values ('王'),('貂'),('西'),('杨')) a order by a;
 column1 
---------
 貂
 王
 西
 杨
(4 rows) 

Collate对性能的影响

测试方法

postgres=# create table tb1(c1 text);
CREATE TABLE
Time: 5.653 ms
postgres=# insert into tb1 select md5(generate_series(1,1000000)::text);
INSERT 0 1000000
Time: 2671.929 ms
postgres=# vacuum ANALYZE tb1;
VACUUM
Time: 398.817 ms
postgres=# select * from tb1 order by c1 limit 1;
                c1                
----------------------------------
 0000104cd168386a335ba6bf6e32219d
(1 row)

Time: 176.779 ms
postgres=# create index idx1 on tb1(c1);
CREATE INDEX
Time: 1549.436 ms 

测试结果

Collate/Ctype       C       en_US.UTF8  zh_CN.UTF8
insert              2671    2613        2670
vacuum ANALYZE      398     250         396
order by            176     388         401
create index        1549    7492        7904
insert(with index)  11199   15621       16128 

Ctype的影响

Ctype会影响pg_trgm和部分正则匹配的结果，比如Ctype为'C'时，pg_trgm将无法支持中文

postgres=# select show_trgm('aaabbbc到的x');
                      show_trgm                      
-----------------------------------------------------
 {"  a","  x"," aa"," x ",aaa,aab,abb,bbb,bbc,"bc "}
(1 row)

en_US=# select show_trgm('aaabbbc到的x');
                               show_trgm                               
-----------------------------------------------------------------------
 {"  a"," aa",0x27bdf1,0x30bd19,0x4624bc,aaa,aab,abb,bbb,bbc,0x6a2ad5}
(1 row)

zh_CN=# select show_trgm('aaabbbc到的x');
                               show_trgm                               
-----------------------------------------------------------------------
 {"  a"," aa",0x27bdf1,0x30bd19,0x4624bc,aaa,aab,abb,bbb,bbc,0x6a2ad5}
(1 row) 

结论

1. 对性能要求不高的场景建议将Collate和Ctype都设置为zh_CN.UTF8，其它区域设置为C。

   initdb -E UTF8 --locale=C --lc-collate=zh_CN.UTF8 --lc-ctype=zh_CN.UTF8 ... 

2. 对性能要求较高的场景建议将Ctype设置为zh_CN.UTF8，其它区域设置为C。如果有部分查询需要按拼音排序，可在列定义和SQL表达式中指定Collate为zh_CN。

   initdb -E UTF8 --locale=C --lc-ctype=zh_CN.UTF8 ... 

参考

• PostgreSQL中的区域和编码