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
-
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 ...
-
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 ...
