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PostgreSQL 最佳实践 - 水平分库(基于plproxy)

作者

digoal

日期

2016-08-24

标签

PostgreSQL , plproxy , 水平分库


背景

我一直以来都比较推荐plproxy这个PostgreSQL代理软件, 因为它小巧灵活好用, 效率高.

最近朋友邀请我给他们做个分布式的方案, 所以又把plproxy翻出来了.

本文讲一讲在单节点中如何快速的部署plproxy环境.

环境

PostgreSQL 9.3.1    
plproxy 2.x    

plrpoxy节点

hostaddr 172.16.3.150    
port 1921    
user proxy    
password proxy    
dbname proxy    
schema digoal  // 这个schema名和数据节点一致, 可以省去写plproxy language target的步骤.    

数据节点

hostaddr 172.16.3.150    
port 1921    
user digoal  // plproxy将使用digoal用户连接数据节点.    
password digoal    

dbname db0    
schema digoal    
dbname db1    
schema digoal    
dbname db2    
schema digoal    
dbname db3    
schema digoal    

部署plproxy

首先在http://git.postgresql.org/gitweb/?p=plproxy.git;a=summary下载plproxy.

tar -zxvf plproxy-d703683.tar.gz    
mv plproxy-d703683 /opt/soft_bak/postgresql-9.3.1/contrib    
cd /opt/soft_bak/postgresql-9.3.1/contrib/plproxy-d703683    
[root@db-172-16-3-150 plproxy-d703683]# export PATH=/home/pg93/pgsql9.3.1/bin:$PATH    
[root@db-172-16-3-150 plproxy-d703683]# which pg_config    
[root@db-172-16-3-150 plproxy-d703683]# gmake clean    
[root@db-172-16-3-150 plproxy-d703683]# gmake    
[root@db-172-16-3-150 plproxy-d703683]# gmake install    

创建proxy库, proxy角色, 在proxy库创建plproxy extension.

pg93@db-172-16-3-150-> psql    
psql (9.3.1)    
Type "help" for help.    
postgres=# create role proxy nosuperuser login encrypted password 'proxy';    
CREATE ROLE    
digoal=# create database proxy;    
CREATE DATABASE    
digoal=# \c proxy    
You are now connected to database "proxy" as user "postgres".    
proxy=# create extension plproxy;    
CREATE EXTENSION    

调整proxy库权限

proxy=# grant all on database proxy to proxy;    
GRANT    
proxy=# \c proxy proxy    
You are now connected to database "proxy" as user "digoal".    

创建digoal schema, 目的是和数据节点的schema匹配, 这样的话可以省去在代理函数中写target强行指定schema.

proxy=> create schema digoal;    
CREATE SCHEMA    

创建节点数据库

proxy=> \c postgres postgres     
You are now connected to database "postgres" as user "postgres".     
postgres=# create role digoal nosuperuser login encrypted password 'digoal';     
postgres=# create database db0;    
postgres=# create database db1;    
postgres=# create database db2;    
postgres=# create database db3;    

调整权限, 赋予给后面将要给user mapping中配置的option user权限.

postgres=# grant all on database db0 to digoal;    
postgres=# grant all on database db1 to digoal;    
postgres=# grant all on database db2 to digoal;    
postgres=# grant all on database db3 to digoal;    

使用超级用户在proxy数据库中创建server.

proxy=> \c proxy postgres    
You are now connected to database "proxy" as user "postgres".    
proxy=#     
CREATE SERVER cluster_srv1 FOREIGN DATA WRAPPER plproxy options     
(connection_lifetime '1800',    
p0 'dbname=db0 hostaddr=172.16.3.150 port=1921 application_name=test',    
p1 'dbname=db1 hostaddr=172.16.3.150 port=1921',    
p2 'dbname=db2 hostaddr=172.16.3.150 port=1921',    
p3 'dbname=db3 hostaddr=172.16.3.150 port=1921');    

创建server时可以使用libpq中的选项. 例如本例使用了application_name.

将server权限赋予给proxy用户.

proxy=# grant usage on FOREIGN server cluster_srv1 to proxy;    
GRANT    

配置proxy用户的连接cluster_srv1的选项.

proxy=# create user mapping for proxy server cluster_srv1 options (user 'digoal');    
CREATE USER MAPPING    

用户proxy连接到cluster_srv1时使用digoal用户连接, 这里不需要配置password, 因为我们将使用trust认证.

修改数据节点的pg_hba.conf

从proxy节点使用digoal用户连接数据库db0, db1, db2, db3使用trust认证.

vi $PGDATA/pg_hba.conf    
host db0 digoal 172.16.3.150/32 trust    
host db1 digoal 172.16.3.150/32 trust    
host db2 digoal 172.16.3.150/32 trust    
host db3 digoal 172.16.3.150/32 trust    
pg_ctl reload    

在plproxy节点创建代理函数

使用超级用户创建plproxy函数, 然后把函数权限赋予给proxy权限.

proxy=# CREATE OR REPLACE FUNCTION digoal.dy(sql text)                      
 RETURNS SETOF record    
 LANGUAGE plproxy    
 STRICT    
AS $function$    
  cluster 'cluster_srv1';    
  run on all;    
$function$;    
proxy=# grant execute on function digoal.dy(text) to proxy;    
GRANT    

在数据节点创建实体函数

proxy=# \c db0 digoal    
db0=#     
CREATE OR REPLACE FUNCTION digoal.dy(sql text)    
 RETURNS SETOF record    
 LANGUAGE plpgsql    
 STRICT    
AS $function$    
  declare    
  rec record;    
  begin    
    for rec in execute sql loop    
      return next rec;    
    end loop;    
    return;    
  end;    
$function$;    
db0=# \c db1 digoal    
...    
db1=# \c db2 digoal    
...    
db2=# \c db3 digoal    
...    

在proxy节点中就可以访问数据节点了。

例如查询这个动态SQL.

proxy=> select * from digoal.dy('select count(*) from pg_class') as t(i int8);    
  i      
-----    
 293    
 293    
 293    
 293    
(4 rows)    
proxy=> select sum(i) from digoal.dy('select count(*) from pg_class') as t(i int8);    
 sum      
------    
 1172    
(1 row)    

plproxy节点测试

一. 修改foreign server测试, 观察连接将重置.

前面那个会话不要断开, 在另一个会话中观察proxy发起的连接到数据节点的连接.

postgres=# select * from pg_stat_activity where usename='digoal';    
 datid | datname | pid  | usesysid | usename | application_name | client_addr  | client_hostname | client_port |         backend_sta    
rt         | xact_start |          query_start          |         state_change          | waiting | state |                        q    
uery                            
-------+---------+------+----------+---------+------------------+--------------+-----------------+-------------+--------------------    
-----------+------------+-------------------------------+-------------------------------+---------+-------+-------------------------    
----------------------------    
 91246 | db0     | 8171 |    91250 | digoal  | test             | 172.16.3.150 |                 |       47937 | 2013-11-22 17:23:26    
.138425+08 |            | 2013-11-22 17:27:05.539286+08 | 2013-11-22 17:27:05.539745+08 | f       | idle  | select i::int8 from digo    
al.dy($1::text) as (i int8)    
 91247 | db1     | 8172 |    91250 | digoal  |                  | 172.16.3.150 |                 |       47938 | 2013-11-22 17:23:26    
.138688+08 |            | 2013-11-22 17:27:05.53938+08  | 2013-11-22 17:27:05.539874+08 | f       | idle  | select i::int8 from digo    
al.dy($1::text) as (i int8)    
 91248 | db2     | 8173 |    91250 | digoal  |                  | 172.16.3.150 |                 |       47939 | 2013-11-22 17:23:26    
.138957+08 |            | 2013-11-22 17:27:05.53938+08  | 2013-11-22 17:27:05.539841+08 | f       | idle  | select i::int8 from digo    
al.dy($1::text) as (i int8)    
 91249 | db3     | 8174 |    91250 | digoal  |                  | 172.16.3.150 |                 |       47940 | 2013-11-22 17:23:26    
.139178+08 |            | 2013-11-22 17:27:05.539366+08 | 2013-11-22 17:27:05.539793+08 | f       | idle  | select i::int8 from digo    
al.dy($1::text) as (i int8)    
(4 rows)    

再次在proxy的同一会话中查询时, 这些会话会复用, 不会断开. 前面已经讲了plproxy是使用长连接的.

如果修改了server, 那么这些连接会断开, 重新连接. 所以不需要担心修改server带来的连接cache问题.

postgres=# \c proxy postgres    
You are now connected to database "proxy" as user "postgres".    
proxy=# alter server cluster_srv1 options (set p1 'dbname=db1 hostaddr=172.16.3.150 port=1921 application_name=abc');    
ALTER SERVER    

再次在proxy的同一会话中查询后, 我们发现4个连接都变了, 说明alter server后, 如果再次发起plproxy函数的查询请求, 那么proxy会重置连接.

proxy=> select sum(i) from digoal.dy('select count(*) from pg_class') as t(i int8);    
 sum      
------    
 1172    
(1 row)    

在另一会话的查询结果 :

proxy=# select * from pg_stat_activity where usename='digoal';    
 datid | datname | pid  | usesysid | usename | application_name | client_addr  | client_hostname | client_port |         backend_sta    
rt         | xact_start |          query_start          |         state_change          | waiting | state |                        q    
uery                            
-------+---------+------+----------+---------+------------------+--------------+-----------------+-------------+--------------------    
-----------+------------+-------------------------------+-------------------------------+---------+-------+-------------------------    
----------------------------    
 91246 | db0     | 8245 |    91250 | digoal  | test             | 172.16.3.150 |                 |       47941 | 2013-11-22 17:30:36    
.933077+08 |            | 2013-11-22 17:30:36.936784+08 | 2013-11-22 17:30:36.938837+08 | f       | idle  | select i::int8 from digo    
al.dy($1::text) as (i int8)    
 91248 | db2     | 8247 |    91250 | digoal  |                  | 172.16.3.150 |                 |       47943 | 2013-11-22 17:30:36    
.933502+08 |            | 2013-11-22 17:30:36.936783+08 | 2013-11-22 17:30:36.938981+08 | f       | idle  | select i::int8 from digo    
al.dy($1::text) as (i int8)    
 91249 | db3     | 8248 |    91250 | digoal  |                  | 172.16.3.150 |                 |       47944 | 2013-11-22 17:30:36    
.933731+08 |            | 2013-11-22 17:30:36.937147+08 | 2013-11-22 17:30:36.939015+08 | f       | idle  | select i::int8 from digo    
al.dy($1::text) as (i int8)    
 91247 | db1     | 8246 |    91250 | digoal  | abc              | 172.16.3.150 |                 |       47942 | 2013-11-22 17:30:36    
.933288+08 |            | 2013-11-22 17:30:36.93757+08  | 2013-11-22 17:30:36.939299+08 | f       | idle  | select i::int8 from digo    
al.dy($1::text) as (i int8)    
(4 rows)    

二. run on 的几种形式, 表示数据路由方法.

在数据节点创建测试表.

proxy=# \c db0 digoal    
db0=> create table t(id int);    
CREATE TABLE    
db0=> \c db1    
You are now connected to database "db1" as user "digoal".    
db1=> create table t(id int);    
CREATE TABLE    
db1=> \c db2    
You are now connected to database "db2" as user "digoal".    
db2=> create table t(id int);    
CREATE TABLE    
db2=> \c db3    
You are now connected to database "db3" as user "digoal".    
db3=> create table t(id int);    
CREATE TABLE    

在数据节点创建插入数据的实体函数, 每个节点返回不一样的数字.

\c db0 digoal    
db0=> create or replace function digoal.f_test4() returns int as $$    
declare    
begin    
insert into t(id) values (1);    
return 0;    
end;    
$$ language plpgsql strict;    
db1=> create or replace function digoal.f_test4() returns int as $$    
declare    
begin    
insert into t(id) values (1);    
return 1;    
end;    
$$ language plpgsql strict;    
db2=> create or replace function digoal.f_test4() returns int as $$    
declare    
begin    
insert into t(id) values (1);    
return 2;    
end;    
$$ language plpgsql strict;    
db3=> create or replace function digoal.f_test4() returns int as $$    
declare    
begin    
insert into t(id) values (1);    
return 3;    
end;    
$$ language plpgsql strict;    

在proxy节点创建代理函数, 并且将执行权限赋予给proxy用户.

proxy=> \c proxy postgres    
create or replace function digoal.f_test4() returns int as $$    
cluster 'cluster_srv1';    
run on 0;   -- 在指定的数据节点上运行, 本例可以设置为0到3, 顺序和创建的server中的配置顺序一致. p0, p1, p2, p3    
$$ language plproxy strict;    
proxy=# grant execute on function digoal.f_test4() to proxy;    
GRANT    
proxy=# \c proxy proxy    
You are now connected to database "proxy" as user "proxy".    
proxy=> select * from digoal.f_test4();    
 f_test4     
---------    
       0    
(1 row)    

如果run on 的数字改成0-3以外的数字, 运行时将报错, 符合预期.

proxy=# create or replace function digoal.f_test4() returns int as $$    
cluster 'cluster_srv1';    
run on 4;      
$$ language plproxy strict;    
CREATE FUNCTION    
proxy=# \c proxy proxy    
You are now connected to database "proxy" as user "proxy".    
proxy=> select * from digoal.f_test4();    
ERROR:  PL/Proxy function digoal.f_test4(0): part number out of range    

run on any表示随机的选择一个数据节点运行.

proxy=> \c proxy postgres    
You are now connected to database "proxy" as user "postgres".    
proxy=# create or replace function digoal.f_test4() returns int as $$    
cluster 'cluster_srv1';    
run on any;      
$$ language plproxy strict;    
CREATE FUNCTION    
proxy=# \c proxy proxy    
You are now connected to database "proxy" as user "proxy".    
proxy=> select * from digoal.f_test4();    
 f_test4     
---------    
       0    
(1 row)    

proxy=> select * from digoal.f_test4();    
 f_test4     
---------    
       3    
(1 row)    

proxy=> select * from digoal.f_test4();    
 f_test4     
---------    
       2    
(1 row)    

proxy=> select * from digoal.f_test4();    
 f_test4     
---------    
       3    
(1 row)    

run on function() 则使用函数结果的hash值计算得到运行节点.

proxy=> create or replace function digoal.f(int) returns int as $$    
select $1;    
$$ language sql strict;    
CREATE FUNCTION    
proxy=> \c proxy postgres    
You are now connected to database "proxy" as user "postgres".    
proxy=# create or replace function digoal.f_test4() returns int as $$    
cluster 'cluster_srv1';    
run on digoal.f(10);      
$$ language plproxy strict;    
CREATE FUNCTION    
proxy=> select digoal.f_test4();    
 f_test4     
---------    
       2    
(1 row)    
proxy=> \c proxy postgres    
You are now connected to database "proxy" as user "postgres".    
proxy=# create or replace function digoal.f_test4() returns int as $$    
cluster 'cluster_srv1';    
run on digoal.f(11);      
$$ language plproxy strict;    
CREATE FUNCTION    
proxy=# \c proxy proxy    
You are now connected to database "proxy" as user "proxy".    
proxy=> select digoal.f_test4();    
 f_test4     
---------    
       3    
(1 row)    
proxy=> \c proxy postgres    
You are now connected to database "proxy" as user "postgres".    
proxy=# create or replace function digoal.f_test4() returns int as $$    
cluster 'cluster_srv1';    
run on digoal.f(-11);      
$$ language plproxy strict;    
CREATE FUNCTION    
proxy=# \c proxy proxy    
You are now connected to database "proxy" as user "proxy".    
proxy=> select digoal.f_test4();    
 f_test4     
---------    
       1    
(1 row)    

run on all表示所有数据节点运行. 代理函数必须使用returns setof返回.

proxy=> \c proxy postgres    
You are now connected to database "proxy" as user "postgres".    
proxy=# create or replace function digoal.f_test4() returns int as $$    
cluster 'cluster_srv1';    
run on all;                
$$ language plproxy strict;    
ERROR:  PL/Proxy function digoal.f_test4(0): RUN ON ALL requires set-returning function    
proxy=# drop function digoal.f_test4();    
DROP FUNCTION    
proxy=# create or replace function digoal.f_test4() returns setof int as $$    
cluster 'cluster_srv1';    
run on all;      
$$ language plproxy strict;    
CREATE FUNCTION    
proxy=# grant execute on function digoal.f_test4() to proxy;    
GRANT    
proxy=# \c proxy proxy     
You are now connected to database "proxy" as user "proxy".    
proxy=> select digoal.f_test4();    
 f_test4     
---------    
       0    
       1    
       2    
       3    
(4 rows)    

注意事项

1. 设计时需要注意

plproxy函数所在的schema尽量和数据节点上实际函数的schema一致.

否则需要在plproxy函数中使用target指定 schema.functionname;

2. 数据节点的个数请保持2^n,

这么做有利于后期的节点扩展, 例如2个节点扩展到4个节点时, 数据不需要发生跨节点的重分布.

例如

mod(x,2)=0 那么mod(x,4)=0或2    
mod(x,2)=1 那么mod(x,4)=1或3    

比较适合位运算的分布算法.

当然我们也可以使用一致性哈希的设计思路,参考

《一致性哈希在分布式数据库中的应用探索》
https://yq.aliyun.com/articles/57954

3. 如果业务为短连接的形式, 那么需要1层连接池, 在应用程序和plproxy数据库之间. 而不是plproxy和数据节点之间.

在应用程序和plproxy之间加连接池后, 其实对于plproxy来说就是长连接了, 所以在plproxy和数据节点之间也就不需要连接池了.

4. 长连接不需要连接池, 因为plproxy和数据节点之间的连接是长连接.

5. plproxy语法非常简洁,而且函数调用彻底避免了事务的问题

connect, cluster, run, select, split, target.  

6. 关于连接密码

出于安全考虑, 建议在任何配置中不要出现明文密码, 所以最好是plproxy服务器到数据节点是trust验证, 保护好plproxy即可.

假设plproxy在172.16.3.2上. 数据节点有4个, 库名和用户名都为digoal. 那么在4个节点上配置pg_hba.conf如下.

   node0    
   host digoal digoal 172.16.3.2/32 trust    
   node1    
   host digoal digoal 172.16.3.2/32 trust    
   node2    
   host digoal digoal 172.16.3.2/32 trust    
   node3    
   host digoal digoal 172.16.3.2/32 trust    

7. run 详解:

   run on <NR>, <NR>是数字常量, 范围是0 到 nodes-1; 例如有4个节点 run on 0; (run on 4则报错).    
   run on ANY,     
   run on function(...), 这里用到的函数返回结果必须是int2, int4 或 int8.     
   run on ALL, 这种的plproxy函数必须是returns setof..., 实体函数没有setof的要求.    

8. 一个plproxy中只能出现一条connect语句, 符合预期, 否则报错.

digoal=# create or replace function f_test3() returns setof int8 as $$    
  connect 'hostaddr=172.16.3.150 dbname=db0 user=digoal port=1921';      
  connect 'hostaddr=172.16.3.150 dbname=db1 user=digoal port=1921';                                  
  select count(*) from pg_class;    
$$ language plproxy strict;    
ERROR:  PL/Proxy function postgres.f_test3(0): Compile error at line 2: Only one CONNECT statement allowed    

9. 不要把plproxy语言的权限赋予给普通用户, 因为开放了trust认证, 如果再开放plproxy语言的权限是非常危险的.

正确的做法是使用超级用户创建plproxy函数, 然后把函数的执行权限赋予给普通用户.

千万不要这样省事 :

update pg_language set lanpltrusted='t' where lanname='plproxy';    

10. 如果有全局唯一的序列需求, 可以将序列的步调调整一下, 每个数据节点使用不同的初始值.
例如

db0=# create sequence seq1 increment by 4 start with 0;    
CREATE SEQUENCE    
db1=# create sequence seq1 increment by 4 start with 1;    
db2=# create sequence seq1 increment by 4 start with 2;    
db3=# create sequence seq1 increment by 4 start with 3;    

考虑到扩容, 可以将步调调比较大, 例如1024. 那么可以容纳1024个节点.

参考

1. http://kaiv.wordpress.com/2007/07/27/postgresql-cluster-partitioning-with-plproxy-part-i/

2. http://kaiv.wordpress.com/2007/09/02/postgresql-cluster-partitioning-with-plproxy-part-ii/

3. http://blog.163.com/digoal@126/blog/static/163877040201041111304328/

4. http://blog.163.com/digoal@126/blog/static/1638770402010411113114315/

5. http://blog.163.com/digoal@126/blog/static/163877040201192535630895/

6. http://www.postgresql.org/docs/9.3/static/libpq-connect.html#LIBPQ-CONNSTRING

7. http://git.postgresql.org/gitweb/?p=plproxy.git;a=summary

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