本文转自
https://blog.hackroad.com/operations-engineer/linux_server/13212.html
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在PostgreSQL9.5之前的版本中，修改系统参数一般的步骤是：
1、连接到PostgreSQL数据库服务器；
2、打开postgresql.conf文件，找到需要修改的参数，修改参数的值为所需要的值；
3、执行restart或reload使修改生效；
还有一点比较不方便的是，不能很直观的看到需要重启才生效的参数到底生效了没有，只能把参数show出来观察是否满足预期。
在PostgreSQL9.5中，增加了ALTER SYSTEM命令，并且在pg_settings视图中增加了pending_restart(boolean)列，该列标识了是否在重启之后才生效，使得修改参数和查看参数是否生效都方便了很多。步骤可以简化为：
1、执行ALTER SYSTEM命令
2、执行restart或reload使修改生效；
对于脚本的支持也好了很多，而且通过ALTER SYSTEM配置的参数都会保存在postgresql.auto.conf文件中，需要清除这些配置也只需要一条命令就可以很方便的处理完成，下面有详细的解释。
ALTER SYSTEM语法
vincent=# h ALTER SYSTEM
Command: ALTER SYSTEM
Description: change a server configuration parameter
Syntax:
ALTER SYSTEM SET configuration_parameter { TO | = } { value | 'value' | DEFAULT }
ALTER SYSTEM RESET configuration_parameter
ALTER SYSTEM RESET ALL |
vincent=# h ALTER SYSTEMCommand: ALTER SYSTEMDescription: change a server configuration parameterSyntax:ALTER SYSTEM SET configuration_parameter { TO | = } { value | 'value' | DEFAULT }ALTER SYSTEM RESET configuration_parameterALTER SYSTEM RESET ALL
示例
举两个例子，一个是shared_buffers参数，该参数需要重启生效；另一个是work_mem参数，该参数只需要pg_ctl reload或SELECT pg_reload_conf();就可以生效。
通过show命令查看，当前的shared_buffers的值为128MB
# show shared_buffers;
shared_buffers
----------------
128MB
(1 row) |
vincent=# show shared_buffers; shared_buffers ---------------- 128MB(1 row)
也可以直接从pg_settings表中去查
# x
Expanded display is on.
# select * from pg_settings where name = 'shared_buffers';
-[ RECORD 1 ]---+-------------------------------------------------------------
name | shared_buffers
setting | 16384
unit | 8kB
category | Resource Usage / Memory
short_desc | Sets the number of shared memory buffers used by the server.
extra_desc |
context | postmaster
vartype | integer
source | configuration file
min_val 16
max_val 1073741823
enumvals |
boot_val 1024
reset_val 16384
sourcefile /opt/pgdev/data/postgresql.conf
sourceline 115
pending_restart | f |
vincent=# xExpanded display is on.vincent=# select * from pg_settings where name = 'shared_buffers';-[ RECORD 1 ]---+-------------------------------------------------------------name | shared_bufferssetting | 16384unit | 8kBcategory | Resource Usage / Memoryshort_desc | Sets the number of shared memory buffers used by the server.extra_desc | context | postmastervartype | integersource | configuration filemin_val | 16max_val | 1073741823enumvals | boot_val | 1024reset_val | 16384sourcefile | /opt/pgdev/data/postgresql.confsourceline | 115pending_restart | f
执行ALTER SYSTEM命令修改shared_buffers为1GB
# ALTER SYSTEM SET shared_buffers = '1GB';
ALTER SYSTEM |
vincent=# ALTER SYSTEM SET shared_buffers = '1GB';ALTER SYSTEM
查看pg_settings表，有哪些参数在等待生效：
# select name,setting,category,source,sourcefile,pending_restart from pg_settings where pending_restart = true;
-]---+--------------------------------
name 16384
category / Memory
file
sourcefile /postgresql.conf
pending_restart | t |
vincent=# select name,pending_restart from pg_settings where pending_restart = true;-[ RECORD 1 ]---+--------------------------------name | shared_bufferssetting | 16384category | Resource Usage / Memorysource | configuration filesourcefile | /opt/pgdev/data/postgresql.confpending_restart | t
重新启动DB
vincent@dellpad:~$ pg_ctl -D / -m fast restart |
vincent@dellpad:~$ pg_ctl -D /opt/pgdev/data/ -m fast restart
通过查询pg_settings表看到shared_buffers已经生效
| setting | category | source | sourcefile | pending_restart
----------------+---------+-------------------------+--------------------+--------------------------------------+-----------------
shared_buffers 131072 / Memory file /postgresql.auto.conf | f
) |
vincent=# select name,pending_restart from pg_settings where name='shared_buffers'; name | setting | category | source | sourcefile | pending_restart ----------------+---------+-------------------------+--------------------+--------------------------------------+----------------- shared_buffers | 131072 | Resource Usage / Memory | configuration file | /opt/pgdev/data/postgresql.auto.conf | f(1 row)
如果想清除所有通过ALTER SYSTEM命令配置的参数值，执行
# ALTER SYSTEM RESET ALL;
ALTER SYSTEM |
vincent=# ALTER SYSTEM RESET ALL;ALTER SYSTEM
下面是对work_mem的修改，就不逐步解释了
# ALTER SYSTEM SET work_mem = '1MB';
ALTER SYSTEM
#
| unit | source | sourcefile | pending_restart
----------+---------+------+-------------------------+---------+------------+-----------------
work_mem 4096 | kB | default | )
# select pg_reload_conf();
pg_reload_conf
----------------
t
| pending_restart
----------+---------+------+-------------------------+--------------------+--------------------------------------+-----------------
work_mem 1024 # !! cat /opt/pgdev/data/postgresql.auto.conf
# Do not edit this file manually!
# It will be overwritten by ALTER SYSTEM command.
work_mem = '1MB'
# |
