Postgres与OS内核相关的几个参数设置

--内核参数文件位置:
/proc/sys/kernel
/etc/sysctl.conf
[root@localhost ~]# sysctl -a|more
kernel.shmmax = 68719476736
kernel.shmall = 4294967296
kernel.shmmni = 4096
kernel.msgmax = 65536
kernel.msgmni = 2005
kernel.msgmnb = 65536
[postgres@localhost ~]$ cat /proc/sys/kernel/sem
250     32000   32      128
(semmsl  semmns  semopm  semmni)

[root@localhost ~]# free -m
             total       used       free     shared    buffers     cached
Mem:          1006        872        134          0        100        629
-/+ buffers/cache:        142        863
Swap:         2015         13       2002
[root@localhost ~]# su - postgres
[postgres@localhost ~]$ vi /database/pgdata/postgresql.conf 
shared_buffers = 5GB
[postgres@localhost ~]$ pg_start
server starting
[postgres@localhost ~]$ FATAL:  could not create shared memory segment: Cannot allocate memory
DETAIL:  Failed system call was shmget(key=1949001, size=5609447424, 03600).
HINT:  This error usually means that PostgreSQL's request for a shared memory segment exceeded available memory or swap space, or exceeded your kernel's SHMALL parameter.  You can either reduce the request size or reconfigure the kernel with larger SHMALL.  To reduce the request size (currently 5609447424 bytes), reduce PostgreSQL's shared memory usage, perhaps by reducing shared_buffers or max_connections.
        The PostgreSQL documentation contains more information about shared memory configuration.

解决办法是减小shared_buffers、max_connections值，也或者加大shmall值、shmax值、加大内存和swap，如果设置超大，大过内核值，则直接报错Invalid argument，如

[postgres@localhost ~]$ vi /database/pgdata/postgresql.conf
shared_buffers = 222222GB
max_connections = 100
[postgres@localhost ~]$ pg_start
server starting
[postgres@localhost ~]$ FATAL:  invalid value for parameter "shared_buffers": "222222GB"
HINT:  Value exceeds integer range. 

[postgres@localhost ~]$ vi /database/pgdata/postgresql.conf 
max_connections = 5000
[postgres@localhost ~]$ pg_start
server starting
[postgres@localhost ~]$ FATAL:  could not create semaphores: No space left on device
DETAIL:  Failed system call was semget(1949125, 17, 03600).
HINT:  This error does *not* mean that you have run out of disk space.  It occurs when either the system limit for the maximum number of semaphore sets (SEMMNI), or the system wide maximum number of semaphores (SEMMNS), would be exceeded.  You need to raise the respective kernel parameter.  Alternatively, reduce PostgreSQL's consumption of semaphores by reducing its max_connections parameter.
        The PostgreSQL documentation contains more information about configuring your system for PostgreSQL.

[root@localhost ~]# sysctl -w kernel.sem="500 64000 50 150"
kernel.sem = 500 64000 50 150
[root@localhost ~]# cat /proc/sys/kernel/sem
500     64000   50      150