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1. Shmall and shmmax parameters of the kernel

SHMMAX = the size of the maximum memory segment configured-> this setting is better than SGA_MAX_SIZE.

SHMMAX parameter: the maximum value of a separate shared memory segment that can be allocated by the Linux process. It is generally set to half the total memory size. The setting of this value should be greater than the value of SGA_MAX_TARGET or MEMORY_MAX_TARGET, so for systems where Oracle databases are installed, the value of shmmax should be greater than 1/2 of memory.

The size of the minimum memory segment for SHMMIN=.

SHMMNI= the total number of memory segment for the entire system. Sets the maximum number of shared memory segments at the system level. Oracle10g recommends a minimum value of 4096, which can be appropriately increased compared to 4096.

SHMSEG= the maximum number of memory segment that can be used per process

Shmall = is the size of all allowed shared memory, and shmmax is the size allowed for a single segment. These two can be set to 90% of memory. For example, 16 gigabytes of memory, 16 "1024" 1024 "1024" 90% = 15461882265 the size of the shmall is 15461882265max 4k (available by getconf PAGESIZE) = 3774873.

Shmall sets the total number of pages in shared memory. It is possible that this value is too small to cause a database startup error. Many people only pay attention to the SHMMAX parameter when adjusting the system kernel parameters, ignoring the setting of the SHMALL parameter.

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two。 Configure parameters for semaphores (semphore)

Semaphores semaphores are counters that provide synchronization when processes or threads access shared memory.

SEMMSL= sets the maximum number of semaphores in each semaphore group, and the recommended minimum value is 250. For systems with a large number of concurrent connections, it is recommended that this value be set to the PROCESSES initialization parameter plus 10.

SEMMNI= sets the maximum number of semaphore groups in the system. The recommended values for Oracle10g and 11g are 142g.

SEMMNS= sets the maximum number of semaphores in the system. The operating system does not exceed LEAST (SEMMNS, SEMMSL*SEMMNI) when assigning semaphores. In fact, if the value of SEMMNS exceeds SEMMSL*SEMMNI, it is illegal, so the recommended value of SEMMNS is set to SEMMSL*SEMMNI. Oracle recommends that the setting of SEMMNS should not be less than 32000. If the PROCESSES parameter of the database is set to 600, the setting of SEMMNS should be:

SQL > select (600-10) * 142 from dual; (600-10) * 142-8662012345

SEMOPM parameter: sets the maximum number of semaphore operations that can be performed simultaneously per system call. Since a semaphore group can have up to SEMMSL semaphores, it is recommended that SEMOPM be set to the value of SEMMSL. The configuration of SEMOPM for 10.2 and 11.1 verified by Oracle is 100.

You can check the semaphore-related configuration with the following command:

# cat / proc/sys/kernel/sem250 32000 100 12812

The corresponding four values from left to right are SEMMSL, SEMMNS, SEMOPM and SEMMNI.

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3. Modify / etc/sysctl.conf

Kernel.shmmax=15461882265

Kernel.shmall=3774873

Kernel.msgmax=65535

Kernel.msgmnb=65535

Execute sudo sysctl-p

You can use ipcs-l to see the results, ipcs-u can see the actual use of the situation

This article is from: https://blog.csdn.net/sunansheng/article/details/51889044

Thanks to the original author

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