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This article introduces the knowledge of "how to understand the sysctl.conf kernel parameters in Oracle". Many people will encounter this dilemma in the operation of actual cases, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

Note: most of the kernel parameters of OS are stored in the / proc/sys directory, which can be changed while the system is running, but will fail when the system is rebooted, and the modified kernel parameters can be permanently taken effect through the / etc/sysctl.conf file.

Sysctl-p

This command immediately takes effect the kernel parameters configured in sysctl.conf.

The following are the kernel parameters that need to be configured when installing and deploying Oracle:

Cat / etc/sysctl.conf

Kernel.shmall

Shmall represents the total shared memory in pages, while the default value of 4294967296 is large enough and generally does not need to be adjusted. Shmall cannot be lower than the SGA size. If the shmall is lower than the SGA size, the instance will report an error "ORA-27123: unable to attach to shared memory segment" when starting, and the instance cannot be started.

Kernel.shmmax

The shmmax parameter is used to define the maximum value of a single shared memory segment, which should be configured large enough to accommodate the entire SGA in one shared memory segment. If the configuration is too low, multiple shared memory segments may need to be created, which may lead to system performance degradation.

269838450688/1024/1024/1024=252GB .

The unit of shmmax is Byte (bytes).

Vm.min_free_kbytes

This parameter indicates the minimum amount of free memory reserved by Linux VM. When the available memory is lower than the configuration parameter, the system will reclaim the cache memory to release the memory.

The unit is kb,524288/1024=512M.

Kernel.sem

Sem is an acronym for semaphores. Interprocess communication-semaphores. Four parameters in kernel.sem correspond to SEMMSL SEMMNS SEMOPM SEMMNI.

SEMMSL: the maximum number of signals per semaphore set. Generally, this parameter is configured as the setting value of the maximum PROCESS parameter in the database plus 10 Oracle recommends that SEMMSL not be less than 100.

SEMMNS: controls the maximum number of semaphores in the entire system, using the following calculation formula to determine the maximum number of signals to be configured in the system, (SEMMSL * SEMMNI) = SEMMNS. 4096, 128, 524288.

SEMOPM: this parameter represents the maximum number of operations allowed per semaphore in a semop call. A signal set can have the maximum number of SEMMSL signals in each signal set. It is recommended that SEMOPM equals SEMMSL. Oracle recommends that the value of SEMOPM be no less than 100.

SEMMNI: this parameter is used to control the maximum number of signal sets in the system. Oracle recommends that the value of SEMMNI be no less than 100.

Fs.file-max

This parameter represents the maximum number of file handles that can be opened at the system level, and the file handle represents the number of files in the system that can be opened.

Net.ipv4.ip_local_port_range

This parameter configures the outward connection port range, which defaults to 1024 to 4999.

Net.ipv4.ipfrag_*

Net.ipv4.ipfrag_low_thresh

Net.ipv4.ipfrag_high_thresh

When a packet transmission error occurs in the system, it will be defragmented, valid packets will be retained, and invalid packets will be discarded. The ipfrag parameter specifies the maximum / minimum memory for defragmentation.

Net.core.rmem_*

Net.core.rmem_default default data receive window size.

Net.core.rmem_max most big data receive window size.

Net.core.wmem_default default data send window size.

Net.core.wmem_max most big data send window size.

The units are all bytes.

Fs.aio-max-nr

This parameter represents the maximum number of concurrent asynchronous I-Unable to Reserve Kernel Resources for Asynchronous Disk O requests. When there are very high I-Unable to Reserve Kernel Resources for Asynchronous Disk O requests in the system, if this parameter is configured too low, it may cause the database to report an error of "ORA-27090-asynchronous". If you encounter this problem, you need to adjust the fs.aio-max-nr to the recommended Oracle value of 3145728.

Note: Doc ID 579108.1

Kernel.shmmni

This parameter is the maximum number of shared memory segments, with a default value of 4096, which generally does not need to be adjusted.

Vm.nr_hugepages

This parameter specifies the number of large pages of memory and the number of large pages of memory in units.

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