SHMMAX Max in Linux x86 and x86-64 Systems

SHMMAX Max in Linux x86 and x86-64 Systems

SHMMAX Max in Linux x86 and x86-64 Systems
 
Reference Original:
Maximum SHMMAX values for Linux x86 and x86-64 (Document ID 567506.1)
 
Objectives:
 
Question:-bit (x86) maximum value in Linux system?
Question 2: What is the maximum value in 64-bit (x86-64) Linux system?
 
Solution:
Answer 1:
The maximum SHMMAX value recommended by Oracle Global Customer Support is less than 4 GB or 4294967295
 
The maximum size of a shared memory segment is limited by the available user addressing space. In a 32-bit system, it is 4 GB.
 
Answer 2:
Oracle Global Customer Support officially recommends that the maximum SHMMAX value is 1/2 of the physical memory.
The maximum size of a shared memory end is limited by the available user addressing space. In a 64bit system, this theoretical value is the power of 64 of 2. Therefore, the SHMMAX theoretical limit value is the size of the physical memory. However, the actual use of all memory as SHMMAX may lead to a potential situation: no memory can be used to do other things.
Therefore, the more ideal physical limit for SHMMAX is physical memory-2 GB
 
In the oracle db environment, this physical limit still causes insufficient memory for other required functions (functions ). Therefore, "Oracle maximum" for SHMMAX is generally 1/2 of the physical memory. Many Oracle customers a higher fraction, at their discretion
 
Occasionally, the customer may mistakenly think that it is incorrect to set SHMMAX according to the recommendation to limit all sga. Setting SHMMAX based on the recommendation will only cause some shared memory segments to be used on total sga. For details, see the mos article:
Document 15566.1, "SGA, SHMMAX, Semaphores and Shared Memory Explained"
In terms of memory configuration, the kernel parameter kernel. shmall also needs to be considered. This parameter is the size of all the shared memory that can be used by the system at a time, in the unit of page.
See the mos article:
Document 301830.1 Upon startup of Linux database get ORA-27102: out of memory Linux-X86_64 Error: 28: No space left on device and recommendations.

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