Shulou(Shulou.com)06/01 Report--

1. Kernel.shmmax:

Is one of the most important core parameters that defines the maximum value of a single shared memory segment. The setting should be large enough to accommodate the entire SGA under one shared memory segment, and a low setting may result in the need to create multiple shared memory segments, which may lead to system performance degradation. The main reason for the system decline is that when the instance is started and the ServerProcess is created, multiple small shared memory segments may lead to a slight degradation of system performance at that time (multiple virtual address fields need to be created at startup, and there will be some impact when the process is created to let the process "identify" multiple segments), but it will not be affected at other times.

Official recommended values:

32-bit linux system: the maximum preferred value is 4GB (4294967296bytes)-1byte, which is 4294967295. The recommended value is more than half of the memory, so if 32 is the system, the value is generally 4294967295. 32-bit systems have limits on the size of the SGA, so the SGA can certainly be included in a single shared memory segment.

64-bit linux system: the maximum preferred value is the physical memory value-1byte, and the recommended value is more than half of the physical memory. Generally, the value is greater than SGA_MAX_SIZE. You can take the physical memory-1byte.

When the memory is 12g, the value is 1284901887.

When the memory is 16G, the value is 16,1024,1024,1024-1 = 17179869183.

When the memory is 32 GB, the value is 32 "1024" 1024 "1024-1 = 34359738367.

When the memory is 64g, the value is 641024102410241024-1 = 68719476735

When the memory is 128 GB, the value is 128 "1024" 1024 "1024-1 = 137438953471.

2. Kernel.shmall:

This parameter controls the total number of pages of shared memory that can be used. The page size of Linux shared memory is 4KB, and the size of shared memory segments is an integral multiple of the size of shared memory pages.

The maximum size of a shared memory segment is 16G, so the number of pages that need to be shared memory is 16GB/4KB==4194304 (pages).

When the memory is 12g, kernel.shmall = 3145728

When the memory is 16GB, kernel.shmall = 4194304

When the inner time is 32G, kernel.shmall = 8388608

When the memory is 64GB, kernel.shmall = 16777216

When the memory is 128 GB, kernel.shmall = 33554432

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