Sga and Kernel parameters

During database configuration, the limitations of sga generally come from three aspects:

1. Physical memory and available swap2. Kernel parameter SHMMAX3. Restrictions on shared memory for other operating systems

Usually, the configuration of kernel parameters will affect the configuration of some parameters in sga. The corresponding relationship between kernel parameters and init.ora is as follows:

Init.ora ParameterKernel Parameterdb_block_buffersshmmax, shmalldb_files (maxdatafiles)nfile, maxfileslarge_pool_sizeshmmax, shmalllog_buffershmmax, shmallprocessesnproc, semmsl, semmnsshared_pool_sizeshmmax, shmall

General parameter description:

maxfiles -soft file limit per process. maxuprc -Maximum number of concurrent user processes per user identity. nfile -The maximum number of files open systemwide at any given time. nproc -Maximum number of processes that can exist simultaneously in the system. shmall -This parameter sets the total number of shared memory pages available system-wide. Therefore, shmall should always be at least ceiling (shmmax / page_size). shmmax -Maximum size of a single shared memory segment in bytes. SHMMIN -Minimum size of a single shared memory segment in bytes. shmmni -Number of shared memory identifiers. shmseg -Maximum number of shared memory segments that a process can attach. semmns -Number of semaphores in the system. semmni -Number of semaphore set identifiers in the system; determines the number of semaphore sets that can be created at any time. semmsl -Maximum number of sempahore that can be contained in a semaphore set. It should be the same as the maximum number of Oracle processes.