Flashcache in Oralce

Usage conditions: For Linux or Solaris machines, doulebuffercache is recommended in AWR. dbfilesequentialread is topwaitevent. The size is 2-10 times the bufferc size.

Usage conditions: For Linux or Solaris machines, we recommend doule buffer cache in AWR. db file sequential read is top wait event. buffer c of 2 to 10 times the size.

Usage conditions:
For Linux or Solaris machines, we recommend doule buffer cache in AWR, and db file sequential read is the top wait event.

Size:
2-10 times the buffer cache. It cannot be less than 2 times. If ASMM is used, 2-10 times the SGA_TARGET

Two parameters:
DB_FLASH_CACHE_FILE
Specifies a list of paths and file names for the files to contain the flash cache, in either the operating system file system or an Oracle Automatic IC Storage Management disk group. if a specified file does not exist, the database creates it during startup. each file must reside on a flash disk device. if you configure the flash cache on a disk drive (spindle), performance may suffer. A maximum of 16 files is supported.

DB_FLASH_CACHE_SIZE
Specifies the size of each file in the flash cache. each size corresponds with a file specified in db_flash_cache_file. the files and sizes correspond in the order that they are specified. an error is raised if the number of specified sizes does not match the number of specified files.
Each size specification must be less than or equal to the physical memory size of its flash disk device. the size is expressed as nG, indicating the number of gigabytes (GB ). for example, to specify a 16 GB flash cache, set db_flash_cache_size value to 16 GB.

Usage:
Alter system set altdb_flash_cache_file = '/dev/raw/sda' scope = spfile;
Alter system set db_flash_cache_size = 32G scope = spfile;

You can set db_flash_cache_size to 0 to disable flash cache. enable can be set again. However, you cannot dynamically modify the value of db_flash_cache_size.

For the RAC environment, you must set the above two parameters on each instance and cannot use the same file.

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