7.7.4.8 CREATE PMEMCACHE

Purpose

The CREATE PMEMCACHE command creates a persistent memory (PMEM) cache for I/O requests.

Note:

The CREATE PMEMCACHE command can only be used on Exadata X8M and X9M storage server models.

Syntax

CREATE PMEMCACHE { ALL [ size = cache_size ] | 
          CELLDISK='cdisk1[,cdisk2]...' [ , size=cache_size ] }

Usage Notes

• The ALL argument creates the PMEM cache on all PMEM cell disks. If the ALL argument is not specified, then specific PMEM cell disks must be specified by using the CELLDISK argument. The PMEM cache is spread as evenly as possible across the PMEM cell disks.

• PMEM cache space is allocated in 16 MB chunks, referred to as allocation units, with a minimum of 1 allocation unit. Consequently, when the size argument is specified, the actual space allocated to the PMEM cache is at least 16 MB or the largest multiple of 16 MB that is less than or equal to the specified size. For example, if size=500M is specified, then 496 MB is allocated using 31 allocation units.

• Before specifying the size attribute, use the following command to check the available free space on the PMEM cell disks:

  LIST CELLDISK ATTRIBUTES freespace WHERE disktype=PMEM

• If the size attribute is not specified, then the PMEM cache consumes all of the available space (allocation units).

• Cell disks used by the PMEM cache cannot be exported.

• On Exadata X8M and X9M systems with Oracle Exadata System Software release 23.1.0, you can interchangeably use CREATE XRMEMCACHE instead of CREATE PMEMCACHE.

Examples

Example 7-88 Creating PMEM Cache

The following command demonstrates how to create a 64 GB PMEM cache on specific PMEM cell disks.

CREATE PMEMCACHE celldisk='PM_01_mycell,PM_02_mycell', size = 64G

The following command demonstrates how to create a 64 GB PMEM cache using all PMEM cell disks.

CREATE PMEMCACHE ALL size = 64G