5.2.3.8 Using XRMEM Cache Attributes

You can use XRMEM cache attributes in the IORM plan to guarantee space allocation in the Exadata RDMA Memory Cache (XRMEM cache).

Using XRMEM cache attributes, IORM can reserve space for critical databases while preventing less important or rogue entities from consuming the entire XRMEM cache. These attributes can only be specified in an interdatabase plan, and are configured using the CellCLI utility.

You can use the following attributes to set limits for XRMEM cache resources. A hard limit means the database cannot exceed its quota even when the memory cache is not full. A soft limit means that the specified limit can be exceeded if there are available resources.

• xrmemCacheMin — Specifies the minimum amount of XRMEM cache space that is guaranteed for the specified database, even if the blocks are cold. This is a hard limit.

  Because xrmemCacheMin is a guaranteed reservation, the sum of xrmemCacheMin across all directives should be less than the size of the XRMEM cache to ensure that each database gets its respective quota.

• xrmemCacheLimit — Specifies the soft maximum amount of XRMEM cache space that is available to the database. If the XRMEM cache is not full, a database can exceed the xrmemCacheLimit value.

• xrmemCacheSize — Specifies the hard maximum amount of XRMEM cache space that is available to the database. The xrmemCacheSize value cannot be exceeded at any time.

  However, if you set xrmemCacheSize to a value that is lower than the current space occupied by the database, then excess data is proactively cleared from the cache.

  xrmemCacheSize is not a guaranteed reservation if the sum of the xrmemCacheSize across all directives is more than the size of the XRMEM cache. In this case, you can also specify xrmemCacheMin to define a guaranteed minimum quota.

  Note:

  On Exadata X8M and X9M storage server models only, you can interchangeably use attribute names starting with pmem instead of xrmem. For example, pmemCacheMin instead of xrmemCacheMin. However, you cannot have a mixture of PMEM and XRMEM attributes in the IORM plan.

Example 5-12 Configuring an Interdatabase Plan with XRMEM Cache Attributes

This example shows how to create an interdatabase plan with XRMEM cache attributes.

In the example, the sales and test databases are allocated an amount of space in the XRMEM cache by using the xrmemCacheSize parameter. But, the databases cannot exceed the specified allocation, even if the XRMEM cache has free space.

The finc and dev databases use xrmemCacheMin for guaranteed minimum quotas. These databases can also exceed the specified xrmemCacheLimit size when there is free space in the XRMEM cache.

The example plan also contains various flash cache attributes.

ALTER IORMPLAN dbplan=                                                                             -
((name=sales, share=8, xrmemCacheSize=2G, flashCacheSize=10G),                                     -
(name=finc, share=8, xrmemCacheMin=1G, xrmemCacheLimit=2G, flashCacheLimit=10G, flashCacheMin=2G), -
(name=dev, share=2, xrmemCacheMin=500M, xrmemCacheLimit=1G, flashCacheLimit=4G, flashCacheMin=1G), -
(name=test, share=1, limit=10, xrmemCacheSize=200M))