5.2.3.6 Using Flash Cache Attributes
You can use flash cache attributes in the IORM plan to guarantee space allocation in Exadata Smart Flash Cache.
Using flash cache attributes, IORM can reserve space for critical databases while preventing less important or rogue entities from consuming the entire flash 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 flash cache resources. A hard limit means that the specified limit cannot be exceeded even when the memory cache is not full. A soft limit means that the specified limit can be exceeded if there are available resources.
-
flashCacheMin
— Specifies the minimum amount of flash cache space that is guaranteed for the specified database, even if the blocks are cold. This is a hard limit.Because
flashCacheMin
is a guaranteed reservation, the sum offlashCacheMin
across all directives should be less than the size of the flash cache to ensure that each database gets its respective quota. flashCacheLimit
— Specifies the soft maximum amount of flash cache space that is available to the database. If the flash cache is not full, a database can exceed theflashCacheLimit
value.-
flashCacheSize
— Specifies the hard maximum amount of flash cache space that is available to the database. TheflashCacheSize
value cannot be exceeded at any time.However, if you set
flashCacheSize
to a value that is lower than the current space occupied by the database, then starting with Oracle Exadata System Software release 20.1.0 excess data is proactively cleared from the cache. Previously, excess data was only removed when overwritten by other data.Starting with Oracle Exadata System Software release 19.2.0,
flashCacheSize
is not a guaranteed reservation if the sum of theflashCacheSize
across all directives is more than the size of the flash cache. In this case, you can also specifyflashCacheMin
to define a guaranteed minimum quota.
Example 5-10 Configuring an Interdatabase Plan with Flash Cache Attributes
This example shows how to create an interdatabase plan with flash cache attributes.
In the example, the sales
and
test
databases are allocated an amount of
space in the flash cache by using the
flashCacheSize
parameter. But, the
databases cannot exceed the specified allocation, even if the flash
cache has free space.
The finance
and dev
databases use
flashCacheMin
for guaranteed minimum
quotas. These databases can also exceed the specified
flashCacheLimit
size when there is free
space in the flash cache.
ALTER IORMPLAN -
dbplan=((name=sales, share=8, flashCacheSize=10G), -
(name=finance, share=8, flashCacheLimit=10G, flashCacheMin=2G), -
(name=dev, share=2, flashCacheLimit=4G, flashCacheMin=1G), -
(name=test, share=1, limit=10, flashCacheSize=1G))
Example 5-11 Configuring an Interdatabase Plan with Flash Cache Attributes
Starting with Oracle Exadata System Software release 19.3.0, you can specify both flashCacheMin
and flashCacheSize
for the same target.
ALTER IORMPLAN -
dbplan=((name=sales, share=8, flashCacheMin=3G, flashCacheSize=10G), -
(name=finance, share=8, flashCacheLimit=10G, flashCacheMin=2G), -
(name=dev, share=2, flashCacheLimit=4G, flashCacheMin=1G), -
(name=test, share=1, limit=10, flashCacheSize=1G))
Parent topic: Administering the IORM Plan