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Tuesday, July 26, 2016

Database Smart Flash Cache

If your database is running on Solaris or Oracle Linux, you can optionally add another memory component: Database Smart Flash Cache. Database Smart Flash Cache is an extension of the SGA-resident buffer cache, providing a level 2 cache for database blocks. It can improve response time and overall throughput for both read-intensive online transaction processing (OLTP) workloads and ad hoc queries and bulk data modifications in a data warehouse environment. Database Smart Flash Cache resides on one or more flash disk devices, which are solid state storage devices that use flash memory. Database Smart Flash Cache is typically more economical than additional main memory, and is an order of magnitude faster than disk drives.




Consider adding Database Smart Flash Cache when all of the following are true:
  • Your database is running on the Solaris or Oracle Linux operating systems. Database Smart Flash Cache is supported on these operating systems only.
  • The Buffer Pool Advisory section of your Automatic Workload Repository (AWR) report or STATSPACK report indicates that doubling the size of the buffer cache would be beneficial.
  • db file sequential read is a top wait event.
  • You have spare CPU.
Sizing Database Smart Flash Cache

As a general rule, size Database Smart Flash Cache to be between 2 times and 10 times the size of the buffer cache. Any multiplier less than two would not provide any benefit. If you are using automatic shared memory management, make Database Smart Flash Cache between 2 times and 10 times the size of SGA_TARGET. Using 80% of the size of SGA_TARGET instead of the full size would also suffice for this calculation.



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