Oracle 11g Release 2 includes a feature called flash_cache, a table and index argument that resembles the assignment of high use objects to the KEEP pool.
However, unlike the KEEP pool which uses volatile RAM disk, the flash_cache is used for tertiary storage on solid-state disk (SSD). On Oracle, SSD is up to 600 times faster than platter disks, and at only $2,000.00 per gigabyte, SSD technology is going to replace platter disks for most systems by 2015. In fact, the 2009 Sun servers have on-board SSD flash memory.
The Oracle documentation suggests enabling the flash_cache when the data buffer advisor suggests that Oracle wants more RAM, which is very common, when the system is disk I/O bound and when the system has spare CPU cycles.
They mention CPU because moving to solid-state flash storage removes disk I/O but changes the workload bottleneck to CPU in many cases.
In other words, flash_cache is for every system that is not already running an SSD back end! It should be considered if:
* 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.
Of course, many Oracle shops have been running solid-state disks for many years now, so it is not really a new technology. In traditional SSD, the SSD looks just like a platter disk, except that the I/O can be hundreds of times faster!
See below for expert Oracle flash_cache tips:
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Oracle flash_cache tips
