Update 7-October-2011: the log write caching capability has been officially announced as “Exadata Smart Flash Log”. I saw a few Oracle product management slides at OpenWorld presentations; one slide deck online is here on slide 30. A sample graph is provided, showing how the peak response times drop significantly with the additional cache.
These peaks would correspond to the times when the controller RAM cache is full. Another feature of the cache is that it returns write success status to the database when either flash or disk controller acknowledge the write, meaning tat the flash memory functions as a type of upper bound to redo write latency.
Exadata storage server software version 188.8.131.52.0 (patch link) has just been released. The readme file (My Oracle Support login required) lists 218 different changes, but one in particular sticks out:
11781936 NEED SMART FLASH LOGGING OF RDBMS REDO
I have confirmed that this means that redo write caching is now available in Exadata storage servers. This can bring a huge boost to redo-intensive OLTP applications, especially when the small 512mb controller cache on the storage servers fills up during periods of heavy utilization.
Another change that may have impacts during an upgrade:
12563439 CELLMONITOR USER IS NOT RESTRICTED TO RUNNING CELLCLI
If you’re using the cellmonitor OS user run commands other than a plain cellcli, this may stop working on upgrade. This would happen if custom scripts were built to do additional monitoring that’s not part of cellcli.
The patch includes a new version of the OFED InfiniBand drivers, so those applying the patch to storage servers should also apply the included minimal pack to database servers as well, to keep driver versions consistent.