If you missed Andy Mendelsohn's keynote at E4 last week, you may not have heard the hubbub that surrounded one of his last slides (tweeted by Frits Hooogland here). The mention of the write-back enticed Kevin Closson to talk about the potential ramifications of such a feature. There's a lot of information on that slide to digest (what's a pluggable database? virtualization of database servers?), but I'm going to focus on the flash-based write-back cache. Note that this is not mentioning the "Exadata Smart Flash Log" featured introduced last year with the 18.104.22.168.0 cell patch, discussed by Guy Harrison recently. That feature sends writes to both flash and disk at the same time. In my experience, the disk wins on > 90% of those writes.
This is something larger than just sending writes to flash...an issue that Oracle has likely been working on for a few years. Kevin had mentioned in his post that he expected it to be a feature in the 12.2 release, possibly 12.1 of the database. Because Mendelsohn mentioned that there was a 12-month timeframe for these items, I expected it would occur with the release of the new version of the Oracle database, 12c. I've been doing some poking around in the latest Exadata patch notes and saw a couple of interesting bugs around a write-back cache on Exadata using flash. Bug 14143451 "Enhancement for ASM write-back flash cache resilvering support" and bug 14132953 "Enhanacement to add Write-back flash cache resilvering support" have both been added to the August 2012 bundle patch for 22.214.171.124 (MOS note #1393410.1). If you look at these bugs, you will see that they are currently listed as fixed in 126.96.36.199. The fact that the enhancement has been added to 188.8.131.52 interests me. It looks similar to the introduction of the Exadata smart flash log feature, introduced in the 184.108.40.206.0 Exadata storage server version, released October 2011. If you look through the Exadata bundle patches for 220.127.116.11, you'll see that it was introduced into the database code in bundle patch 9 (MOS note #1314319.1). That bundle patch was released in July 2011. Sound familiar? I wouldn't put it past Oracle to include the write-back cache through a new version of the storage server software.
This sounds like the kind of feature that Larry Ellison would be very happy to announce at Open World in October. We'll just have to wait and see what gets announced. I'll have another post in the next week or so guessing about what may get announced a month from now in San Francisco.