[peterwwillis]

If you're keeping ALL of your user profile data in ACID-compliant databases you're probably doing it wrong.

Large modern websites store tons of information about a user which may not in any way be necessary to even keep for anything other than data mining, or perhaps preferences, click/hit tracking, etc. I can't see how such data is important in any way in regards to finances or trades, so why it couldn't be done on a much-less-resource-intense database solution I don't understand.

Moreover, the cascading effect of a database failure is made much worse by putting all your eggies in one basket and depending on this one cluster of databases to keep the whole ship afloat. In a good design scenario, much of the site should still keep operating even if the backend databases are timing out from load. For example, your cache layer (if not expired) should continue serving cached content/logins/etc. This may not be as useful for clients that sign in randomly or throughout the day, but for people who use the site frequently or stay logged in throughout the day their sessions should stay active in this scenario.

The content in the user profile which doesn't require ACID compliance could also be using caching and nosql/mysql/etc which would keep the apps working even longer in the event of an outage of a particular piece of technology. Because this technology doesn't require some of the more complicated requirements of Oracle RAC it may also be easier to recover/restore old data, again assuming this doesn't have a particular need for ACID.

[gaius]

I can't see how such data is important in any way in regards to finances or trades

Well, umm, it is. If you phone your broker and just chat about your cat, that will be taped too, and the tapes kept for 7 years.