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Above in this comment thread: ZODB Tips and Tricks » DirectoryStorage as performance booster? No. » reliability booster

cold failover and corruption

Posted by jens at 2005-07-22 04:14 PM
As far as corruption goes, I can only echo Tim Peters' words who says he has not seen a real ZODB corruption due to code bugs in a long time. Neither have I, even on the large-scale CMS systems I helped build and maintain at ZC. The only database that I have seen error messages in the log about (with no visible problems on the user side) is zope.org. This should have been solved by migrating the old zope.org software to the new one in a new ZODB during the migration, alas, it wasn't done that way...

I think you can get a pretty rapid failover by using repozo. It's not expensive to run against the database, so it is perfectly viable to run it e.g. once an hour to at least never lose more than 1 hours worth of changes.

Luck of the draw?

Posted by slinkp at 2005-07-24 07:28 PM
It's great that you guys haven't seen any data loss in the field in "a long time", I'm genuinely happy that most users have a good experience out-of-the-box. But as far as I know from the DirectoryStorage list, there have been ZERO reported cases of data loss with DS, ever. The problems I had with FS were very user-visible - whole folders went missing at the same time that we had massive POSKeyErrors, and they had to be laboriously restored from old backups. One of these occasions was likely caused by a long-since-fixed packing bug. The others, I have no idea whether the problems were ultimately caused by software issues, hardware issues (if so, there have never been any other visible problems on the same hardware, which has been up continuously for the past 40 months), or what. But after a while, you stop caring. It may not be totally rational, but it's kinda like if you drive a Ford and it careens off the road spontaneously on more than one occasion. Ford can show me reams of documents on how they've fixed the problem, or there's no proof the car was at fault, etc etc, but I still won't buy another one. Know what I mean?