Am 14.04.2010, 14:45 Uhr, schrieb Hanno Schlichting <ha...@hannosch.eu>:
> Usually you will only loose the last transaction and not a days of > work. The Data.fs is an append-only file, with one transaction > appended after another. If there's a garbled or incomplete write, > you'll typically loose the last transaction. The ZODB is smart enough > to detect broken transactions and skip them on restart. > > I have witnessed one ZEO installation myself, where the physical > machine hosting the ZEO server restarted multiple times a day, over a > period of months. Nobody noticed for a long time, as the application > was accessible all the time and no data had been lost. Obviously this > wasn't a very write-intense application. But it still showed me how > stable the ZODB really is. Yes, I agree with your opinion in general. There's still a chance that broken transactions are written IIUC (see https://mail.zope.org/pipermail/zodb-dev/2004-July/007683.html ): >> Doesn't this mean that if the system suddenly crashes in the middle of >> os.fsync, the Data.fs on disk will contain an incomplete transaction, >> but >> the transaction status byte would claim that the transaction is >> complete. >> Wouldn't that be bad? > If that happened, perhaps. The chance exists because fsync does not work as advertised on many systems. On the systems where it seems to work, the slowdown is massive. So I am doubting the usefulness of using fsync in current ZODB at all. As your observations seem to hint, it's probably very unlikely to encounter this problem in practice. And I doubt Tim finally got Jim to pay him for a 48 hour pull-the-plug session :-) That's why I am not going to dig further into this and am satisfied with the current reliability. -Matthias _______________________________________________ For more information about ZODB, see the ZODB Wiki: http://www.zope.org/Wikis/ZODB/ ZODB-Dev mailing list - ZODB-Dev@zope.org https://mail.zope.org/mailman/listinfo/zodb-dev
