On Tue, 3 Jul 2007 13:15:06 -0400 "Xin Zhao" <uszhaoxin@xxxxxxxxx> wrote: > OK. From discussion above, can we reach a conclusion: from the > application perspective, it is very hard, if not impossible, to take a > transactional consistent snapshot without the help from applications? You definitely need help from the applications. They define what a transaction is. > > Chris, you mentioned that "Many different applications support some > form of pausing in order to facilitate live backups. " Can you provide > some examples? I mean popular apps. Oracle, db2, mysql, ldap, postgres, sleepycat databases...just search for online backup and most programs that involve something transactional have a way to do it. > > Finally, if we back up a little bit, say, we don't care the > transaction level consistency ( a transaction that open/close many > times), but we want a open/close consistency in snapshots. That is, a > file in a snapshot must be in a single version, but it can be in a > middle state of a transaction. Can we do that? Pausing apps itself > does not solve this problem, because a file could be already opened > and in the middle of write. As I mentioned earlier, some systems can > backup old data every time new data is written, but I suspect that > this will impact the system performance quite a bit. Any idea about > that? > This depends on the transaction engine in your filesystem. None of the existing linux filesystems have a way to start a transaction when the file opens and finish it when the file closes, or a way to roll back individual operations that have happened inside a given transaction. It certainly could be done, but it would also introduce a great deal of complexity to the FS. -chris - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
