On Sun, Sep 12, 2010 at 12:18:10PM +0200, J. Roeleveld wrote: > How can you ensure the snapshot is in a consistent state if the server is > running? > > If a snapshot is taken between 2 updates in a single transaction, only half > of > this transaction is included in the snapshot. > I would never take an LVM (or similar) snapshot of an application that can't > be paused in a way to provide a consistent filesystem.
That's the trick, the filesystem is always in a consistant state, otherwise how could a database survive a power failure? The trick is WAL, which ensure that changes are logged consistantly and replays them if the database crashes. If you take a snapshot the database will simply startup and replay the log as if the machine crashed at the point. All committed transactions appears anything uncommitted vanishes. Have a nice day, -- Martijn van Oosterhout <klep...@svana.org> http://svana.org/kleptog/ > Patriotism is when love of your own people comes first; nationalism, > when hate for people other than your own comes first. > - Charles de Gaulle
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