On Sat, Sep 04, 2010 at 02:42:40PM +0100, Greg Stark wrote: > On Fri, Sep 3, 2010 at 8:30 PM, Martijn van Oosterhout > <klep...@svana.org> wrote: > > > > rsync is not rocket science. All you need is for the receiving end to > > send a checksum for each block it has. The server side does the same > > checksum and for each block sends back "same" or "new data". > > Well rsync is closer to rocket science than that. It does rolling > checksums and can handle data being moved around, which vacuum does do > so it's probably worthwhile.
Not sure. When vacuum moves rows around the chance that it will move rows as a block and that the line pointers will be the same is practically nil. I don't think rsync will pick up on blocks the size of a typical row. Vacuum changes the headers so you never have a copied block. > *However* I tihnk you're all headed in the wrong direction here. I > don't think rsync is what anyone should be doing with their backups at > all. It still requires scanning through *all* your data even if you've > only changed a small percentage (which it seems is the use case you're > concerned about) and it results in corrupting your backup while the > rsync is in progress and having a window with no usable backup. You > could address that with rsync --compare-dest but then you're back to > needing space and i/o for whole backups every time even if you're only > changing small parts of the database. If you're working from a known good version of the database at some point, yes you are right you have more interesting options. If you don't you want something that will fix it. 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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