When I do a snapshot, that file is part of the snapshot. But are changes within the file kept as well? In other words, is it useful to have snapshots of a postgresql database server? If a database file uses 10% of the pool, and changes 20% between each snapshot, would the pool run out of space after 9 more snapshots? Or would the pool continue to have 90% free space? Or would only 70% or so free space? Thanks! -- http://www.glumbert.com/media/shift http://www.youtube.com/watch?v=tGvHNNOLnCk "This officer''s men seem to follow him merely out of idle curiosity." -- Sandhurst officer cadet evaluation. "Securing an environment of Windows platforms from abuse - external or internal - is akin to trying to install sprinklers in a fireworks factory where smoking on the job is permitted." -- Gene Spafford learn french: http://www.youtube.com/watch?v=30v_g83VHK4
On Thu, 12 Jul 2012, bofh wrote:> When I do a snapshot, that file is part of the snapshot. But are > changes within the file kept as well?Only the difference (at block level) between the snapshots is kept. If the changed data was changed 1000 times between the snapshots, then only the difference between the blocks at the exact time the snapshot was taken is preserved.> In other words, is it useful to have snapshots of a postgresql > database server? If a database file uses 10% of the pool, and changes > 20% between each snapshot, would the pool run out of space after 9 > more snapshots? Or would the pool continue to have 90% free space? > Or would only 70% or so free space?If it changes 20% between each snapshot then you would indeed soon run out of space unless older snapshots are destroyed. It is normally for only a tiny percentage of a filesystem''s data to change on a day by day basis. Bob -- Bob Friesenhahn bfriesen at simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
On Thu, Jul 12, 2012 at 7:32 PM, Bob Friesenhahn <bfriesen at simple.dallas.tx.us> wrote:> On Thu, 12 Jul 2012, bofh wrote: >> When I do a snapshot, that file is part of the snapshot. But are >> changes within the file kept as well? > > Only the difference (at block level) between the snapshots is kept. If the > changed data was changed 1000 times between the snapshots, then only the > difference between the blocks at the exact time the snapshot was taken is > preserved.Thanks! That helps me out! :) -- http://www.glumbert.com/media/shift http://www.youtube.com/watch?v=tGvHNNOLnCk "This officer''s men seem to follow him merely out of idle curiosity." -- Sandhurst officer cadet evaluation. "Securing an environment of Windows platforms from abuse - external or internal - is akin to trying to install sprinklers in a fireworks factory where smoking on the job is permitted." -- Gene Spafford learn french: http://www.youtube.com/watch?v=30v_g83VHK4