Re: Backup Strategies

On 25/01/17 03:34, Stefan O'Rear wrote:

On Tue, Jan 24, 2017 at 1:32 PM, Martin Kersten wrote:

...

Never simply stop the server using e.g. a kill command.!!

Is MonetDB intended to survive a power failure, system crash, OOM condition, or other event which causes all database processes to terminate? (The existence of the "wal" implies the answer is yes)

The answer to this is indeed yes. However, disks sometimes lie to the operating system about the status of writes, so the OS might think a write to disk was successful when in fact the data is still in some cache internal to the disk. This falls outside the scope of MonetDB. And of course, bugs are always possible (and have been found and fixed in the past). But the intention is clear.

If so, then you could use a low-level atomic snapshot mechanism (LVM, zfs, btrfs support this) and then use rsync to copy the snapshot. After restoring the backup it will appear as if MonetDB simply crashed and should be able to recover from that.

rsync against a running database is highly unsafe because it copies different files at different times, but an OS-level snapshot will see a consistent version of all files in the dbfarm.

As long as the snapshot is indeed an atomic operation with respect to changes made to the file system by other processes (i.e. MonetDB), this is indeed a viable strategy.

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