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On 23/02/16 15:45, Dennis Pallett wrote:
Hi all,
Is it possible to create a file system level backup of a running MonetDB database? What are the downsides of doing this?
For what it's worth, our databases are generally never updated outside of pre-fixed windows so only SELECT queries will be executed during any file system level backup.
Best regards, Dennis Pallett
At any point in time, the disk image of the database should be consistent. All committed transactions should be safe on disk. But MonetDB makes use of atomic file system operations to commit transaction s.
Since making a file system backup takes time, it could start before a transaction commits, and end after. If this happens, there cannot be any guarantees about the backup. Another potential for problems is when the server decides to do some database maintenance. Every once in a while, the write-ahead log (WAL) is cleaned up. It this happens during a file system backup, again there are no guarantees.
If neither of these events (transaction, WAL cleanup) happens during the backup, you're probably ok. But this is not something we can guarantee in any way, so to be sure of a proper backup, you should also create a sql-level backup (msqldump) in case the file system backup gives weird results after it is restored (which one of course hopes is never needed).
- -- Sjoerd Mullender