> On Aug 19, 2015, at 5:49 PM, tvdien@... [firebird-support] <firebird-support@yahoogroups.com> wrote:
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> I believe it is generally safe to have multiple simultaneously running instances of Gbak backing up the same server, when all of them read data from within their own transaction.

Right. Gbak is just another application. It generates its own BLR, which is unusual, but actually easier than generating SQL, if you happen to be a program. If it were a modern program, it would generate dynamic SQL. It's also pretty smart about dependencies between system table elements. However, there is not magic. A Gbak backup is just a read-only application, like any other.

> Is that any different when Gbak is not supplied with the argument to skip garbage collection?

All applications that read the database do garbage collection by default. Coopertive garbage collection and the garbage collect thread all work together all the time.

> Does that put either the backup file or (worse) the database itself at risk of corruption? Perhaps someone can explain how this would work out under the hood.

No magic, except the normal magic of MVCC.

My question to you is why run multiple simultaneous backups?

Good luck,

Ann

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