I have a large archive (close to a TB) so the Compact action takes 12-20 hours to complete.

I know I can safely pause/stop a Compact action and resume it later, but what would happen if I attempted to take another backup (recapture) before the Compact is restarted & completes? What about a Merge?

I'm assuming the archive won't be damaged, but would to Compact have to start all over from the beginning?

Steven J Gold wrote:... but what would happen if I attempted to take another backup (recapture) before the Compact is restarted & completes?

Just start it and find out.

Spoiler: the second action will simply wait for the compact to finish.

QRecall uses several layers of file access coordination so that no two actions are modifying the archive at the same time. (It's possible for multiple actions to read the archive at the same time; for example, you can run a recall action simultaneously with a verify or while the archive open in a browser.)

This works no matter how you run the actions. The scheduler will hold conflicting actions that are ready to run, but even if you start an action from the command line or another (networked) computer, the actions should handshake with one another so that only one is modifying the archive at a time.

Oops, I got distracted and forgot to answer the other half of the question.

The compact is incremental, because (most of) what it's doing is simply relocating records in the file so all of the records are physically adjacent to one another (no empty/unused space between those records). If you stop the compact you leave some records adjacent and others not. When you start it again, it will simply resume moving the non-adjacent records.

Empty space is created following actions that remove old data from the archive, most notably a merge.

A capture action only adds new records, so a capture won't create empty space or delete records.

So a capture won't have any material impact on the next compact action that runs because it never creates empty space or non-adjacent records.