Hi All, if vacuum and merge are ran in parallel will vacuum delete files that are being committed ?

No

ok

How is it implemented? Is there also some threshold on the age of orphaned files?

To modify my no answer, it does appear if you vacuum 0 hours while another process has written but not committed files, you could lose data.

theoretically, if your merge takes longer than your data retention period - which is 7 days by default - they could conflict. but jobs taking days is extremely rare.