I think we have raised a number of interesting issues here which require more deeper consideration. So I suggest to set this patch to Returned with feedback.
Btw., I just learned that copy_file_range() only works on files on the same device. So more arrangements will need to be made for that. > I have run some more tests on both macOS and Linux with ext4, and my> results > are that the bigger the flush distance, the better. Before we> made the adjustments for APFS, we had a flush size of 64kB, now it's 1MB> and 32MB on macOS. In my tests, I see 256MB as the best across both> platforms, and not flushing early at all is only minimally worse. Based on this, I suggest that we set the flush distance to 32MB on all platforms. Not only is it faster, it avoids having different settings on some platforms. -- Peter Eisentraut http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
