Did Domino 10 change NDX file names?

I've just upgraded a server from IBM Domino 9.0.1 to Domino 10.0.1, and am having some trouble with NDX files (view indexes stored outside databases).

I tested some custom app functionality after the upgrade, and found that code which used views sometimes produced the error message "Attempt to Reopen an Open Container".

To resolve the error, I ran the server command load updall -R to rebuild all used views. After that completed, I found there are now two NDX files for every NIFNSF-enabled database.

For each NSF, the older NDX file was last updated before the upgrade, and is named to match the NSF base filename with the extension replaced by "NDX". The newer NDX is updated within the last 15 minutes, and named like the NSF base filename, plus "_nsf", then the "NDX" extension.
E.g. A database file "Arc2001.nsf" has both "Arc2001.ndx" (older) and "Arc2001_nsf.ndx" (newer).

So the main question is: Did the default name of NDX files change with Domino 10?
And closely related: Can I safely delete the older NDX files?

In case it matters, the Domino upgrade path wasn't simple, since I moved to a new OS and virtual server, and changed from 32-bit Domino to 64-bit, all at the same time.

I first copied all Domino install and data files from the old Windows Server 2012 to the new Windows Server 2019, then removed native binaries (EXE, DLL, and some extensions I know are created by Visual Studio) in case there could be any issue with the change from 32-bit to 64-bit, then installed Domino 10.0.1 over the copied files. I had to modify some INI files to change host names and IP addresses, and was then able to start and use Domino 10.0.1 with no trouble aside from what I've described above.

Solution 1:

With no other answers (as yet) and with my not being able to find official information about the NDX filename format, I've done some testing to answer this to my satisfaction.

On the Domino 10.0.1 server, if I enable NIFNSF on a database that previously had it disabled, the NDX filename is formatted just like the new NDX files that appeared after rebuilding views, i.e. with "_nsf" before the extension.

Also if I stop Domino, remove all the old NDX files that I copied from the 9 server, and start Domino again, those files don't reappear and I haven't seen any error messages or other problems.

Conclusion: The NDX filename format changed at some point in Domino 10.0.0, 10.0.1, or one of the fix packs for those versions, and NDX files using the old name-format can be safely deleted.