In the review for 49562 Thierry asked not to use "changelog.db" but some macros for the file name and the extension.
This sounds reasonable, but is not that trivial. The places the filename is used are in dbscan, in repl plugin and in the backend. The do not "know" of each other, no common include to define the name in one place.

Especially dbscan is "outside" the server cods, it even contains copies of functions to parse CL entries. And it is one place changelog.db is used, so changing it by using a defien doesn't make a real difference.

Remains the usage in bdb_layer and cl5_init. It could be done to independently define the NAME.EXTENSION in these places, and keep them consistent. But ".db" is BDB specific, it should no longer be seen in cl5_init after the backend isolation is completed.

My suggestion: for now leave it as it is, when doing the next backend step move it completely to the backend code and eventually get the filename "changelog" from the config entry "cn=changelog"