Should I just go ahead with it? Am happy to.
The migration isn't that fraught, because if it goes wrong we'll still have the original data files and can revert to the Sqlite system. The main risks are a) not capturing stats correctly after the migration, and b) not importing the old stats correctly. I've tested it and can't find any errors.
On wsexport-test, I created a number of pdf/epubs/etc. and saw the statistics rise as appropriate.
I saw no suspect messages in the error logs.
Installing on my local VM following the new install instructions went smoothly.
There was a bug where the statistics for the final day of a month were not being displayed (https://github.com/wsexport/tool/pull/196). This is now fixed on wsexport-test (but not production yet).
I believe when importing the old statistics from sqlite we ignore any duplicates of rows which have the same language, ebook title and timestamp.
There are a small number of these duplicates in the old sqlite database, presumably where the same ebook was generated twice within a second. Or, perhaps the duplicates are a bug in our old statistics collection code (I have not investigated this).
On production, in May, June and July we are missing about 800-1000 per month from a total of 75000-90000 per month.