We have instructions telling people to run the bg job 'populate_stats_process_rooms', but it is a no-op

[anoadragon453]

Description

In this delta file we converted populate_stats_process_rooms to a no-op and created populate_stats_process_rooms_2 in order to get around some edge cases with older Synapse versions.

It seems that this was not necessary, and we could've kept the same name and simply purged the progress of and restarted background job in the delta file instead.

The chosen solution has problems as there are places that we tell people to use populate_stats_process_rooms to fix issues. These instructions now simply do nothing as the bg job is a no-op.

A DELETE was used to solve a similar problem in another delta file:

synapse/synapse/storage/databases/main/schema/delta/56/stats_separated.sql

Line 31 in a7bdf98

DELETE FROM background_updates WHERE update_name IN (

The delta file should be updated to sort out this mess.

[reivilibre]

It seems to me that one could add a new delta and UPDATE _2 jobs to the old name (and of course modify the code to make the original name not a NOP).

(Fixing the existing delta file is not necessarily good as it has already gone out, and someone may be half-way through running the job when they upgrade to the version where we back out the _2 job)

[anoadragon453]

@reivilibre I was planning to delete the progress again, but you're right in that I think we could keep the user's existing progress by just creating a new delta file. Thanks :)

[anoadragon453]

Oh, but we'll need to delete the progress anyways to cover the edge cases laid out in the original problematic delta file...

[reivilibre]

You wouldn't need to delete the progress made by a _2 job, right?

i.e. a delta which:

• deletes populate_stats_process_rooms
• renames populate_stats_process_rooms_2 to populate_stats_process_rooms

should do as intended?

[anoadragon453]

@reivilibre After running through the possible upgrade paths through the notable versions (<=v1.18.0, v1.19.0, and $next_version), this suggestion seems to work in all cases. Thank you!