Follow-up from DBA review T246716#6324971, in order to avoid possible expensive DELETE queries and abuse of the platform, we should define a max number of subscriptions per user.
Do not allow the user to subscribe more than X devices for push-notifications
Is it possible to have expired subscriptions that wasn't purged?
See T259148 for a proposed implementation plan for handling expired subscriptions.
As for a specific max number of device subscriptions to allow per user, I would say that 10 seems like a reasonable maximum — relatively low, but still more than 99% of users will ever need. Of course we can always consider raising it if we get more than a few users complaining about it.
The specific maximum number of subscriptions per user should be defined in configuration, and it should probably be up to @sdkim what it is. In the meantime I'll pick this up to add the basic capability.
Change 619856 had a related patch set uploaded (by Mholloway; owner: Michael Holloway):
[mediawiki/extensions/Echo@master] Create and enforce a config setting for max subscriptions per user
Change 619856 merged by jenkins-bot:
[mediawiki/extensions/Echo@master] Create and enforce a config setting for max subscriptions per user
Change 621036 had a related patch set uploaded (by Mholloway; owner: Michael Holloway):
[operations/mediawiki-config@master] [BETA] EchoPush: Set max subscriptions per user to 10
Change 621036 merged by jenkins-bot:
[operations/mediawiki-config@master] [BETA] EchoPush: Set max subscriptions per user to 10