Tips on sending batch notifications to a large group of users at once?
Hi team, for context - I'm storing user ExpoPushTokens in my users table in Convex. I was reading some of the docs on cron jobs in Convex and was wondering what the recommended approach would be to send daily notifications to a large group of users at once (doesn't have to be at exactly the same time). I was thinking I could make a call to fetch the users table (though I'd probably wanna do this in a paginated manner so I don't fetch too many items at once), get the Expo push tokens that way, and then make batched calls to the Expo service using an internal action.
Is this the recommended approach for a use case like this?
10 Replies
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Thank you!
Just checking that you've seen https://github.com/get-convex/expo-push-notifications
Paginating sounds good here (probably by something like
_creationTime so you can make sure you get all the users even if the data changes between fetching pages). Sounds like you already know that Expo has a batch API for sending push notifications which you want to use.
One way to do this is with a mutation that fetches a page of data, kicks off the internal action, and then schedules itself to run again with a cursorGitHub
GitHub - get-convex/expo-push-notifications
Contribute to get-convex/expo-push-notifications development by creating an account on GitHub.
@sshader yep! saw this but since I already store the push tokens on the user side, decided I probably didn’t need to use the convex component. was going down the route of defining a “use node” internal action that used the expo-server-sdk for sending notifications in batches of 100 until users have been exhausted
was going to run this action in a cron that ran daily - are scheduled functions necessary here or can the cron that loops over users in batches suffice? is there a time limit to actions/crons?
The cron would kick off once per day, and while you could have it be a single long running action that pages through users, there's risk of it timing out. Having the action fetch a page, send notifications, and then reschedule itself with the cursor for the next page is a sturdier approach.
Makes sense to not use the component if you already have tokens stored (but also migrating shouldn't be too hard if you ever want to), but it might be a good source of inspiration for sending batched notifications (I don't think I used
expo-server-sdk in the component and just hit their API with a fetch, but idk what niceties the sdk provides)
There aren't limits specific to crons, but an action can run at most 10 minutes. As erquhart said, if you do self scheduling functions, you'll never have to worry about the 10 min action limit. Yet another approach is to do self scheduling mutations, which load a batch, schedule an internal action to send the notifications, then schedules itself. Mutations get automatically and safely retried on failure, so you have a better shot of all your notifications getting delivered (vs. if one of your actions fails in one of the first few batches, you might fail to handle all the rest of the data)@pez I know that might not be the answer you are looking for, but most likely you could do that more easily OneSignal (an alternative to expo push notif), that has a RN SDK.
Basically:
1. Every user in your app is registered thanks to the onesignal sdk
2. Every day you launch a cron on convex that calls the onesignal api
3. OneSignal handles for you push messaging ALL your users in one shot
@erquhart @sshader these are awesome suggestions!! thanks for the help here. Will try scheduling actions/mutations
@sshader so you’re saying call a mutation which itself calls an internal action to send notifs in batches of 100. then let the mutation schedule itself again with the next page of users?
would definitely want to optimize for reliable delivery, so mutations might be the move here
I'd enqueue these batches in a workpool ( https://www.convex.dev/components/workpool ) for reliable retries etc.
Convex
Workpool
Workpools give critical tasks priority by organizing async operations into separate, customizable queues.
and to rate limit this background work in a systematic way
@jamwt super cool stuff. will give it a try!