🚀 Meteor 3.5-beta: Change Streams & Performance improvements

mvogt22 · February 28, 2026, 10:31pm

italojs:

Change Streams Setup

To enable MongoDB optimizations, follow these steps:

Database Requirement: Ensure you are using a Replica Set or a Sharded Cluster. See the MongoDB documentation for more details.

Configuration: Add the following to your settings.json:
  {  
    "packages": {  
      "mongo": {  
        "reactivity": ["changeStreams", "oplog", "pooling"]  
        *// Meteor will try Change Streams first, then oplog,*  
        *// and if that doesn't work, fall back to pooling.*  
      }  
    }  
  }  

I think “pooling” should be “polling” - got an error when testing of Invalid Mongo reactivity method

wreiske · February 28, 2026, 11:10pm

Just had this exact problem!

Error: Invalid Mongo reactivity method in settings: pooling

This worked:

{
  "packages": {
    "mongo": {
      "reactivity": [
        "changeStreams",
        "oplog",
        "polling"
      ]
    }
  }
}

wreiske · March 1, 2026, 6:29am

I just shipped a major update to the meteor-react-tailwind-prettier-starter — bumping to Meteor 3.5-beta.3 and adding three production-quality real-time examples that showcase exactly what makes Meteor special.

https://todo-sample.meteorapp.com/

(sadly accounts-passwordless does not work on galaxy on --free plan. I’ll have to add a different way to login…)

nachocodoner · March 1, 2026, 6:57am

I’d love to see this package in action. I’m particularly excited about these experiments on new features missing in Meteor. Could you publish it?

It would be great to have the streaming capabilities in Meteor core at some point. Feel free to open a PR there if you like. For the core integration, we may get some feedback from the community or us so we can align on an interface that matches Meteor conventions, test coverage, and so on.

Anyway, publish as community package for now is fine. The core integration can come later, once the approach is tested by the community and we have clear guidance for integrating it into the core. As you prefer.

fredmaiaarantes · March 1, 2026, 12:22pm

This starter looks great, @wreiske!

What problem are you having with accounts-passwordless on the free plan? I don’t remember anything that would block it.

wreiske · March 1, 2026, 12:38pm

Thanks! Claud is good at making things pretty.

For some reason when trying to send the email, it causes an internal server error. I’m assuming emails are blocked to prevent spam.

It might be interesting to setup a fake mail server and when mail gets sent, users can go to inbox.meteorapp.com or something to read the mail. That would prevent abuse of outgoing mail but would still allow testing password less auth and other scenarios that require working email.

fredmaiaarantes · March 1, 2026, 2:19pm

I think you just need a mail provider and configure a MAIL_URL in your application, @wreiske.

wreiske · March 1, 2026, 7:21pm

Yeah, I was saying on meteor deploy --free it might be nice to have a “mock” email server that you can go check your mail. Even in local development, instead of just console logging out the email, it could use a nice real-time meteor inbox.

I might work on this. This is something supabase and other projects have with Mailpit - email & SMTP testing tool Mailpit - email & SMTP testing tool

harry97 · March 1, 2026, 8:57pm

github.com/meteor/meteor

[email] Warn if Accounts.emailTemplates.from isn't set

meteor:release-3.5 ← harryadel:fix/email-example

opened 07:10PM - 08 Dec 25 UTC

harryadel

+14 -0

## Problem When `Accounts.emailTemplates.from` is not configured, Meteor silen…tly uses the default: `Accounts Example <no-reply@example.com>` This causes emails to fail silently because: - example.com is a reserved domain - Most SMTP providers reject emails from this domain ## Solution We output a warning if from isn't explicitly configured. ## Related Issue While looking into this I also found out an interesting finding: [Issue #11640](https://github.com/meteor/meteor/issues/11640) reported that Email.send() fails silently when from is missing. [PR #11678](https://github.com/meteor/meteor/pull/11678) attempted to fix this by validating that from and to contain @: ```js if (!options.from?.includes('@')) { throw new Meteor.Error('invalid-mail-options', "Email options passed to send function must contain a valid 'from' address"); } if (!options.to?.includes('@')) { throw new Meteor.Error('invalid-mail-options', "Email options passed to send function must contain a valid 'to' address"); } ``` [Commit 20f7462](https://github.com/meteor/meteor/commit/20f74626080dd66dcaa216f22c34c8fdfeb11e1a) reverted PR #11678 because it "was causing problems and did not solve any issues." I'm unsure why this decision was taken. Maybe @filipenevola can shed some light.

mvogt22 · March 1, 2026, 9:29pm

Our ‘Event Loop Delay’ went from 97ms avg ‘(v3.4)’ to 18ms avg ‘(v3.5-beta.4)’ when using Change Streams.

V3.4

V3.5-beta.4

wreiske · March 1, 2026, 10:54pm

Just pushed an update that will send email to an inbox! BTW… does the --free plan allow testing change streams? https://todo-sample.meteorapp.com

italojs · March 2, 2026, 11:48am

it should support, i’ll double check it today

fixed in the root post

AMAZING! what observability tool are you using to mensure it?
[EDIT] : oh, just realized it’s SkySignal: Modern APM Built for Meteor 3.x

italojs · March 2, 2026, 12:18pm

agree 100% with nacho comment and add: please, open a forum topic only for it, let discuss better the usage, love it

grubba · March 2, 2026, 12:53pm

x-posting this:

I would love to see this in core at some point!

Having it be able to yield would be !

Is it open source? Could we see the package?

mvogt22 · March 2, 2026, 2:52pm

Better visual indicator of the performance benefits achieved with 3.5-beta.4, the red line is where it was deployed. Change Streams are going to be a scalability gamechanger for Meteor.

wreiske · March 3, 2026, 10:02pm

Wish me luck… about to migrate a mission critical real-time monitoring app we use to monitor our entire infrastructure. 1.11.1… it hammers CPU and oplog… i’ll let you know how change streams changes it!

This project uses Meteor 1.11.1, which isn't available on this platform. To
work with this app on all supported platforms, use
meteor update --release METEOR@3.4 to pin this app to the newest compatible
release.

Upgrading to 3.5-beta.4!!!

mvogt22 · March 4, 2026, 2:56pm

How is the upgrade going? Excited to hear your experience.

harry73 · March 4, 2026, 3:31pm

Hi,

I am currently testing 3.5-beta.4 and I have issues sur ObjectID.

I have collections with ObjectID fields. When I subscribe to a publication with these king of field, I can see the following in Meteor Dev Tools (DDP):

So, the application has errors.

With 3.4 or 3.5 / "mongo": { "reactivity": ["oplog", "polling"] }, I can see:

and everthing works well.

wreiske · March 6, 2026, 12:25am

It was originally a mixture of Blaze / Bootstrap / Ionic… Used meteor user-status to determine who was actively actually looking at the dashboard (bottom left avatars show activity in real-time like the rest of the dashboard)

Well, after 2 days of Opus 4.6 going at it and a little hand holding… it’s completely re-written in Typescript, React 19, TailwindCSS 4 and running smoothly! 1.11.1 to 3.5-beta.4 in 2 days!

This tool was my take on real time infrastructure monitoring before grafana was cool . Plus… it’s still more real-time than the “auto refresh” you get with tools like grafana/zabbix.

Another successful migration with this workflow:

Open VS code and start a new workspace
Go to File - > Add Folder to Workspace
Add your existing / old meteor project
git clone https://github.com/wreiske/meteor-react-tailwind-prettier-starter project-react somewhere on your machine
Go to File - > Add Folder to Workspace → select project-react
Open Copilot, make sure it’s in “Plan” mode and tell it that there are two projects in the workspace.

Here’s what I used:

There are two projects in the workspace.

statengine and statengine-react

statengine is an old Meteor 1 application that we need to rewrite into the new modern Meteor 3.4 stack inside of statengine-react, which is currently a “TODO example app” that is a “starter” template for React19, TailwindCSS 4, Typescript, etc.

Please come up with an extensive plan for how we can handle a complete migration and cleanup of the original statengine code base into the new format.

After a little while it will have a plan. review it and make any edits you think are required… This was my response:

OK. Let’s do it. Start the plan. Please make sure you put the entire plan into a markdown file and as you go through your plan, check off each item, so we know where we left off.

Also, i’d like to use luxon instead of date-fns.

And then hand hold it with a few “continue with the plan…” until it’s complete!

This workflow has allowed me to migrate several old projects with very little hand holding and my typical “format, lint, commit, push” prompt and copilot instructions to keep code DRY, KISS, etc…

YMMV!

Going to do some serious code review before pushing out to a test cluster node and then I’ll check our CPU / Memory / etc old vs new for a few days and see what improvements we get!

mvogt22 · March 6, 2026, 12:58am

Congrats! The new UI looks great.

Excited to hear what perf shows on 3.5