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+title: "This Week in Glean: Differences"
+published_date: "2019-11-29 11:37:00 +0100"
+layout: post.liquid
+data:
+  route: blog
+---
+
+(“This Week in Glean” is a series of blog posts that the Glean Team at Mozilla is using to try to communicate better about our work. They could be release notes, documentation, hopes, dreams, or whatever: so long as it is inspired by Glean. You can find an [index of all TWiG posts online](https://mozilla.github.io/glean/book/appendix/twig.html))
+
+Last week's blog post: [This Week in Glean: Glean in Private](https://chuttenblog.wordpress.com/2019/11/22/this-week-in-glean-glean-in-private/) by chutten.
+
+---
+
+Currently my team is responsible for the Telemetry framework inside Firefox on Desktop and also [Glean](https://github.com/mozilla/glean), targeting our mobile products.
+We're working on bringing the Glean experience to Firefox on Desktop, but in the meantime [Telemetry](https://firefox-source-docs.mozilla.org/toolkit/components/telemetry/index.html) is what we have,
+need to support and sometimes implement new features on.
+
+One of these features is a new ping (or better a change in a ping), that we now want to support across all our products.
+I'm speaking of the [`deletion-request` ping](https://firefox-source-docs.mozilla.org/toolkit/components/telemetry/data/deletion-request-ping.html) here.
+When a user opts out of Telemetry we take this as a signal to also delete associated data from our pipeline.
+
+Implementation in Firefox Desktop was merely renaming an existing ping that is triggered when the user disables "Data Collection and Use" (`about:preferences` -> Privacy & Security). It contains no additional data.
+Implementation in Glean was not much harder either. Glean already supports [custom pings](https://mozilla.github.io/glean/book/user/pings/custom.html): Pings that can be defined and send by the application using Glean.
+Glean's internal pings follow the same pattern, they are just pre-defined.
+The biggest difference?
+
+It's called `deletion_request` ping instead.
+
+Glean also enforces the payload schema of pings.
+Glean itself controls portion of the data, including a sequence number, date field
+and a bit of metadata about the application its running in (see [the ping sections](https://mozilla.github.io/glean/book/user/pings/index.html#ping-sections)).
+The rest of the payload consists of [metrics](https://mozilla.github.io/glean/book/user/metrics/index.html) as defined by users of Glean.
+While implementing the new ping I stumbled upon another small detail of Glean: Pings won't be sent out if they would not contain any metrics.
+And our new ping by choice should not contain any metric!
+
+We don't want to change this for other pings, so I had to introduce a new flag now:
+`sendIfEmpty` ([PR #139](https://github.com/mozilla/glean_parser/pull/139)).
+
+That way we can allow the `deletion_request` ping to be sent without any metrics in there, only containing the basic information.
+
+The implementation of the new ping is now done and currently waiting for data review ([PR #526](https://github.com/mozilla/glean/pull/526)).
+I hope to land this early next week.