1934095 - Extend GIFFT (quietly) to support mirroring to histograms with `kind: boolean` and `kind: count`

Status: RESOLVED FIXED

(Toolkit :: Telemetry, enhancement, P1)

Description

[Chris H-C :chutten]

If we hope to remove Legacy Telemetry's Histogram APIs and replace their use with Glean APIs, we need to be able to mirror to existing histogram types. Two as-yet-unsupported-by-GIFFT histogram types are kind: boolean (counts of truths and falsehoods) and kind: count (a simple count, which has been forbidden in favour of uint scalars for about eight years (bug 1278531), but nevertheless persists)

The way that Glean would expect you to encode "Histogram with kind: boolean" data would probably be labeled_counter with two fixed labels: one describing the true case and one describing the false case (like for APPLICATION_REPUTATION_SHOULD_BLOCK it could be should_block and shouldnt_block. Just pick something more descriptive than true and `false). This allows for more cases cropping up in the future.

The way that Glean would expect you to encode "Histogram with kind: count" data would definitely be a counter.

This bug is about designing and implementing and testing the ability to map from labeled_counter to Histograms with kind: boolean and from counter to Histograms with kind: counter. We will not be documenting these transforms as possible in the user-facing GIFFT docs because we don't want people adding new Histograms with kind: boolean or kind: counter. The former should be keyed scalars with kind: uint, and the latter non-keyed scalars with kind: uint.

Comment 1

[Chris H-C :chutten]

Attachment: Bug 1934095 - Support mirroring from counter metrics to count histograms r?TravisLong

Secret menu: It is possible to mirror from a counter metric to a Histogram
probe with kind "count" if you prefix the mirror's HistogramID with "h#".

Comment 2

[Chris H-C :chutten]

Attachment: Bug 1934095 - Support mirroring specific labeled_counter metric to histograms of kind: boolean r?TravisLong,brosa

Not only does it have to be a labeled_counter,
not only does it have to prepend its telemetry_mirror property with h#,
it also has to have a labels: ["false", "true"] (in that order),
and it'll assert on debug builds if you use it wrong.

Comment 3

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/3c665d65abf4
Support mirroring from counter metrics to count histograms r=TravisLong
https://hg.mozilla.org/integration/autoland/rev/beab9166b295
Support mirroring specific labeled_counter metric to histograms of kind: boolean r=TravisLong

Comment 4

[pstanciu]

https://hg.mozilla.org/mozilla-central/rev/3c665d65abf4
https://hg.mozilla.org/mozilla-central/rev/beab9166b295