1498166 - Implement multi-store for histograms

Status: RESOLVED FIXED

(Toolkit :: Telemetry, enhancement, P1)

Description

[Jan-Erik Rediger [:janerik]]

Histograms need to gain functionality to record into multiple stores.

Comment 1

[Jan-Erik Rediger [:janerik]]

Attachment: Bug 1498166 - Use fully-qualified name for histogram storage

This is a preparation for the following introduction of a new wrapper
type by that name, making it more explicit which class we're handling

Comment 2

[Jan-Erik Rediger [:janerik]]

Attachment: Bug 1498166 - Add multi-storage to plain histograms

This introduces a new wrapper `Histogram` that keeps track of the multiple stores a histogram can be in.
Histograms are stored in a hash table, indexed by the name of the store.

It has one optimization to support the majority of cases: a single `main` store.
For that it stores a direct pointer to the underlying base::Histogram and skips populating the map.
This saves an indirection and memory overhead of actually placing it into the hash table.

For now a snapshot only ever returns data from the main store.
Clearing a snapshot only clears the main store.
(This will both change in a follow-up)

Depends on D11904

Comment 3

[Jan-Erik Rediger [:janerik]]

Attachment: Bug 1498166 - Add multi-storage to keyed histograms

This extendes the `KeyedHistogram` to keep track of the multiple stores a histogram can be in.
Keyed histograms are stored in a hash table, indexed by the name of the store.

It has one optimization to support the majority of cases: a single `main` store.
For that it stores a direct pointer to a map from keys to the underlying base::Histogram and skips populating the map.
This saves an indirection and memory overhead of actually placing it into a second hash table.

For now a snapshot only ever returns data from the main store.
Clearing a snapshot only clears the main store.
Getting the keys of a keyed histogram will only get it from the main store.
(This will change in a follow-up)

Depends on D11905

Comment 4

[Jan-Erik Rediger [:janerik]]

Attachment: Bug 1498166 - Test storing into multiple stores (and snapshotting main store)

For now we test that storing still works and the main store is still accessed for snapshots and clearing.

Depends on D11906

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/b362f996a039
Use fully-qualified name for histogram storage r=chutten
https://hg.mozilla.org/integration/autoland/rev/137130a36a22
Add multi-storage to plain histograms r=chutten
https://hg.mozilla.org/integration/autoland/rev/544d3ecf27ab
Add multi-storage to keyed histograms r=chutten
https://hg.mozilla.org/integration/autoland/rev/ed977fa7caf8
Test storing into multiple stores (and snapshotting main store) r=chutten

Comment 6

[Cosmin Sabou [:CosminS]]

https://hg.mozilla.org/mozilla-central/rev/b362f996a039
https://hg.mozilla.org/mozilla-central/rev/137130a36a22
https://hg.mozilla.org/mozilla-central/rev/544d3ecf27ab
https://hg.mozilla.org/mozilla-central/rev/ed977fa7caf8