Proposal for performance priority labels

Current description

To help clarify priority of issues, from the perspective of their impact on availability and performance of GitLab.com.

Closes https://gitlab.com/gitlab-com/infrastructure/issues/1943

Original description

I do not think this is a priority right now, but it stems from https://gitlab.com/gitlab-com/www-gitlab-com/merge_requests/5373/diffs which I broke into smaller merge requests.

source/handbook/engineering/performance/index.html.md

@@ -159,3 +159,46 @@ revision, new revision, and ref (e.g. tag or branch) name.
 1. Sidekiq picks up the job from Redis and removes the job from the queue
 1. Sidekiq updates PostgreSQL
 1. Unicorn can now query PostgreSQL.
+
+### Availability and Performance Priority Labels
+{: #performance-labels}
+
+To clarify the priority of issues that relate to GitLab.com's availability and
+performance consider adding an _Availability and Performance Priority Label_,
+`~AP1` through `~AP3`. This is similar to what is in use in the Support and
+Security teams, they use `~SE` and `~SL` labels respectively to indicate
+priority.
+
+Use the following as a guideline to determine which Availability and Performance
+Priority label to use for bugs and feature proposals. Consider the _likelihood_
+and _urgency_  of the "scenario" that could result from this issue (not) being
+resolved.
+
+- **Urgency:**  _Examples_
+ - U1
+    - Outage likely within a month.
+    - Affects many team members and/or many GitLab.com users
+ - U2
+    - Outage likely within three months.
+    - Affects some team members and/or a few GitLab.com users
+ - U3
+    - Outage can happen, but not likely in next three months.
+    - Affects some team members but no GitLab.com users
+
+- **Impact:** _Examples_
+ - I1
+    - Outage of >= 25 minutes.
+    - Performance improvement (or avoiding degradation) of >= 100 ms expected.
+ - I2
+    - Outage of 5 - 25 minutes.
+    - Performance improvement (or avoiding degradation) of 10-100 ms expected.
+ - I3
+    - Outage of 0 - 5 minutes.
+    - Performance improvement (or avoiding degradation) of <= 10 ms expected.
+
+
+| **Urgency \ Impact**          | **I1 - High** | **I2 - Medium**  | **I3 - Low**   |
+|----------------------------|---------------|------------------|----------------|
+| **U1 - High**              | `AP1`         | `AP1`            | `AP2`          |
+| **U2 - Medium**            | `AP1`         | `AP2`            | `AP3`          |
+| **U3 - Low**               | `AP2`         | `AP3`            | `AP3`          |