Update user_definitions.md

handbook/ops/bizops/user_definitions.md

@@ -30,3 +30,23 @@ We track the following categories in pings for each month. The explanations are
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 | DAU/MAU | The ratio of average DAUs over a month to the number of MAUs in the corresponding month. If the ratio is 0.4 or 40%, the average user used Sourcegraph 12 days per month (30 days * .4 = 12). |
 | DAU/WAU | The ratio of average DAUs over a week to the number of WAUs in the corresponding week. If the ratio is 0.4 or 40%, the average user used Sourcegraph 2.8 days per week (7 days * .4 = 2.8).   |
+
+# How are users calculated in the app?
+
+
+Our metrics infrastructure (Looker, Amplitude) gets user counts from our event_logs database.
+
+### On-Prem Instances
+In each ping, instances will send a site_activity.DAUs, site_activity.WAUs, and site_activity.MAUs field which represent daily, weekly, and monthly user counts on an instance. These numbers are taken from the `event_logs` table of the instance, and count the number of distinct user IDs that executed any action on the instance in a given time period. See the [`activeUsers` function](https://sourcegraph.com/search?q=context:global+repo:%5Egithub%5C.com/sourcegraph/sourcegraph%24%407eeeb9b+func+activeUsers&patternType=literal) for the implementation and SQL query.
+
+### Sourcegraph Cloud
+
+For Sourcegraph Cloud, we use the same method for calculating user counts, pulling from the Sourcegraph Cloud database. However, for Cloud, we track unauthed users using their `anonymous_user_id`. This is a separate column which contains an anonymous ID, which is stored in a cookie for users that visit Sourcegraph.com. Therefore, for all charts that track Cloud active users, this includes unauthenticated users. 
+
+There are shortcomings to this. For one, when a user converts into an authed user, their events conducted with their anonymous user ID are still in the DB, so we would count two different users being active rather than a single user.For analytics purposes in Amplitude, this is also not ideal because we are not able to connect the actions of a user before and after they've converted.
+
+### In-app site admin usage stas page
+
+This is a known issue. In the site admin panel, we have a Usage stats page that displays number of MAUs. This pulls data from Redis, which gets populated by our `usagestatsdeprecated` package. This was an old way of collecting data, and is not reliable. This has been raised, and will be fixed to use the `event_logs` table. 
+
+