Reading/Web/EventLogging best practices

Also see WMF wide EventLogging best practices: Extension:EventLogging/Guide

Schemas

 * Schemas in MobileFrontend should be prefixed with `MobileWeb`
 * The talk page should be edited with the `SchemaDoc` template. For example Schema_talk:MobileWebSearch

Sampling rate

 * When logging events that occur on every page view a sampling rate of 0.01%
 * If that schema is likely to track more than 1 event on a given page a more conservative measure of 0.005% is advised. When running the meta:SchemaMobileWebSectionUsage schema for example 1% was too high.
 * Be sure to check events for any newly deployed schema in grafana - above 40 events per second is typically a warning flag
 * When click tracking events on prominently used features, 1% is usually enough e.g. clicks to menu items or search usage (given that not all page views result in an event).

Consideration for experimental features in beta
If wanted you may want to consider a 100% sampling rate in beta. If so, please put this in the acceptance criteria for the task which implements the schema.

Use of session ids

 * Some events need to be linkable to other events, for example Schema:MobileWebSectionUsage records clicks to section headings in a given user session. This is usually done via a unique token that is generated once and used until the user closes the browser.
 * In some situations where workflows span multiple pages it may be necessary to persist such a token a little longer. When this is the case please ensure you minimise the duration the session is stored for.