The SDKs behave differently when it comes to session updates for dropped events.

There are four ways of dropping an event:

• sampleRate
• ignoredExceptionForTypes, also called ignore_errors
• eventProcessor (scoped and global)
• beforeSend

python

In python all of them drop the event before updating the session. The order of execution in python is:

• ignore_errors
• sampleRate
• eventProcessor (scoped) - called error_processors
• eventProcessor (global) - called event_processors
• beforeSend
• --- session update --- never reached for dropped events

Java

The behaviour and order in Java differs from the python implementation:

• eventProcessor (scoped) - early return on drop
• eventProcessor (global) - event set to null, creates and sends envelope if attachments are available, no session update counted or sent
• --- session update --- note: this update may not make it to the server immediately
• sampleRate - event set to null, sends attachments and session update
• ignoredExceptionForTypes - semi early return, session has already been updated but is not being sent immediately
• beforeSend - event set to null, sends attachments and session update

Link to issue in sentry-java: getsentry/sentry-java#1916

JS

The JS SDK does not update the session in any of the cases. The order is:

• sampleRate
• eventProcessor - I'm not sure on the order of global vs scoped here: https://github.com/getsentry/sentry-javascript/blob/249302aa8fb30648528928a3629a7ea2349de62d/packages/hub/src/scope.ts#L441 My guess would be: global happens before scoped.
• beforeSend
• --- session update ---

Note: ignoredExceptionForTypes doesn't seem to be available in JS.

Other SDKs

Cocoa (thanks @philipphofmann), native (thanks @Swatinem) and Rust (thanks @Swatinem) update the session

Desired behaviour / suggestions

• Current implementation in python as a basis (i.e. don't update session for dropped events)
• @bruno-garcia suggested, we update the session for sampleRate as the session should reflect reality not dropped data - If it wasn't an error, don't count it.
• @untitaker on whether a dropped event should update the session:
  ** beforeSend - We don't really know; usecases are overloaded
  ** sampleRate - SDK option: IMO yes
  ** ignoredExceptionForTypes - option: IMO no
  ** eventProcessor - option: IMO no, but it depends who can set an event processor. is that private API? do we know what it's used for?
• @untitaker suggested we check ignoredExceptionForTypes before sampleRate

Questions:

• Seems there is some aggreement on only updating the session for sampleRate drops and nothing else. Should we change the implementations to match this?
• Do we want to align filter order across SDKs?