2020962 - Implement Session Lifecycle and State Management

Status: RESOLVED FIXED

(Data Platform and Tools :: Glean: SDK, task, P1)

Description

[Travis Long [:travis_]]

Implement the session state machine in the SDK, including:

• Lifecycle modes (AUTO default, LIFECYCLE, MANUAL)
• Handling of active/inactive signals
• Inactivity timeout behavior
• Cold restart handling
• Session start/end transitions

Includes generation and management of:

• session_id (UUIDv4)
• session_seq
• event_seq

Modify event recording to:

• Attach structured session metadata to in-session events
• Emit session_start and session_end synthetic events
• Include effective session sample rate in metadata
• Update payload schema and documentation accordingly.

Implement:

• Deterministic session sampling decision at session start
• Gating of in-session telemetry when sampled out
• Runtime session_sample_rate configuration (init + remote override)
• out_of_session exemption behavior
• Diagnostic metric (glean.sessions_seen) for observability

Includes tests for sampling semantics and metadata correctness.

Comment 1

[Travis Long [:travis_]]

Assuming sequential execution and ~16 weeks total duration starting March 16, 2026, here are the expected completion dates:

Step 1: Design Finalization & Architecture Approval (3 weeks)
Expected completion: April 6, 2026

Step 2: SDK/parser/pipeline implementation (estimate 6-8 weeks)

• Core Session State Machine Implementation
• Per-Session Sampling & Diagnostics
• Payload Schema & Metadata Integration
  Expected completion: May 18, 2026

Step 3: Performance & Payload Impact Validation (2 weeks)
Includes Bug 2020967
Expected completion: June 8, 2026

Step 4: ETL Modeling & Pilot Rollout (3 weeks)
Includes Bug 2020968, Bug 2020970
Expected completion: June 30, 2026

Overall projected completion: July 6, 2026
(Flows will follow in a separate, later phase: Bug 2020971)

Comment 2

[Travis Long [:travis_]]

Attachment: [mozilla/glean] Bug2020962 sessions (#3438Edit title)

Comment 4

[Travis Long [:travis_]]

Attachment: [mozilla/glean_parser] Bug2020962 session impl (#840Edit title)

glean_parser changes

Comment 5

[Travis Long [:travis_]]

Attachment: [mozilla-services/mozilla-pipeline-schemas] Bug 2020962 - Add session metadata to Glean events (#869Edit title)

pipeline schema updates PR

Comment 6

[Travis Long [:travis_]]

I originally had the wrong bug for the schema updates, they are now linked here properly

Comment 7

[Travis Long [:travis_]]

Pipeline schema PR is queued for review, which usually doesn't take long. After that lands I will need to update the copy of the schema in the SDK PR, then it and the glean_parser PRs can land. Then releases cut for Glean and glean_parser, vendoring, and collecting data for validation. I expect to get this stuff landed and released/vendored next week.

Comment 8

[Travis Long [:travis_]]

All PRs are reviewed except the pipeline schema additions. I'll push for review on it as it needs to land first, then the other two PRs updated with the schema from the pipeline generator and then they can land too.

After landing, it will take about a week to begin to have enough data to start validating the session metadata, then a day or two to complete the initial validation. Validation will continue through vendoring into consuming applications to ensure everything is working as expected.

Once validation is completed, then work on Flow-ids and the associated metadata will begin.

Comment 9

[Travis Long [:travis_]]

Everything has landed. Tomorrow I will work on cutting a Glean release and then we will be collecting data for the next steps of validation, and checking the payload size impact, etc.

Closing this as FIXED and moving onto the next bugs in the tree