DSC Mutability and Measurements

Problem statement:

Mis-match between transaction name set in DSC at beginning of trace and in transaction payloads later in trace. This is occurring at a high enough rate to indicate we cannot reliably sample based on trace.

Proposal:

Adjust the mutability of the DSC in an attempt to get a more accurate transaction name in the DSC of the overall trace, for sampling decisions to be more accurately reflect what users configure on product side.

To that end we would also like to gather metrics to further drive what types of changes, how often, and when they occur in the wild, so we can better determine when DSC should be “frozen”

Tasks:

Todo

In Progress

Done

• Experiment with metadata spec @AbhiPrasad https://github.com/getsentry/sentry-javascript/pull/5709
• Update transaction to record metadata around name changes https://github.com/getsentry/sentry-javascript/pull/5714
• Only record transaction name changes if data is different https://github.com/getsentry/sentry-javascript/pull/5728
• Track name changes in transaction class https://github.com/getsentry/sentry-javascript/pull/5723
• Update tracing sdk to record propagations https://github.com/getsentry/sentry-javascript/pull/5719
• Update node sdk to record propagations https://github.com/getsentry/sentry-javascript/pull/5720
• Update core event processing to record transaction name changes https://github.com/getsentry/sentry-javascript/pull/5722
• Update Relay to record new metadata measurements @jan-auer https://github.com/getsentry/relay/pull/1466
• make DSC mutable (unfreeze) only in JS (@lforst) https://github.com/getsentry/sentry-javascript/pull/5710
• Update TransactionNameChange interface to track prev source as per Relay changes https://github.com/getsentry/sentry-javascript/pull/5733

---

Diagram for visual learners (courtesy of @jan-auer):

[AbhiPrasad]

Final spec:

export interface TransactionInfo {
    source: TransactionSource;
    changes: TransactionNameChange[];
    propagations: number;
};

/**
 * Object representing metadata about when a transaction name was changed.
 */
export interface TransactionNameChange {
  /**
   * Unix timestamp when the name was changed. Same type as the start and
   * end timestamps of a transaction and span.
   */
  timestamp: number;

  /** Previous source used before transaction name change */
  source: TransactionSource;

  /** Number of propagations since start of transaction */
  propagations: number;
}

Implementation in Relay: https://github.com/getsentry/relay/pull/1466

[AbhiPrasad]

Feature has been released with https://github.com/getsentry/sentry-javascript/releases/tag/7.13.0