Introducing Application Metrics: Track the signal, see the spike, jump to the trace

Summary

Sentry launched Application Metrics to capture application signals without pre-aggregating counters or discarding high-cardinality attributes like user IDs, project IDs, and regions. The system supports counters, distributions, and gauges within the existing SDK while linking each metric event directly to trace IDs for integrated debugging. Engineers demonstrated the feature by troubleshooting a Session Replay failure that triggered silently when sessions exceeded 1,000 video segments. By instrumenting distributions for replay event counts with project and replay attributes, the team isolated seven affected occurrences, navigated to connected traces and log lines, and reproduced the issue. Application Metrics comes enabled in recent SDK versions with 5GB included per plan.

Context

Sentry encountered a Session Replay issue where replays failed in certain browsers after loading more than 1,000 video segments without reliably generating error reports. Spans were sampled, risking missed outliers, and logs lacked structure, making it difficult to pinpoint affected users and reproduce the failure.

Approach / What changed

Sentry launched Application Metrics in its SDK to capture full metric events without pre-aggregation, preserving high-cardinality attributes like user ID, project ID, and trace ID. The feature provides Counter, Distribution, and Gauge metric types. Engineers instrumented replay.eventCount and replay.videoEventCount distributions with projectId and replayId attributes, enabling them to identify specific affected sessions, trace user actions via linked trace logs, and resolve the bug.

Takeaways

• Sentry Application Metrics stores full events instead of pre-aggregated counters, preserving high-cardinality fields such as user ID, region, and project ID.
• Metrics carry trace IDs, enabling developers to navigate directly from metric anomalies and spikes to associated traces, logs, and errors.
• The tool provides three primary metric types: Counter for totals and rates, Distribution for tracking spread across values, and Gauge for current point-in-time values.

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