Handling "2 items dropped from union(s)" Warning in Grafana

Grafana Prometheus
16

Recommendations

  • Understand the Warning: Recognize that the warning about “items dropped from union(s)” is due to mismatched label sets in time series data when performing mathematical operations.

  • Align Timestamps: Ensure that the timestamps of the series you are trying to operate on are aligned to avoid unnecessary warnings.

  • Use PromQL for Calculations: Consider performing calculations at the PromQL level to avoid issues with Grafana’s expression handling.

  • Resample Data: If necessary, use resampling techniques to align data points before performing operations.

  • Label Matching: Use PromQL’s on() operator to specify which labels should be matched during operations, or use sum() to ensure label sets are consistent.

Summary

The thread discusses a warning encountered after upgrading to Grafana v10.2.3, where users see “2 items dropped from union(s)” when performing mathematical operations on time series data. This warning arises due to mismatched label sets between the series involved in the operation. Users shared experiences and solutions, including using PromQL to handle calculations, aligning timestamps, and employing the on() operator for label matching. Some users found that resampling data helped resolve the issue. The discussion highlights the importance of understanding how Grafana handles time series data and the need for consistent label sets when performing operations. Users are encouraged to perform calculations at the PromQL level to avoid such warnings and ensure accurate results.