feat: compute per-output split metadata in merge engine#6359
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g-talbot wants to merge 2 commits intogtt/parquet-merge-policy-configfrom
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feat: compute per-output split metadata in merge engine#6359g-talbot wants to merge 2 commits intogtt/parquet-merge-policy-configfrom
g-talbot wants to merge 2 commits intogtt/parquet-merge-policy-configfrom
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The merge engine now extracts metric_names, time_range, and low_cardinality_tags from each output file's actual rows during the merge write pass. Previously, MergeOutputFile only contained physical metadata (num_rows, size_bytes, row_keys, zonemaps). The downstream metadata_aggregation function inferred logical metadata by unioning all input splits — which is incorrect when num_outputs > 1, since each output contains only a subset of the globally sorted rows. Now each MergeOutputFile carries: - metric_names: distinct metrics in this output's rows - time_range: min/max timestamp_secs from this output's rows - low_cardinality_tags: service names from this output's rows Reuses existing extract_metric_names, extract_service_names, and extract_time_range from split_writer (made pub(crate)). Includes test that verifies per-output metadata is computed from actual rows when merging 2 inputs into 2 outputs with different metric names. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Summary
Stacked on #6351 (Phase 2). Should be merged before #6352 (Phase 3a).
The merge engine now extracts
metric_names,time_range, andlow_cardinality_tags(service) from each output file's actual rows during the merge write pass.Problem:
MergeOutputFilepreviously only had physical metadata (num_rows, size_bytes, row_keys, zonemaps). The downstreammetadata_aggregationfunction inferred logical metadata by unioning all input splits. This is incorrect whennum_outputs > 1— each output contains a different subset of the globally sorted rows and should have metadata reflecting only its own data.Fix: Each
MergeOutputFilenow carries per-output logical metadata extracted from thesorted_batchbefore writing. Reusesextract_metric_names,extract_service_names,extract_time_rangefromsplit_writer(madepub(crate)).Test plan
test_merge_per_output_metadata_from_actual_rows— verifies 2-output merge has correct per-output metric_names and time_rangetest_merge_multiple_outputswith per-output metadata assertionscargo clippyclean🤖 Generated with Claude Code