Add the JSONBench benchmark suite

[joseph-isaacs]

Summary

Adds ClickHouse's JSONBench to vortex-bench as jsonbench. It runs five analytical queries over Bluesky events stored as semi-structured JSON. It is the first suite that exercises Variant columns, and it gives the upcoming Variant work a baseline to measure against.

This PR only adds the suite. It is not in the CI benchmark matrix. Two kinds of target need engine support that will come in follow-up PRs:

• DataFusion over parquet-variant and vortex: DataFusion has no variant_get function registered yet.
• DuckDB over vortex: read_vortex does not expose Vortex Variant columns yet.

The JSON-string Parquet baseline only uses functions that already exist: datafusion-functions-json on DataFusion and json_extract_string on DuckDB.

Changes

• vortex-bench/src/jsonbench
  • Downloads the raw event files from ClickHouse's public bucket, one file per million events. --opt scale-factor=N picks how many files.
  • Infers which JSON paths to shred from the data and saves them to shredding.json.
  • Writes three formats from the same events:
    • parquet: the event as a JSON string.
    • parquet-variant: the event as a shredded Parquet Variant column. This is the new Format::ParquetVariant.
    • vortex: the event as a shredded Vortex Variant column, converted from the Parquet Variant files.
• Queries (vortex-bench/sql/jsonbench.sql) read JSON paths through {str:a.b} and {i64:a.b} placeholders. The new Benchmark::query_for lets a suite rewrite its SQL for each engine and format; by default it returns the query unchanged.
• Data generation and duckdb-bench now run a suite's prepare_format before the generic Parquet-to-Vortex conversion, so JSONBench writes its own Vortex files. The Parquet-to-Vortex conversion now hands Variant chunks to the writer unchanged, because Variant has no array builder.
• datafusion-bench registers datafusion-functions-json when running JSONBench. It is a new workspace dependency.
• VX_BENCH_PRINT_RESULTS=1 prints each query's result, for comparing formats and engines.
• bench-orchestrator knows the jsonbench suite and the parquet-variant format, but neither is added to a CI preset.
• Docs: vortex-bench/sql/jsonbench.md.

[codspeed]

Merging this PR will not alter performance

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

✅ 2111 untouched benchmarks
⏩ 518 skipped benchmarks¹

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_{Comparing ji/jsonbench-suite (1d6ff33) with develop (f234bc6)}

Footnotes

1. 518 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.26%. Comparing base (9eb20ba) to head (b20730a).
⚠️ Report is 1 commits behind head on develop.

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