feat: per-merge-region streaming engine — multi-RG inputs + outputs (PR-6c.2) by g-talbot · Pull Request #6410 · quickwit-oss/quickwit

g-talbot · 2026-05-08T12:11:22Z

Summary

Restructures PR-6b.2's flat phase 0 → phase 3 into a per-merge-region loop. Unlocks multi-RG metric-aligned input support and produces multi-RG output naturally — one output row group per merge region (typically one per metric_name when rg_partition_prefix_len == 1).

Architectural insight

Sort-prefix alignment (prefix_len >= 1) guarantees that any merge region has AT MOST one row group per input. That single invariant unlocks the restructure: phase 0 no longer has to span all RGs upfront (which would force either column-chunk buffering or a second body GET); it drains one RG's sort cols per input per region as we go.

Pipeline

Pre-compute regions from RG metadata. For prefix_len >= 1, read each RG's metric_name column-chunk min stat (must equal max — verifies metric-alignment). Group RGs across inputs by prefix_key. Sort regions by prefix_key.

For prefix_len == 0 (single-RG inputs only, validated earlier), one region covers everything — behaviour matches PR-6b.2 for today's single-RG inputs.
Assign regions to output files by cumulative row count. Caller's num_outputs is preserved. Each output file gets a contiguous slice of the region list, so output files have non-overlapping key ranges.
Per-region processing: for each region in order, advance contributing inputs' decoders through their RGs (drain sort cols of that RG, then stream body cols via the existing page-bounded BodyColOutputPageAssembler). Each region becomes one output RG in the current writer; when the assignment moves to a new output file, close the previous writer and open a new one.

The streaming body-col mechanism from PR-6b.2 (arrow::compute::interleave + handle.block_on-driven decoder) is unchanged; it just runs over smaller row ranges (one region instead of one whole output).

Single-RG-input restriction lifted

PR-6b.2's check that rejected any multi-RG input is replaced with: reject only prefix_len == 0 AND multi-RG (those still need PR-5's LegacyMultiRGAdapter). Multi-RG metric-aligned inputs are now accepted natively.

Per-output schema simplification

PR-6b.2 optimised the per-output schema based on per-output sort col data (drop all-null cols, re-dict-encode low-cardinality strings). With per-region streaming we don't know each region's content until we drain it, so PR-6c.2 declares the writer's schema as the full union schema and leaves output strings as Utf8. Per-output dict re-encoding can be reintroduced later by tracking cardinality during the streaming pass.

Tests

All 9 PR-6b.2 tests still pass (single-RG input regression — behaviour preserved).
New test_multi_rg_metric_aligned_input_produces_multi_rg_output: feeds a 2-RG metric-aligned input (prefix_len = 1, RG 0 = cpu.usage, RG 1 = memory.used); the streaming engine accepts it and produces a 2-RG output (one RG per metric_name region).
Renamed test_multi_rg_input_rejected → test_legacy_multi_rg_input_rejected to reflect the new rejection scope (only prefix_len == 0 multi-RG is rejected; metric-aligned is accepted).

10/10 streaming tests pass. 442/442 crate tests pass. Clippy, doc, machete, fmt all clean.

What changed

Added:

Region struct + extract_regions_from_metadata + assign_regions_to_output_files (region pre-computation; reads parquet column chunk statistics).
OutputAccumulator — gathers per-output static metadata (row_keys, zonemap, metric_names, time_range, service names) across the regions assigned to each output file. Computed at finalize_output time.
open_output_writer_for_streaming, process_region, build_sorting_columns_from_schema, finalize_output.

Removed (PR-6b.2 multi-output-parallel helpers — no longer needed):

write_streaming_outputs, write_all_columns, write_sort_col_for_all_outputs, write_body_col_for_all_outputs, build_parent_union_schema, writer_states_index_view.
Old OutputWriterStorage struct, PerOutputStatic, build_per_output_static, derive_output_schema, open_output_writer, finalize_output_writer.

Kept:

BodyColOutputPageAssembler and its iterator (the page-bounded body col fan-out — still the streaming core).
collect_service_names_from_page, build_full_union_schema_from_arrow_schemas.

Follow-ups deferred

File-size cap with sort-key-boundary splits — when an output file's cumulative bytes-written approach a threshold, close at the next region boundary and open a new file. Adds extra splits beyond caller's N. Easy add on top of this PR's structure.
Per-output schema optimisation — track region body-col cardinality during the streaming pass; reintroduce per-output dict encoding and all-null drops.
Mid-region splits at sorted_series transitions — for finer-grained M:N control when callers want more outputs than there are metric_name regions.

Stack

Base: gtt/streaming-merge-engine-merger (PR-6b.2 #6409).

PR-7 (TBD) wires ParquetMergeExecutor to the streaming engine and deletes ParquetMergeSplitDownloader.

g-talbot · 2026-05-12T14:11:05Z

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…PR-6c.2) Restructures PR-6b.2's flat phase 0 → phase 3 into a per-merge-region loop. Unlocks multi-RG metric-aligned input support and produces multi-RG output naturally — one output row group per merge region (typically one per metric_name when `rg_partition_prefix_len == 1`). ## Architecture Sort-prefix alignment (`prefix_len >= 1`) guarantees that any merge region has AT MOST one row group per input. That single invariant unlocks the restructure: 1. Pre-compute regions from RG metadata. For `prefix_len >= 1`, read each RG's metric_name min stat (must equal max — verifies metric-alignment). Group RGs across inputs by prefix_key. Sort regions by prefix_key. For `prefix_len == 0` (single-RG inputs only, validated earlier), one region covers everything. 2. Assign regions to output files by cumulative row count. Caller's `num_outputs` preserved as the upper bound. Each output file gets a contiguous slice of the region list, so output files have non-overlapping key ranges. 3. Per-region processing: for each region, advance contributing inputs' decoders through their RGs (drain sort cols of that RG, then stream body cols via the existing page-bounded BodyColOutputPageAssembler). Each region becomes one output RG in the current writer; when the assignment moves to a new output file, close the previous writer and open a new one. The streaming body-col mechanism from PR-6b.2 (arrow::compute:: interleave + handle.block_on driven decoder) is unchanged; it just runs over smaller row ranges (one region instead of one whole output). ## Single-RG-input restriction lifted PR-6b.2's check that rejected any multi-RG input is replaced with: reject only `prefix_len == 0` AND multi-RG (those still need PR-5's LegacyMultiRGAdapter). Multi-RG metric-aligned inputs are now accepted natively. ## Per-output schema simplification PR-6b.2 optimised the per-output schema based on per-output sort col data (drop all-null cols, re-dict-encode low-cardinality strings). With per-region streaming we don't know each region's content until we drain it, so PR-6c.2 declares the writer's schema as the full union schema and leaves output strings as Utf8. Per-output dict re-encoding can be reintroduced later by tracking cardinality during the streaming pass. ## Tests - All 9 PR-6b.2 tests still pass (single-RG input regression — behaviour preserved). - New test_multi_rg_metric_aligned_input_produces_multi_rg_output: feeds a 2-RG metric-aligned input (prefix_len = 1, RG 0 = cpu.usage, RG 1 = memory.used); the streaming engine accepts it and produces a 2-RG output (one RG per metric_name region). - Renamed test_multi_rg_input_rejected → test_legacy_multi_rg_input_rejected to reflect the new rejection scope (only prefix_len == 0 multi-RG is rejected; metric-aligned is accepted). 10/10 streaming tests pass. Clippy, doc, machete, fmt all clean. ## Follow-ups deferred 1. File-size cap with sort-key-boundary splits. 2. Per-output schema optimisation (track region body-col cardinality during the streaming pass). 3. Mid-region splits at sorted_series transitions for finer-grained M:N control when callers want more outputs than regions. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

g-talbot · 2026-05-13T01:13:06Z

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Two P1 bugs flagged by Codex on PR-6c.2 (#6410): 1. **Duplicate input row groups silently dropped.** When one input contained two RGs with the same composite prefix key, `process_region` overwrote `sort_col_batches[input_idx]` while `Region::total_rows` still counted both — losing rows and misaligning the body-col / sort-col mapping. Now enforce at-most-one-RG-per-input-per-prefix as a strong invariant at three sites: the merge read path (`extract_regions_from_metadata`), the streaming merge output finalize, and the indexing writer (`ParquetWriter::write_to_bytes` / `write_to_file_with_metadata`). The new `assert_unique_rg_prefix_keys` helper is shared. 2. **Byte-array prefix encoding broke lex order across lengths.** The 4-byte length prefix made `"b"` sort before `"aa"`, violating the declared ASC order. Switched to byte-stuffed escape encoding (`0x00` → `0x00 0x01`, terminator `0x00 0x00`), which preserves single-column lex order AND retains unambiguous concatenation for composite keys (the terminator is the smallest 2-byte sequence under escaping, so shorter values still sort before longer ones with the same prefix). Tests: - `test_byte_array_prefix_preserves_lex_order_across_lengths` — `"aa" < "b"`, empty < non-empty, shared-prefix shorter < longer, null-byte escaping preserves order. - `test_streaming_merge_rejects_duplicate_prefix_rgs_in_one_input` — end-to-end bail with clear error. - `test_write_to_bytes_rejects_duplicate_rg_prefix_when_claimed_aligned` + the `write_to_file` and single-RG positive counterparts. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

g-talbot · 2026-05-13T08:13:46Z

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chatgpt-codex-connector · 2026-05-13T08:21:51Z

+        return Ok(vec![Region {
+            prefix_key: Vec::new(),
+            contributing,
+        }]);


Preserve num_outputs on the prefix_len=0 path

When the inputs have rg_partition_prefix_len == 0 (the normal single-row-group/legacy path), this branch always returns exactly one region. The outer merge loop now assigns files only at region boundaries, so num_outputs > 1 can never produce more than one output even when the merged data contains many sorted_series split points; the previous implementation used compute_output_boundaries to split the merge order within this case. Compactions of ordinary single-RG inputs requesting multiple outputs will silently create one oversized output file.

Useful? React with 👍 / 👎.

Fixed in c85bb8e — taking the broader approach we discussed offline: the prefix_len=0 path now synthesizes prefix-aligned regions during the merge rather than restoring the old compute_output_boundaries split.

Specifically: for rg_partition_prefix_len == 0 inputs, the engine drains all sort cols upfront, computes the global k-way merge order, and walks runs to find first-sort-col (e.g. metric_name) transitions. Each transition opens a synthesized region with per-input row ranges; the output writer materialises one parquet RG per region. The output is therefore prefix-aligned and declares rg_partition_prefix_len = 1 so future compactions take the fast streaming path.

Multi-output splitting falls out for free — assign_regions_to_output_files distributes the synthesized regions across files balancing row count. Regression test test_prefix_len_zero_multi_output_splits_at_prefix_transitions covers the exact num_outputs > 1 → multiple files case you flagged (6 metric_names × 50 rows + num_outputs = 3 produces 3 outputs, each declaring prefix_len = 1). Companion test test_prefix_len_zero_single_output_is_prefix_aligned_multi_rg covers num_outputs = 1 producing multi-RG output.

Plumbing: Region::contributing carries per-input start_row/num_rows so a single RG can be sliced across adjacent synthesized regions; InputDecoderState switched to per-parquet-col page cache + cursor (a HashMap keyed by col_idx) so reads of a later col that pull leftover earlier-col pages into the stream still cache them for the next synthesized region.

Followup to my previous reply: the synthesis-at-metric_name approach was wrong on two counts (caught in review): the engine was declaring prefix_len = 1 on output regardless of input, and the synthesized boundaries couldn't honor num_outputs > 1 for a giant single-metric input (no metric_name transitions to split at).

Replaced in b642371 with a sub-region splitter that breaks at sorted_series transitions whenever a region's row count would push the current output past total_rows / num_outputs, never inside a single sorted_series run. Output rg_partition_prefix_len now inherits from InputMetadata unchanged — the engine no longer declares a prefix it can't unconditionally guarantee.

New tests:

test_prefix_len_zero_multi_output_splits_at_sorted_series — original P2 case (6 metrics × 50 rows + num_outputs = 3 → 3 balanced outputs).

test_prefix_len_zero_giant_single_metric_splits_into_multiple_outputs — 1 metric × 200 rows + num_outputs = 2 → 2 outputs split at sorted_series within the one metric (the case the previous fix missed).

test_prefix_len_zero_single_output_is_single_rg — no split needed, one output, one RG, prefix KV absent.

…regions Codex P2 on PR-6c.2 (#6410): for `rg_partition_prefix_len == 0` inputs, `extract_regions_from_metadata` returned a single region spanning all inputs, and the region-to-output assigner could only split work at region boundaries. `num_outputs > 1` therefore silently produced one oversized file. The previous (non-streaming) engine sidestepped this with `compute_output_boundaries`, splitting the merge order at `sorted_series` transitions. Rather than restore the legacy split, unify the two paths: for prefix_len=0 inputs the engine now drains all sort cols upfront, computes the global k-way merge order, and walks runs to find first-sort-col (e.g. `metric_name`) transitions. Each transition opens a new synthesized region carrying per-input row ranges; the output writer materialises one parquet row group per region. The output is therefore prefix-aligned (each RG carries a single first- sort-col value) and the writer advertises `rg_partition_prefix_len = 1` so future compactions take the fast streaming path. Multi-output splitting falls out for free: the existing `assign_regions_to_output_files` distributes synthesized regions across files balancing row count. Mechanical pieces: - `Region::contributing` becomes `Vec<RegionContribution>` with `start_row` per input, so a single RG can be sliced across multiple adjacent regions. - `InputDecoderState` switches from one-active-col page cache + cursor to per-parquet-col HashMaps. `advance_decoder_to_row` now stores pages under their actual `col_idx`, so reads of a later col that pull leftover earlier-col pages into the stream keep them cached for the next synthesized region to consume. - `set_body_col_cursor` replaces `reset_body_col_state`: it positions the cursor and drops only pages strictly below it, preserving rows that still belong to future regions. - `process_region` accepts an optional `prefetched_sort_batches` argument. When supplied (the synthesized path) it slices the pre- drained sort batches by each contribution's row range; when `None` (the existing prefix_len>0 path) it drains a fresh whole-RG batch from the decoder, same as before. Tests: - `test_prefix_len_zero_multi_output_splits_at_prefix_transitions` — 6 metric_names × 50 rows + `num_outputs = 3` produces 3 output files; each declares `rg_partition_prefix_len = 1`. - `test_prefix_len_zero_single_output_is_prefix_aligned_multi_rg` — 3 metric_names + `num_outputs = 1` produces one file with 3 RGs, declaring `rg_partition_prefix_len = 1`. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

…sizing prefix Per review feedback: the prior commit incorrectly conflated "fix the prefix_len=0 multi-output regression" with "make every legacy output prefix-aligned at the engine layer." Two issues with that approach: 1. The engine was declaring `rg_partition_prefix_len = 1` on outputs regardless of what the inputs claimed. That's a property the engine guessed and forced; it should come from the inputs (or from a future legacy-converter layer that translates legacy inputs into prefix-aligned form before the engine sees them). 2. Synthesizing regions at first-sort-col transitions doesn't honor `num_outputs` when there are no such transitions — a giant single metric with `prefix_len = 0` would still collapse into one output even with `num_outputs = 3`. New strategy: keep the per-col page cache and `RegionContribution` row-range plumbing — both are still needed — but replace the metric_name-transition synthesis with a sub-region splitter that breaks at `sorted_series` transitions whenever a region's row count would push the current output past `target_per_output = total_rows / num_outputs`. Splitting happens at run boundaries only — never inside a `sorted_series` run — so a single huge run lands in one output regardless of size. The output's `rg_partition_prefix_len` is inherited from `InputMetadata` unchanged. Main-loop shape: for each top-level region the engine first asks "would this region fit in the current output's remaining budget?" If yes, `process_region` drains internally as before (per-region memory bound preserved). If not, pre-drain the region's sort cols, compute its merge order, call `split_region_at_sorted_series` to get sub-regions, then process each sub-region with the prefetched batches. Between top-level regions we now `reset_all_body_col_state` on every input — different RGs have overlapping row-index spaces and their cached pages would collide. Sub-regions of one top-level region share an RG and keep the cache; this is what lets an earlier col's stream-tail get cached during a later col's read and remain available for the next sub-region. Tests rewritten: - `test_prefix_len_zero_multi_output_splits_at_sorted_series` — 6 metrics × 50 rows, `num_outputs = 3` → 3 outputs balanced near 100 rows each. Asserts the output's `rg_partition_prefix_len` KV is absent (inherits input's 0). - `test_prefix_len_zero_giant_single_metric_splits_into_multiple_outputs` — covers the giant-metric case: 1 metric × 200 rows, `num_outputs = 2` → 2 outputs, splitting at `sorted_series` transitions inside the single metric. - `test_prefix_len_zero_single_output_is_single_rg` — `num_outputs = 1` produces a single output with a single RG and no prefix KV. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

The legacy adapter previously consolidated multi-RG legacy inputs into a single oversized row group and left `rg_partition_prefix_len` at the original's (typically `0`). The streaming merge engine then sent these single-RG/prefix=0 inputs through the new sub-region splitting path — correct, but it forfeits the prefix-aware fast path for outputs derived from legacy inputs and gives up the row-group pruning that prefix alignment enables. After consolidating, the adapter now slices the resulting record batch at first-sort-col transitions (typically `metric_name`) and emits one parquet row group per slice, stamping the re-encoded file with `qh.rg_partition_prefix_len = 1`. The merge engine then reads it through the prefix-aware fast path: one region per metric_name, the existing duplicate-prefix invariant on read validates uniqueness. Fallback: if the original file has no `qh.sort_fields` KV, the sort-fields string fails to parse, the first column can't be resolved in the arrow schema, or the consolidated batch is empty, the adapter reverts to a single-RG re-encode without claiming any prefix alignment. That input still works — the engine's prefix_len=0 sub-region splitting path picks it up. This keeps the adapter robust for files written by very early versions of the indexer that may pre-date the standard KV layout. Implementation: `reencode_prefix_aligned` replaces `reencode_as_single_row_group` and either dispatches to the new multi-RG writer or to the legacy single-RG writer based on whether the first sort col is resolvable. `RowConverter` handles the prefix-value equality check uniformly across dictionary, utf8, and primitive types. The KV injection helper replaces (rather than appends) any existing `qh.rg_partition_prefix_len` so re-runs and files mistakenly carrying a stale value still land at the freshly synthesized prefix. Tests: - `test_legacy_input_with_sort_fields_produces_prefix_aligned_multi_rg` — 3 metrics × 40 rows, multi-RG input → 3 prefix-aligned output RGs and `qh.rg_partition_prefix_len = 1` KV. - `test_legacy_input_single_metric_yields_one_rg_with_prefix_kv` — one metric → one RG, prefix KV still stamped (vacuously aligned). - `test_legacy_input_without_sort_fields_falls_back_to_single_rg` — fallback path preserved when sort-fields KV is missing. - All existing tests pass unchanged (they use empty KVs or unparseable sort-fields strings, both of which exercise the fallback path). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

…e-prefix support `LegacyInputAdapter::try_open` now takes `target_prefix_len: u32` chosen by the caller, matching the merge plan's consensus prefix length. The adapter slices the consolidated batch at every transition of the first N sort columns (composite key, via `RowConverter` over all N fields) and emits one output row group per slice, stamping the output with `qh.rg_partition_prefix_len = target_prefix_len`. With `target_prefix_len = 0` the adapter takes the original single-RG passthrough path with no prefix-alignment claim. A sort column that is named in `qh.sort_fields` but missing from the file's arrow schema is treated as implicitly null at every row per SS-3. A constantly-null column trivially satisfies alignment on that column (null == null) and contributes no transitions, so the split boundaries are driven by the columns that are present. This matches the merge engine's compaction-time treatment of missing columns and keeps a legacy file with an evolved schema usable as a prefix-aligned input. `PrefixUnresolvable` now fires only on cases where the file doesn't advertise enough sort *names* to honor the request: - `qh.sort_fields` absent or unparseable - `qh.sort_fields` declares fewer sort columns than `target_prefix_len` A column missing from the arrow schema no longer counts as unresolvable; the adapter materialises a `NullArray` of the batch's length in that slot and proceeds. Tests: - `test_target_prefix_len_zero_passes_through_as_single_rg` — explicit N=0 fallback, no prefix KV stamped. - `test_target_prefix_len_two_splits_by_metric_and_service` — composite prefix (`metric_name`, `service`) → 4 RGs, KV declares prefix_len=2. - `test_target_prefix_len_one_without_sort_fields_returns_unresolvable` — no `qh.sort_fields` KV → `PrefixUnresolvable`. - `test_target_prefix_len_exceeds_declared_sort_cols_returns_unresolvable` — sort schema declares 2 cols, caller asks 3 → `PrefixUnresolvable`. - `test_missing_prefix_col_treated_as_null_satisfies_alignment` — sort schema declares `metric_name|env|-timestamp_secs` but `env` is absent from the arrow schema → no error, only metric_name transitions split RGs, KV still stamps prefix_len=2. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

…KV stamp The streaming merge engine produces sort-prefix-aligned multi-RG output and stamps `qh.rg_partition_prefix_len = input_meta.rg_partition_prefix_len` in the file's KV (verified by `assert_unique_rg_prefix_keys` before close). `merge_parquet_split_metadata` then ran after and unconditionally demoted to 0 whenever `output.num_row_groups > 1` — breaking CS-1 (metastore must mirror on-disk KV) for every multi-RG streaming-engine output. Aligned splits got tagged 0 in the metastore on every merge and leaked out of the prefix-aligned compaction bucket on the next pass. Carry the value the writer actually stamped via a new `MergeOutputFile.output_rg_partition_prefix_len` field, then propagate it as-is in metadata aggregation. Both engines populate the field: - Legacy `merge/writer.rs` reports its demoted value (row-count-driven RG boundaries can't honor prefix alignment, so it stamps 0 on multi-RG). - Streaming `merge/streaming/output.rs` reports the inputs' prefix unchanged (it splits at prefix transitions and the writer verifies). CS-1 holds by construction — same source of truth, no re-derivation. Tests: - `test_output_prefix_len_demoted_when_multi_rg` → renamed to `test_output_prefix_len_carries_writers_value_when_demoted`; now asserts that the metastore mirrors the writer's reported value. - New `test_output_prefix_len_preserved_on_multi_rg_streaming_engine` asserts that a multi-RG streaming output (writer reports prefix_len=2) keeps the prefix in the metastore — the regression case for F1. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

…onger test verifiers Three adversarial-review findings on the prefix/RG machinery, bundled because they touch the same producer/consumer contract: **F8: Legacy adapter rejects SS-1-violating input upfront.** The adapter walked rows in physical order and emitted one RG per prefix-value run. An unsorted legacy input (rows `[A,A,B,B,A,A]`) produced a 3-RG file where two RGs shared prefix `A`, violating PA-3. The streaming merge engine would later reject it mid-merge — but only after a quietly-bad file had been built. Now `compute_prefix_value_slices` tracks each slice's composite prefix-value bytes and bails with `LegacyAdapterError::InputNotSorted` on duplicates, surfacing the SS-1 violation before any file lands on disk. **F12: Consumer-side SS-3 (cross-layer divergence, discovered while wiring F2's chunk-level verifier into the SS-3 test).** The adapter implements SS-3 correctly (missing-from-schema → synthesized NullArray during slice computation, file stamps `prefix_len = N`). The streaming engine's reader did not: `find_prefix_parquet_col_indices` hard-required every named prefix column to be physically present, so a file the adapter produced from an SS-3 input was unreadable by the merge engine. Now `find_prefix_parquet_col_indices` returns `Vec<Option<PrefixColumn>>` and `extract_rg_composite_prefix_key` emits a constant null marker (`encode_byte_array_prefix(&[])`) for None slots. The column contributes no cross-RG ordering signal (constant everywhere) so region boundaries are driven entirely by the present columns. Both halves of SS-3 now agree end-to-end. Known limitation: cross-file SS-3 — where some inputs have a sort column and others don't — uses [0x00, 0x00] for the null contribution, which sorts BEFORE non-null per the encoded-empty-string convention. That weakly violates SS-2 (nulls sort last). Single-file SS-3 is correct because every RG in such a file contributes the same constant. If cross-file SS-3 becomes a production scenario, the encoding needs a leading-0xff sentinel instead. Not exercised today. **F2/F9/F11: Wire `assert_unique_rg_prefix_keys` into prefix-claiming tests.** Tests asserting `num_row_groups == N` + KV stamped to N would have passed even with an off-by-one in slice-boundary detection or column-content scrambling. The verifier reads chunk-level statistics directly: PA-1 (intra-RG `min == max`) + PA-3 (inter-RG uniqueness) on the composite key. Wired into six tests: - streaming engine: `test_streaming_merge_with_prefix_len_two`, `test_multi_rg_metric_aligned_input_produces_multi_rg_output`, `test_streaming_merge_with_desc_prefix_col` - legacy adapter: `test_target_prefix_len_two_splits_by_metric_and_service`, `test_legacy_input_with_sort_fields_produces_prefix_aligned_multi_rg`, `test_missing_prefix_col_treated_as_null_satisfies_alignment` (now passes thanks to F12). Also: `assert_unique_rg_prefix_keys` no longer short-circuits on single-RG files — they still go through PA-1 because an unsorted single-RG file CAN have `min != max` on a prefix column. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

g-talbot · 2026-05-13T15:24:32Z

Sliced into three stacked PRs for easier review — same final tree, just reorganized commits:

feat(streaming-merge): per-region engine + multi-output sorted_series splitting #6424 — per-region streaming engine + multi-output sorted_series splitting (slice 1, ~2700 lines)
feat(legacy-adapter): prefix-aware output with caller-supplied target_prefix_len #6425 — legacy adapter prefix-aware output (slice 2, ~900 lines)
fix(merge): adversarial-review hardening — CS-1, adapter self-verify, chunk-level test verifier #6426 — adversarial-review hardening (slice 3, ~1000 lines, addresses F1/F2/F8/F9/F11/F12)

PR #6423 (legacy promotion + body-col schema evolution) is being rebased onto #6426.

The branch backing this PR (gtt/streaming-merge-engine-multi-rg) is preserved for reference; no force-push happened here. The three new branches contain an identical tree at the top via cherry-pick (forward synth + correction pair squashed into one commit).

… splitting (#6424) * feat: per-merge-region streaming engine — multi-RG inputs + outputs (PR-6c.2) Restructures PR-6b.2's flat phase 0 → phase 3 into a per-merge-region loop. Unlocks multi-RG metric-aligned input support and produces multi-RG output naturally — one output row group per merge region (typically one per metric_name when `rg_partition_prefix_len == 1`). Sort-prefix alignment (`prefix_len >= 1`) guarantees that any merge region has AT MOST one row group per input. That single invariant unlocks the restructure: 1. Pre-compute regions from RG metadata. For `prefix_len >= 1`, read each RG's metric_name min stat (must equal max — verifies metric-alignment). Group RGs across inputs by prefix_key. Sort regions by prefix_key. For `prefix_len == 0` (single-RG inputs only, validated earlier), one region covers everything. 2. Assign regions to output files by cumulative row count. Caller's `num_outputs` preserved as the upper bound. Each output file gets a contiguous slice of the region list, so output files have non-overlapping key ranges. 3. Per-region processing: for each region, advance contributing inputs' decoders through their RGs (drain sort cols of that RG, then stream body cols via the existing page-bounded BodyColOutputPageAssembler). Each region becomes one output RG in the current writer; when the assignment moves to a new output file, close the previous writer and open a new one. The streaming body-col mechanism from PR-6b.2 (arrow::compute:: interleave + handle.block_on driven decoder) is unchanged; it just runs over smaller row ranges (one region instead of one whole output). PR-6b.2's check that rejected any multi-RG input is replaced with: reject only `prefix_len == 0` AND multi-RG (those still need PR-5's LegacyMultiRGAdapter). Multi-RG metric-aligned inputs are now accepted natively. PR-6b.2 optimised the per-output schema based on per-output sort col data (drop all-null cols, re-dict-encode low-cardinality strings). With per-region streaming we don't know each region's content until we drain it, so PR-6c.2 declares the writer's schema as the full union schema and leaves output strings as Utf8. Per-output dict re-encoding can be reintroduced later by tracking cardinality during the streaming pass. - All 9 PR-6b.2 tests still pass (single-RG input regression — behaviour preserved). - New test_multi_rg_metric_aligned_input_produces_multi_rg_output: feeds a 2-RG metric-aligned input (prefix_len = 1, RG 0 = cpu.usage, RG 1 = memory.used); the streaming engine accepts it and produces a 2-RG output (one RG per metric_name region). - Renamed test_multi_rg_input_rejected → test_legacy_multi_rg_input_rejected to reflect the new rejection scope (only prefix_len == 0 multi-RG is rejected; metric-aligned is accepted). 10/10 streaming tests pass. Clippy, doc, machete, fmt all clean. 1. File-size cap with sort-key-boundary splits. 2. Per-output schema optimisation (track region body-col cardinality during the streaming pass). 3. Mid-region splits at sorted_series transitions for finer-grained M:N control when callers want more outputs than regions. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com> * fix(streaming): reject duplicate-prefix RGs + use escape encoding Two P1 bugs flagged by Codex on PR-6c.2 (#6410): 1. **Duplicate input row groups silently dropped.** When one input contained two RGs with the same composite prefix key, `process_region` overwrote `sort_col_batches[input_idx]` while `Region::total_rows` still counted both — losing rows and misaligning the body-col / sort-col mapping. Now enforce at-most-one-RG-per-input-per-prefix as a strong invariant at three sites: the merge read path (`extract_regions_from_metadata`), the streaming merge output finalize, and the indexing writer (`ParquetWriter::write_to_bytes` / `write_to_file_with_metadata`). The new `assert_unique_rg_prefix_keys` helper is shared. 2. **Byte-array prefix encoding broke lex order across lengths.** The 4-byte length prefix made `"b"` sort before `"aa"`, violating the declared ASC order. Switched to byte-stuffed escape encoding (`0x00` → `0x00 0x01`, terminator `0x00 0x00`), which preserves single-column lex order AND retains unambiguous concatenation for composite keys (the terminator is the smallest 2-byte sequence under escaping, so shorter values still sort before longer ones with the same prefix). Tests: - `test_byte_array_prefix_preserves_lex_order_across_lengths` — `"aa" < "b"`, empty < non-empty, shared-prefix shorter < longer, null-byte escaping preserves order. - `test_streaming_merge_rejects_duplicate_prefix_rgs_in_one_input` — end-to-end bail with clear error. - `test_write_to_bytes_rejects_duplicate_rg_prefix_when_claimed_aligned` + the `write_to_file` and single-RG positive counterparts. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com> * feat(streaming): split regions at sorted_series for prefix_len=0 multi-output When inputs declare rg_partition_prefix_len = 0 (legacy single-RG) and the caller asks for num_outputs > 1, the engine subdivides the single region at sorted_series transitions in the merge order so it can honor the output count. A single sorted_series run is never broken; if one run exceeds the remaining budget the whole run lands in one output anyway. The output inherits the input's rg_partition_prefix_len (=0) — the engine does not synthesize a prefix it can't unconditionally guarantee. Also handles the giant-single-metric case (prefix_len=0, one metric_name, num_outputs > 1): sorted_series transitions still split the merge order even though there are no metric_name transitions to drive a prefix synthesis. Implementation: - New `split_region_at_sorted_series` in region_grouping: walks the merge order and splits at sorted_series transitions when accumulated rows reach the target budget. - Main engine loop: when num_outputs > current_output_idx + 1 AND region's rows exceed the remaining budget, drain sort cols for the region, compute merge order, call split_region_at_sorted_series, process sub-regions. - Per-col page cache + cursor keyed by col_idx so the body-col path can read pages once and re-use them across sub-regions within the same top-level region. Resets between top-level regions (different RGs). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com> * docs(streaming): correct 'crash' → 'bail' in MS-2 doc comments The MS-2 validation path returns `Err` via `bail!()` (anyhow), not a panic / abort. Five doc-comment / inline-comment sites described the failure as "the engine would crash mid-merge" — overstated. Callers get a `Result::Err` propagated up the spawn_blocking task and the `streaming_merge_sorted_parquet_files` return. Sites updated: - `region_grouping.rs` module doc. - `validate_region_order_matches_physical_rg_order` doc. - streaming.rs MS-2 validation call-site comment. - Test docstrings for `test_streaming_merge_with_desc_prefix_col` and `test_ms2_region_order_disagrees_with_physical_rg_order_rejected`. No behaviour change. 477 lib tests pass; clippy + nightly fmt clean. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com> * docs(streaming): fix wrong adapter type name + explain rejection intent Two sites referenced a non-existent `LegacyMultiRGAdapter` — the actual type, introduced in PR-5 (#6408), is `LegacyInputAdapter` in `storage::legacy_adapter`. Fixed both references. Also expanded the rejection-block comment to make the *intent* of the guard explicit: it catches caller bugs (wiring a raw legacy multi-RG `StreamingParquetReader` straight into the streaming merge), not a degraded-input fallback. Production code routes legacy splits through `merge::execute_merge_operation` which wraps them in `LegacyInputAdapter` first. No behaviour change. Targeted test passes. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com> * fix(body_assembler): tighten output-iter termination + assert invariant adamtobey nit on PR #6424: `rows_emitted >= expected_rows` accepts `emitted > expected` as a normal termination condition, which would actually be a real accounting bug. The math rules `>` out by construction — `page_size = remaining.min(OUTPUT_PAGE_ROWS)` where `remaining = expected_rows - rows_emitted`, so each `rows_emitted += page_size` keeps `rows_emitted ≤ expected_rows`. Two changes: - Termination becomes `rows_emitted == expected_rows` so we don't silently accept an overshoot. - `debug_assert!(rows_emitted <= expected_rows, …)` at the top of `next()` documents the invariant and surfaces a regression loudly (panic in debug + tests) instead of silently terminating one iteration too late. No behaviour change in the happy path; bugs that would have produced `>` now fail tests instead of producing wrong output. 477 lib tests pass; clippy + nightly fmt clean. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com> * fix(streaming): recompute split budget across the output-rollover boundary Codex P1 finding on PR #6424: when a top-level region exactly fills the current output (so `remaining_in_current == 0`) and the next prefix-aligned region needs splitting, the split's first-sub-region budget was the stale zero remainder of the about-to-be-finalized output. `split_region_at_sorted_series` therefore cut after the first sorted_series run, producing a tiny leftover plus a large continuation that both inherited the parent region's prefix key. The sub-region loop then rolled over to a fresh output and wrote both pieces there, tripping the PA-3 duplicate-prefix-RG check in `finalize_output`. Fix: detect the rollover at decision time and compute `effective_first_target` / `effective_outputs_remaining` against the *next* output's empty budget. With the fix, the example above just chooses `needs_split = false` (region fits the fresh output's full target), processes the region whole, and rolls over cleanly. Regression test `test_region_exactly_fills_output_does_not_split_next_aligned_region` exercises the exact scenario Codex described: three 50-row RGs with distinct (metric, service) prefixes, `num_outputs = 3`, target = 50. Pre-fix, the merge bailed with PA-3 on output 1; post-fix, three clean outputs each with one unique prefix key. Verified by reading each output's parquet metadata back through `assert_unique_rg_prefix_keys`. 478 lib tests pass (477 prior + 1 new); clippy + nightly fmt clean. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com> * fix(streaming): reject null-mixed + all-null prefix RGs Codex P1 on PR #6424: `extract_aligned_prefix_value` decided prefix alignment purely from `min` / `max` statistics. Parquet records those over non-null cells only, with `null_count` reported separately, so two real failure modes slipped through: 1. **Mixed null + non-null.** A row group with `N` nulls plus a single non-null cell `"x"` reports `min == max == "x"` and the `min == max` check silently accepted it — but two distinct prefix keys (null and `"x"`) lived in that RG, breaking the at-most-one-prefix-value-per-RG invariant (PA-1). 2. **All-null RG.** Parquet records no `min` / `max` for an all- null chunk, so the legacy check bailed with the misleading "no min in stats" error. Logically the RG carries one prefix value (null) and is aligned — but supporting it cleanly requires a null marker in the composite-key encoding that agrees with SS-2's "nulls last" rule. `encode_byte_array_prefix(&[])` puts nulls *first*; coordinating that with SS-2 is a follow-up. Fix: read `null_count_opt()` from stats and `num_values()` from the column-chunk metadata. Bail explicitly in both cases — mixed with a PA-1 message naming the (nulls, non-null) split, all-null with a clear "not yet supported" pointer. Two regression tests in `streaming.rs::tests`: - `test_mixed_null_and_value_prefix_rg_rejected`: 1 RG, 3 cells `"cpu.usage"` + 1 null. Asserts PA-1 bail. - `test_all_null_prefix_rg_rejected`: 1 RG, 3 nulls. Asserts the "all-null … not yet supported" bail. 480 lib tests pass (+2 new); workspace clippy + nightly fmt clean. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com> * refactor(streaming): share storekey prefix encoding with sorted_series The per-RG composite prefix key now uses the same storekey-based encoding as `sorted_series` — same `(ordinal, value)` layout, same direction-inversion, same null-skip pattern — so a per-RG prefix key is a literal byte prefix of every `sorted_series` value emitted by rows in that RG. Why: the prior byte-stuffed escape encoding had no in-line way to represent an all-null prefix RG (an empty marker would lex-sort before any present-value key, conflicting with SS-2 nulls-last). With the shared encoding, an all-null column is skipped entirely and the next column's higher ordinal byte appears in its place, giving nulls-last ordering for free — the same trick already proven in `sorted_series::encode_row_key`. Per-column logic now goes through one helper: `crate::sorted_series::append_prefix_col_to_key(buf, ord, val, desc)` shared between `sorted_series` (per-row keys) and `merge::streaming::region_grouping` (per-RG keys). It writes `storekey(ord) || storekey(val)` and inverts only the value bytes for DESC columns. `sorted_series::encode_row_key` was refactored to call the helper; the open-coded inline encoding is gone. Trailing **prefix-length sentinel**: each per-RG key ends with a `u8(prefix_len)` ordinal byte. This handles the prefix_len=1 edge case where an all-null RG's empty body would otherwise lex-sort *before* any non-null RG — with the sentinel, the all-null key becomes `[prefix_len]` and non-null keys still start with `ord(0)` (< prefix_len), so non-null sorts first. The sentinel is also what `sorted_series` writes immediately after the prefix cols, so the literal-prefix property is preserved. Null handling in `extract_rg_composite_prefix_key`: - **All-null RG**: column skipped, RG groups into its own region (after non-null regions). - **Mixed null + non-null**: rejected as a PA-1 violation (rows in the same RG would encode to two distinct prefix keys; producer is supposed to start a new RG at the null/non-null transition). - **Otherwise**: standard `min == max` check, then the type-dispatched storekey encoding via the helper. Removed: - `extract_aligned_prefix_value` (replaced by `encode_prefix_col_value` which calls the helper). - `encode_byte_array_prefix` (byte-stuffed escape, no longer used). - `invert_for_descending` (the helper handles inversion per-column). - `test_invert_for_descending_reverses_lex_order` and `test_byte_array_prefix_preserves_lex_order_across_lengths` (byte-level tests of the removed encoding; semantic properties remain enforced by `storekey`'s own tests plus the higher-level prefix tests). Replaced `test_all_null_prefix_rg_rejected` with `test_all_null_prefix_rg_groups_into_separate_region_sorted_last`: builds two inputs (one with `metric_name = "cpu.usage"`, one with `metric_name = NULL`) and verifies the merged output has two RGs with the all-null region in RG 1 (sorted after the non-null region) — pinning the nulls-last ordering that the sentinel encoding produces. Updated `test_extract_rg_composite_prefix_key_two_byte_array_cols` for the new byte layout (`storekey(ord) || storekey(val)` per col plus the trailing sentinel byte). `PrefixColumn` gains an `ordinal: u8` field, populated from each column's position in `qh.sort_fields` so it matches the ordinal `sorted_series` would assign. 478 lib tests pass; workspace clippy + nightly fmt clean. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com> * style(streaming): re-fmt to latest nightly rustfmt CI's nightly rustfmt (1.9.0-nightly 2026-05-17) wrapped a handful of comment / bail!-message / where-clause / vec! literal lines slightly differently than my local nightly at commit time (1.9.0-nightly 2026-05-11). Re-formatting all three affected files catches the drift in this commit so CI Lints stops complaining; local nightly is now updated to match CI. No behaviour change. 478 lib tests still pass on the slice. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com> * fix(merge): preserve metastore rg_partition_prefix_len from writer's KV stamp The streaming merge engine produces sort-prefix-aligned multi-RG output and stamps `qh.rg_partition_prefix_len = input_meta.rg_partition_prefix_len` in the file's KV (verified by `assert_unique_rg_prefix_keys` before close). `merge_parquet_split_metadata` then ran after and unconditionally demoted to 0 whenever `output.num_row_groups > 1` — breaking CS-1 (metastore must mirror on-disk KV) for every multi-RG streaming-engine output. Aligned splits got tagged 0 in the metastore on every merge and leaked out of the prefix-aligned compaction bucket on the next pass. Carry the value the writer actually stamped via a new `MergeOutputFile.output_rg_partition_prefix_len` field, then propagate it as-is in metadata aggregation. Both engines populate the field: - Legacy `merge/writer.rs` reports its demoted value (row-count-driven RG boundaries can't honor prefix alignment, so it stamps 0 on multi-RG). - Streaming `merge/streaming/output.rs` reports the inputs' prefix unchanged (it splits at prefix transitions and the writer verifies). CS-1 holds by construction — same source of truth, no re-derivation. Tests: - `test_output_prefix_len_demoted_when_multi_rg` → renamed to `test_output_prefix_len_carries_writers_value_when_demoted`; now asserts that the metastore mirrors the writer's reported value. - New `test_output_prefix_len_preserved_on_multi_rg_streaming_engine` asserts that a multi-RG streaming output (writer reports prefix_len=2) keeps the prefix in the metastore — the regression case for F1. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com> --------- Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

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feat: streaming column-major merge engine with page-bounded body cols (PR-6b.2) #6409

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feat: per-merge-region streaming engine — multi-RG inputs + outputs (PR-6c.2)#6410

feat: per-merge-region streaming engine — multi-RG inputs + outputs (PR-6c.2)#6410
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