Add the flat nz map producer and its DELTA_BINARY consumer by vyasr · Pull Request #24501 · NVIDIA/cudf

vyasr · 2026-10-08T03:56:55Z

Description

Introduces a producer/consumer kernel pair for the nz map, behind LIBCUDF_PARQUET_NZ_MAP. The nz map is nz_idx[rank] = input position of the rank-th valid value, plus its length nz_count.

Producer — precompute_flat_nz_map walks a page's already-decoded definition levels once, writing the leaf column's null mask and the nz map.
Consumer — decode_delta_binary_kernel_with_nz_map reads that map and places values without decoding levels, so it runs two warps rather than the level-decoding kernel's three: a delta producer and a value writer, the writer trailing by one batch so the two overlap in a single phase.

Both cover DELTA_BINARY_PACKED pages of flat columns — max_level[REPETITION] == 0 && max_nesting_depth <= 1, so not inside a list or struct and values line up one-to-one with output rows. Both nullable and and non-nullable pages both qualify. A non-nullable page's map is the identity, so map allocation is skipped and the consumer synthesizes it on the fly. Other encodings and shapes follow in later PRs.

decode_delta_binary_kernel is unmodified. Routing goes through a page mask that the host seeds and the producer clears per page, so the two kernels partition the pages without a second kernel re-deriving the decision. That mask is transitional: an in-code TODO records that once every delta kernel has a consumer and the default flips, each can test has_nz_map() directly and the buffer, its per-subpass allocation and the producer's store all go away.

Renamed from "prepass" to "nz map"

"Prepass" collides with pass and subpass, which are existing reader concepts (pass_intermediate_data, subpass_intermediate_data), and page_delta_decode.cu already contains an unrelated string-size prepass. The feature is renamed for what it produces, reusing vocabulary already in the tree. PagePrepassState → page_nz_map, level_prepass_family → nz_map_kind, is_prepass_family() → has_nz_map(), LIBCUDF_PARQUET_LEVEL_PREPASS → LIBCUDF_PARQUET_NZ_MAP.

Performance

parquet_read_delta_binary_nullable_page_sizes and parquet_read_delta_binary, H100 with clocks locked, off → on:

case	change
50% nulls	−25%
required (non-nullable) columns	−4.8%
1% nulls	break-even

The gain scales with how much level-decoding work the map removes. At 50% nulls the bit-packed level walk it replaces is expensive; on required columns no map is allocated, so the gain is the narrower block alone. At 1% nulls the levels are a cheap RLE run and the map's own traffic — 4 bytes per value written, 4 per valid value read, against levels at 1–2 bytes per value — costs about what it saves. Narrowing the map's index width for pages under 64k values is the fix, tracked for before the default flips along with counting this scratch in the chunked-read budget.

Contributes to #23965.

Checklist

I am familiar with the Contributing Guidelines.
New or existing tests cover these changes.
The documentation is up to date with these changes.

copy-pr-bot · 2026-10-08T03:56:59Z

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…umer Second of the nz map series. This one makes the feature do something, but only under `LIBCUDF_PARQUET_NZ_MAP=1`; unset, nothing below runs and no scratch is allocated. The nz map is `nz_idx[rank] = input position of the rank-th valid value`, plus its length `nz_count`. Naming it for the fields it holds keeps it clear of the reader's own `pass` / `subpass`, which an earlier "prepass" spelling collided with -- this file already has an unrelated string-size prepass. Producer -- `precompute_nz_map` (decode_preprocess.cu) walks a claimed page's already-decoded definition levels once, writing the leaf column's null mask and the map, then records `nz_count`. A required page needs no map -- its map is the identity -- and a null `nz_idx` is what tells the consumer to synthesize it. The block-wide rank is taken from the ballot the loop already computes, rather than from a `cub::BlockScan` over the same predicate, and the map pointer is hoisted out of the loop: `PageInfo*` is not restrict-qualified, so each iteration otherwise re-chased two dependent global loads to set up one 4-byte store. Shared memory drops from 2708 to 2048 bytes per block and the kernel no longer spills. At 40 registers and 128 threads it runs 12 blocks per SM, or 48 warps; the block scan was not what bounded that. Consumer -- `decode_delta_binary_kernel_with_nz_map` reads that map and places values without decoding levels, so it runs two warps rather than the level-decoding kernel's three: a delta producer and a value writer. The writer trails the producer by one batch, gated on `next_pass_start_idx()`. That lag is what lets the two warps run concurrently in one phase instead of two phases split by a barrier. The loop therefore exits only when neither side can advance: gating the writer means a malformed page can leave `nz_count` permanently above anything the delta stream can supply. `decode_delta_binary_kernel` is untouched, including its name. Routing happens through `non_nz_map_page_mask`, seeded on the host with the caller's page mask and then cleared by the producer for every page it claims. The two kernels therefore partition the pages because the producer's claim *is* the routing decision, not because a second kernel re-derives it -- had it been re-derived, the two could disagree and a page would be decoded twice or not at all. The buffer is shared, so the further producers in this series clear their own claims into it; a page has exactly one map kind, so the writes are disjoint. For that partition to hold the consumer must not silently skip a page for any *additional* reason, so the conditions the host already decides are documented rather than re-tested. The one that cannot be decided on the host -- a claimed page the producer wrote no count for -- is a `cudf_assert`, which catches it in a debug build and compiles out in release. It is unreachable today: the producer runs over a superset of the pages this kernel decodes. `classify_nz_map_kind` names the encodings a consumer has been written for, which is DELTA_BINARY_PACKED alone, and widens by one enumerator as each remaining consumer lands. Claiming a page is what moves it off the level-decoding kernel -- a claimed page carries a non-null `nz_map`, and that is what routes it -- so the classifier names only the encodings that have somewhere to go. A flat DELTA_BYTE_ARRAY page is equally decodable from a rank map and is claimed once its consumer lands. Stating that in the classifier rather than in a separate encoding mask keeps one rule instead of two that have to agree. The page mask is kept, rather than testing `has_nz_map()` inside `decode_delta_binary_kernel` directly, so that kernel stays byte-identical while the feature is opt-in -- turning the env var off is then a true rollback. Both forms would read the same host-set fields, so this is not about the two disagreeing. The in-code TODO records when to collapse it. The producer gets its own stream and its own `cuda::event` rather than riding `fork_streams`' shared one, so that only the kernel that reads its output waits on it. The intent is that in a mixed file the PLAIN and dictionary decoders overlap with it rather than queueing behind it; that overlap is not measured here, since every benchmark below sets a single kernel mask. Measured on `parquet_read_delta_binary_nullable_page_sizes` and `parquet_read_delta_binary` (H100, clocks locked, feature off -> on): 50% nulls -25% required columns -4.8% 1% nulls break-even The win scales with how much level-decoding work the map removes. At 50% nulls the bit-packed level walk it replaces is expensive; on required columns no map is allocated at all and the gain is the narrower block alone. At 1% nulls the levels are a cheap RLE run, so the map's own traffic -- 4 bytes per value written, 4 per valid value read, against levels at 1-2 bytes per value -- costs about what it saves. Narrowing the map's indices is the fix for that, and is tracked for before the default flips. Validation: PARQUET_TEST 563 passed / 1 pre-existing skip and HYBRID_SCAN_TEST 105/105, both with the nz map off and on. This is the first PR in the series where the enabled arm decodes anything, so it is also the first real exercise of the nz map under hybrid scan. The test's env-var guard now restores any pre-existing value instead of unsetting it. Unsetting meant that running the suite with `LIBCUDF_PARQUET_NZ_MAP=1` -- which is how this feature is validated -- silently disabled it for every test after this one, the second of 129 in the file. Measured over a full run: 758 of 1723 subpasses saw the feature enabled before the fix, 1721 after. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

vyasr · 2026-10-08T04:30:36Z

/ok to test

coderabbitai · 2026-10-08T05:32:16Z

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cpp/src/io/parquet/decode_preprocess.cu
cpp/src/io/parquet/parquet_gpu.hpp
cpp/src/io/parquet/reader_impl.cpp
cpp/tests/io/parquet_reader_test.cpp

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📝 Summary

Summary by CodeRabbit

Performance
- Improved Parquet reading for eligible flat columns encoded with DELTA_BINARY_PACKED, including nullable and required columns. Bounded reads that skip rows are also supported by this decoding path; other column types and encodings continue to use the standard path.
Tests
- Added checks confirming that optimized and standard decoding return matching results for full reads and bounded reads that skip rows, for nullable and required columns.

📝 Summary

Walkthrough

The Parquet reader now supports an opt-in flat nonzero-map path for eligible DELTA_BINARY pages. It builds maps before decoding and uses them to place decoded values. Other pages retain the existing level-decoding path.

Changes

Parquet nonzero-map decoding

Layer / File(s)	Summary
Map metadata and allocation `cpp/src/io/parquet/parquet_gpu.hpp`, `cpp/src/io/parquet/reader_impl_preprocess.cu`, `cpp/src/io/parquet/reader_impl_chunking.*`, `cpp/src/io/parquet/reader_impl.hpp`	Page metadata and subpass storage now use nz-map state. Preprocessing selects flat, non-repeated DELTA_BINARY pages and allocates map storage for eligible pages. The reader captures `LIBCUDF_PARQUET_NZ_MAP`, which defaults to disabled.
Flat map preprocessing `cpp/src/io/parquet/decode_preprocess.cu`, `cpp/src/io/parquet/parquet_gpu.hpp`	A preprocessing kernel builds valid-rank maps and validity bits for selected pages. Required pages store the range count without an identity map. Optional pages without definition levels receive a zero count.
DELTA_BINARY map decoding `cpp/src/io/parquet/page_delta_decode.cu`, `cpp/src/io/parquet/parquet_gpu.hpp`	The decoder uses nz-map positions for mapped pages and applies level decoding to pages in the complementary mask. The map-based kernel handles sliced pages and resumed decoding, and reports unsupported parameters or a data-stream overrun.
Reader scheduling and validation `cpp/src/io/parquet/reader_impl.cpp`, `cpp/tests/io/parquet_reader_test.cpp`	When eligible pages exist, the reader runs map preprocessing on a separate stream and makes the delta-binary decoder wait for completion. The regression test compares enabled and disabled full and bounded reads.

Priority: ➖ Normal

Estimated code review effort: 4 (Complex) | ~45 minutes

Change: Feature

Merge Risk: ⚪ Minimal · up to e9079

No merge-blocking issue was established for the opt-in Parquet decoding path; it is ready for normal checks.

Pre-merge checks | 4 | 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 46.67% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 15 functions across 9 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check		The title clearly identifies the main change: adding the flat non-zero map producer and its DELTA_BINARY consumer.
Description check		The description directly explains the nz-map producer and consumer, supported page types, configuration flag, tests, and performance results.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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🧹 Nitpick comments (1)

cpp/tests/io/parquet_reader_test.cpp (1)
103-114: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick win

Add a required column and a chunked read to NzMapMatchesLevelDecoder.

The comment on Line 104-105 says that the test claims a required column. The table has only one column, and that column is nullable. The test therefore does not run the identity-map path. On that path nz_idx is null, the producer sets nz_count = value_limit, and the consumer computes dst_pos = sp - first_row.

The test also does not use chunked_parquet_reader. In a chunked read, the producer runs again for each output chunk. Each run uses that chunk's skip_rows/num_rows, while the level buffers are sized from the pass range. A non-zero first_row is then possible on pages after the first page of the read. This path is new, and no test covers it.

Add these cases while the feature is opt-in:

A non-nullable DELTA_BINARY_PACKED column in the same table.

A chunked_parquet_reader read with a small chunk_read_limit and pass_read_limit. Concatenate the chunks and compare them with expected, once with LIBCUDF_PARQUET_NZ_MAP set to "0" and once with it set to "1".
♻️ Sketch for the required column
   cudf::test::fixed_width_column_wrapper<int32_t> const col{values, values + num_rows, valids};
-  auto const expected = table_view({col});
+  cudf::test::fixed_width_column_wrapper<int32_t> const req_col(values, values + num_rows);
+  auto const expected = table_view({col, req_col});
 
   auto input_metadata = cudf::io::table_input_metadata{expected};
   input_metadata.column_metadata[0].set_encoding(cudf::io::column_encoding::DELTA_BINARY_PACKED);
+  input_metadata.column_metadata[1].set_encoding(cudf::io::column_encoding::DELTA_BINARY_PACKED);
+  input_metadata.column_metadata[1].set_nullability(false);
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Review comment at @cpp/tests/io/parquet_reader_test.cpp around lines 103 - 114:
Update NzMapMatchesLevelDecoder to include a non-nullable DELTA_BINARY_PACKED
column alongside the nullable column, marking its metadata non-nullable. Add a
chunked_parquet_reader case with small chunk_read_limit and pass_read_limit,
concatenate the returned chunks, and compare with expected under both
LIBCUDF_PARQUET_NZ_MAP values "0" and "1".

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Nitpick comments:
Review comments at @cpp/tests/io/parquet_reader_test.cpp:
- Around line 103-114: Update NzMapMatchesLevelDecoder to include a non-nullable
DELTA_BINARY_PACKED column alongside the nullable column, marking its metadata
non-nullable. Add a chunked_parquet_reader case with small chunk_read_limit and
pass_read_limit, concatenate the returned chunks, and compare with expected
under both LIBCUDF_PARQUET_NZ_MAP values "0" and "1".

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cpp/src/io/parquet/decode_preprocess.cu
cpp/src/io/parquet/page_delta_decode.cu
cpp/src/io/parquet/parquet_gpu.hpp
cpp/src/io/parquet/reader_impl.cpp
cpp/src/io/parquet/reader_impl.hpp
cpp/src/io/parquet/reader_impl_chunking.cu
cpp/src/io/parquet/reader_impl_chunking.hpp
cpp/src/io/parquet/reader_impl_preprocess.cu
cpp/tests/io/parquet_reader_test.cpp

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"Claimed" was standing in for a plain fact the code already names: a page either has an nz map or it does not, and `has_nz_map()` is the predicate. The word also framed a selection rule as if pages were being contended for, when nothing competes for them -- `classify_nz_map_kind` names the encodings a consumer has been written for, and that is the whole decision. Comments and doxygen only; no behaviour change. The unrelated uses elsewhere in the reader are a different sense of the word and are left alone: a length that "claims more bytes than remain in the page", `reader_impl_dict_transcode` claiming ownership of a column, and the dictionary slot claims in chunk_dict.cu. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Conflict in page_delta_decode.cu's include block, against NVIDIA#24356's removal of redundant CUB and Thrust device includes. Kept <cuda/std/algorithm>, which this branch added for `cuda::std::lower_bound` in the nz map consumer's sliced-page prefix count, and dropped <thrust/transform_scan.h> with upstream -- the file has no thrust:: use.

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Inline comments:
Review comments at @cpp/src/io/parquet/page_delta_decode.cu:
- Around line 661-668: After the trailing block.sync() in the loop, check
whether s->progress.src_pos is less than s->progress.nz_count; if so, set the
DATA_STREAM_OVERRUN error on s->setup.error from one block thread. Preserve the
existing error_code propagation so the caller reports the malformed page.

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`decode_delta_binary_kernel_with_nz_map` stops once neither of its two warps can advance, which is what keeps a malformed page from spinning forever. But it then returned without an error, and the producer has already written the validity bits for the rows it had counted -- so a page whose delta stream holds fewer values than its definition levels call for read back as valid rows over output slots nothing ever wrote. The stopping condition already knows this happened, so reporting it is one comparison on thread 0 after the loop. It cannot fire on a well-formed page: the only other way out of the loop is the `while` condition, which requires `src_pos >= nz_count`. This does not make a malformed page decode correctly, which is not something the reader can do. It moves the failure from silently wrong data to a reported error. `decode_delta_binary_kernel` has the same gap by a different route -- its writer warp advances `src_pos` by a full batch whether or not the producer supplied those values, so it runs to completion and writes stale rolling-buffer entries. That is pre-existing and is left alone here, so the level-decoding path stays byte-identical while the nz map is opt-in. Worth closing separately. Raised by CodeRabbit on NVIDIA#24501. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

mhaseeb123 · 2026-10-08T18:18:12Z

+  // This check failing indicates that we somehow failed to write out the null map for a page with
+  // nulls entering this kernel.
+  cudf_assert(nz_count_in >= 0 && (not process_nulls || nz_idx != nullptr));


cudf_assert compiles out in release. Propagate error instead. Please replace for any other similar static_asserts as well if I missed any.

Suggested change

// This check failing indicates that we somehow failed to write out the null map for a page with

// nulls entering this kernel.

cudf_assert(nz_count_in >= 0 && (not process_nulls || nz_idx != nullptr));

// The producer must have written the map for every page routed to this kernel

if (nz_count_in < 0 or (process_nulls and nz_idx == nullptr)) {

if (block.thread_rank() == 0) {

set_error(static_cast<kernel_error::value_type>(decode_error::NZ_MAP_NOT_PRODUCED),

error_code);

}

return;

}

I intentionally chose a cudf_assert in this case because the error here would be exclusively developer error, not user error or an invalid file. I would actually advocate to remove this assertion altogether at the end of the PR chain. It's mostly handy for debugging right now, but in practice if we ever hit this condition and don't assert (i.e. if we leave it as a cudf_assert and have a release build) then our tests will fail because we'll have pages that don't get correctly processed. set_error is for user-facing errors.

Some of the later improvements I've made in response to your reviews (specifically around removing the new mask and the way that I simplified filtering pages) make this assertion really superfluous, so I'm just going to drop it altogether.

mhaseeb123 · 2026-10-08T18:18:13Z

+  // A second producer-written count, for map kinds that need one. Unused by `DELTA_FLAT`, whose
+  // consumer derives the null count from `nz_idx` and `nz_count` itself.
  int32_t aux_count{};


optional nit: Unused in this PR. Okay to keep it if the next PR will need it

Suggested change

// A second producer-written count, for map kinds that need one. Unused by `DELTA_FLAT`, whose

// consumer derives the null count from `nz_idx` and `nz_count` itself.

int32_t aux_count{};

Ah yeah I managed to make this PR pretty standalone but this snuck in. Yes, this field will be used in subsequent PRs. At this point I'd rather just leave it in.

Never mind, now that I'm making so many other edits to address the review I'll just drop it to keep this PR lean and self-contained.

mhaseeb123 · 2026-10-10T01:24:00Z

    auto const& chunk = pass.chunks[page.chunk_idx];
    // A masked-out page is never classified, so it is never selected and never allocated for.
-    if (_level_prepass_enabled) { page.prepass_family = classify_prepass_family(page, chunk); }
+    if (_nz_map_enabled) { page.map_kind = classify_nz_map_kind(page, chunk); }


Design question: Instead of a secondary page mask that also interacts with page_mask from hybrid scan (kinda confusing), can we just add a new decode_kernel_mask::DELTA_BINARY_NZ_MAP and set it on the pages selected here (like recently added dict transcode does for DICT_INT32)? Kernel selection then stays in one place: decode_delta_binary_kernel skips these pages via its mask_filter, and non_nz_map_page_mask, its seeding, the producer's store and the page mask swap all go away.

AI written suggestion below:

Suggested change

if (_nz_map_enabled) { page.map_kind = classify_nz_map_kind(page, chunk); }

if (_nz_map_enabled) {

page.map_kind = classify_nz_map_kind(page, chunk);

if (page.map_kind == nz_map_kind::DELTA_FLAT) {

page.kernel_mask = decode_kernel_mask::DELTA_BINARY_NZ_MAP;

}

}

OK, this question led me to a broader investigation. My original constraint when I was working through this stack was to not change the original kernels, which is why we wound up with this extra mask, and I had kept it separate to avoid modifying the existing mask for a few reasons. My intention was to switch over to directly using has_nz_map as a simple binary flag at the end of the PR stack once we removed the old kernels. However, I'm realizing that if I just relax my restriction a little I can switch the old kernels to also filter on that by adding

if (pages[page_idx].has_nz_map(nz_map_kind::DELTA_FLAT)) { return; }

Then we don't need the new mask at all. I had originally kept the new mask as an easier rollback path in case we had to roll back for any reason, but this small addition is easy enough to roll back and saves us the cost of the extra allocation.

Four points from review on NVIDIA#24501, with the intrinsic modernization held back so it can be measured on its own. Drop `null_count_back_copier` from `precompute_flat_nz_map_kernel`. The producer never writes a null count -- the only mention of one in the file was the copier's own declaration -- so it copied back the value `setup_local_page_info` initialized, which the consumer then overwrote. `precompute_flat_nz_map` takes `cudf::memory_resources` and seeds the page mask from `mr.get_temporary_mr()`. Behaviour is unchanged: the single-argument constructor captures the current device resource for temporaries, which is what the explicit `get_current_device_resource_ref()` was passing. What it buys is that the temporary resource is now the caller's to choose. `NzMapMatchesLevelDecoder` gains a required column. On that path the producer writes no `nz_idx` and the consumer synthesizes the identity map from the rank alone -- the test's comment claimed to cover it while the table held one nullable column, so it never ran. The same fixture now pins its page geometry through `max_page_fragment_size` and `max_page_size_rows` rather than inheriting the writer's defaults, so what it exercises does not move when those change. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Replaces `__ffs`, `__clz` and `__popc` in `precompute_flat_nz_map_kernel` with `cuda::std::countr_zero`, `bit_width` and `popcount`, per review on NVIDIA#24501. The same file already called `cuda::std::countr_zero` for the list-lane scan, so it was inconsistent with itself. The guard had to change with it. `__ffs(mask) - 1` yields -1 on an empty mask, which `write_start >= 0` relied on; `countr_zero` yields `warp_size` instead, so the test is now `write_start < warp_size`. Keeping the old comparison would have sent every warp with no lane in range into the store with `write_start == 32`. `warp_size - __clz(mask)` is exactly `bit_width(mask)`. Separate from the review commit before it because it changes generated code and so needed its own measurement. The SASS is not identical -- normalized over both `level_t` instantiations it goes from 3878 to 3829 instructions, with `FLO.U32.SH` becoming `FLO.U32` plus a negate -- but that does not reach the clock: interleaved A/B, 3 rounds, H100 GPU 2 locked at 1755 MHz, parquet_read_delta_binary_nullable_page_sizes with the nz map enabled nullable_1, page_rows 256 1.003 nullable_1, page_rows 32 1.005 nullable_50, page_rows 256 1.007 nullable_50, page_rows 32 1.007 geomean 1.005 Within-arm spread is 0.3-3.1%, so a 0.5% geomean is a wash rather than a regression -- and the 49 instructions it removes buy nothing either, which says the producer's loop is not issue-bound. Measured on the nullable benchmark because `parquet_read_delta_binary` builds required columns, where the producer returns before reaching the loop these intrinsics are in. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

…d mask Both delta kernels now test the page's own nz map, so `non_nz_map_page_mask` and everything that fed it are gone: the per-subpass `device_uvector<bool>`, the thrust fill/copy that seeded it from the caller's page mask, the producer's store clearing each entry, the span threaded through two signatures, and the page-mask swap in the launcher. What replaces all of it is one line in `decode_delta_binary_kernel`: if (pages[page_idx].has_nz_map(nz_map_kind::DELTA_FLAT)) { return; } The consumer already routed this way. The mask existed only so the level-decoding kernel could be left untouched, and the page mask it already consults was the one channel available for telling it which pages another kernel had taken. That made `page_mask` carry two unrelated meanings -- pruned by hybrid scan, and claimed by the consumer -- which is the interaction review called confusing. It means pruned again, and the map alone decides routing. The launcher keeps a `bool has_flat_nz_map` where the span was, since it still has to decide whether the consumer has any work; both kernels now receive the caller's page mask unmodified. `decode_delta_binary_kernel` is therefore no longer byte-identical, which the previous commit in this branch leaned on. It gains one branch, and the rollback it was protecting is unaffected: with the feature off no page carries a map, so `has_nz_map()` is false everywhere and the branch is never taken. The mask seeding was the only allocation in `precompute_flat_nz_map`, so the `cudf::memory_resources` parameter added for it earlier in this branch has nothing left to serve and is removed, along with the thrust and rmm includes it needed. Validation: PARQUET_TEST 563 passed / 1 pre-existing skip and HYBRID_SCAN_TEST 105/105, both with the nz map off and on. An nsys trace over a LIST delta page and a flat one confirms the partition still holds with no mask: the level-decoding kernel runs for the pages the classifier declines, the consumer for the pages it selects. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Two defects found reviewing the branch as a whole. The truncated-stream report added earlier on this branch ORs its code onto `s->setup.error` without checking whether that is already set. A page that fails `setup_local_page_info` never enters the value loop, so `src_pos` stays 0 and the test fires: the reader returns `EMPTY_PAGE | DATA_STREAM_OVERRUN` with the nz map on and `EMPTY_PAGE` with it off, for the same file. Now reported only when nothing else is. `decode_delta_binary_kernel_with_nz_map` carried `skipped_leaf_values` handling copied from the level-decoding kernel, where it is already dead -- `setup_local_page_info` zeroes it for any page without repetition, which is what `classify_nz_map_kind` requires. It is also wrong for this kernel's data model: `nz_count` counts from page position 0, so a rank already spans the prefix below `first_row`, and `value_at(sp + skipped_leaf_values)` would have asked for that prefix twice. The resume branch, the batch-size special case, the `target_pos` subtraction and the index offset are gone, with the invariant stated where the decode index is set up. Also removed: a comment claiming the producer clears this page from a mask, which described machinery deleted in the previous commit; a comment asserting the level-decoding path "stays untouched", which stopped being true when it gained its routing branch; a `__popc` the earlier modernization missed, one line below its replaced sibling; an include left unused when the memory resource parameter went away; and three `block.sync()` calls that each follow a thread-0 write to global memory with nothing after them in the block. `num_claimed` becomes `num_mapped`, which the prose sweep had already done everywhere except this identifier. Validation: PARQUET_TEST 563 passed / 1 pre-existing skip and HYBRID_SCAN_TEST 105/105, both with the nz map off and on. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

… reach `NzMapMatchesLevelDecoder` read one nullable and one required flat column, which left four paths unexercised. An optional column with no null in it. `maybe_has_nulls` short-circuits on a definition-level stream that is one repeated run at the max level, so the producer takes its `!should_process_nulls` return with `nz_idx` allocated and the null mask left to the all-valid fill. The previous validity pattern put a null in every page, so this never ran. A nested column, which `classify_nz_map_kind` declines. Its pages stay on the level-decoding kernel while the flat columns go to the consumer, so the two kernels now partition the pages of one file inside a test rather than only in an nsys trace. A chunked read. The producer runs once per output chunk over the same scratch, each time with that chunk's row range rather than the pass's. A slice landing mid-page. The bounded read skipped 1001 rows against 1000-row pages, leaving `first_row` at 1, so the consumer's prefix search had a single value below it; at 1500 it has 500. The chunked comparison uses TABLES_EQUIVALENT because `cudf::concatenate` drops an all-true validity mask, so the all-valid column comes back non-nullable while the expected table is nullable. The values are identical. Not covered: `level_type_size == 2`, which needs a max definition or repetition level of 256 and so around that many levels of nesting. The `uint16_t` instantiation of the producer is unreachable in practice for the same reason. Validation: PARQUET_TEST 563 passed / 1 pre-existing skip and HYBRID_SCAN_TEST 105/105, both with the nz map off and on. An nsys trace of the test confirms the producer, the consumer and the level-decoding kernel all run. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

…ter loop `ni.data_out` reaches the output through a `PageNestingDecodeInfo*` that may point at the shared nesting cache or at global memory, and the store it feeds writes through that same pointer, so the compiler cannot prove the store does not alias `ni` and reloads it on every value. In SASS that is a generic `LD.E.64` per value, plus shared loads of `first_row` and `dtype_len` and a switch dispatching on a value it has just reloaded. The producer already hoists `valid_map` and `valid_map_offset` for the same reason; this brings the consumer in line. Performance-neutral, which is the claim being made here -- not a speedup. Interleaved A/B on `parquet_read_delta_binary_nullable_page_sizes` with the nz map enabled, H100 clock-locked at 1755 MHz, 6 rounds with the arm order alternating per round: geomean 0.9954, with the hoist faster in 14 of 24 paired rounds. Register count is unchanged at 40 and neither arm spills, so occupancy is not involved either way. The ordering mattered more than the change did. An earlier run of the same comparison put the hoist 1.9% behind, but it ran the arms in a fixed order every round, and re-running with the order alternating shows the sign following the order rather than the code: 1.0032 when the unhoisted arm ran first, 0.9877 when the hoisted arm did. Whichever arm runs second measures worse by about 1.5% on this benchmark. The apparent regression was an artifact of the harness. Validation: PARQUET_TEST 563 passed / 1 pre-existing skip and HYBRID_SCAN_TEST 105/105, both with the nz map off and on. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

`decode_delta_binary_kernel` skipped any page carrying an nz map, while the kernel that picks those pages up was launched only when the host's `has_flat_nz_map` was also true. Two derivations of the same decision: the host scan requires the env var and `classify_nz_map_kind` requires `kernel_mask & DELTA_BINARY`, the device skip requires neither. They agree today, and by construction rather than by luck -- a page only gets a map when both of those hold, so the host scan cannot be false while a page is mapped. But nothing makes that structural, and the window between `allocate_level_decode_space` and `decode_page_data` already contains a `kernel_mask` rewriter in `maybe_transcode_dict_pages`. If the two ever part, the page is decoded by neither kernel and no error is raised, and because the null mask is filled all-valid beforehand, the uninitialized output reads back as valid values rather than as nulls. Passing the launch flag into the kernel makes the skip conditional on it, so the two cannot disagree. When it is false the level-decoding kernel takes every page, which it decodes correctly: it walks definition levels and never consults the map. This also removes the one way the consumer could meet a page whose producer never ran. `nz_count` is seeded to -1 and is signed, so both the loop condition and the truncated-stream check would read false and the kernel would emit nothing and report nothing, leaving only a `cudf_assert` that compiles out in release. That state is now unreachable rather than merely unreached. Validation: PARQUET_TEST 563 passed / 1 pre-existing skip and HYBRID_SCAN_TEST 105/105, both with the nz map off and on. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

The consumer's `cudf_assert` on `nz_count`. Gating both routing decisions on one flag made the state it checked unreachable rather than merely unreached, so there is nothing left for it to catch. It had also drawn a review suggestion to report the condition through `set_error` instead, which would have been wrong in a way worth recording: every `decode_error` names something about the file, and the reader surfaces them as "Parquet data decode failed", so using that channel for a producer-consumer disagreement would have told a user their data was corrupt to report a bug in cuDF. `page_nz_map::aux_count`. Nothing writes or reads it. The branch that eventually needs it writes and reads it inside a single kernel, where it is a local as well; it becomes cross-kernel state only with the list producer. It can come back then, with the code that uses it. The producer's `first_row` clamp. `min(s->setup.first_row, decoded_value_limit)` guarded against the requested first row running past the page's decoded levels, which cannot happen: the level buffer is sized over the pass's row range and a read's range is a subrange of it. The consumer uses `first_row` unclamped for both the prefix search and the output position, so the clamp also left the two kernels nominally working from different values, resolved only by its being a no-op. Replaced with the invariant it was standing in for, stated once. Validation: PARQUET_TEST 563 passed / 1 pre-existing skip and HYBRID_SCAN_TEST 105/105, both with the nz map off and on. The chunked read added earlier in this branch is the case that would notice the clamp, since it re-runs the producer per output chunk with that chunk's row range against a pass-sized level buffer. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

…ucer-delta-binary

github-actions Bot assigned vyasr Oct 8, 2026

github-actions Bot added the libcudf Affects libcudf (C++/CUDA) code. label Oct 8, 2026

vyasr added feature request New feature or request non-breaking Non-breaking change cuIO cuIO issue Performance Performance related issue labels Oct 8, 2026

vyasr force-pushed the nz-map/02-flat-producer-delta-binary branch from 4499d99 to cf796a2 Compare October 8, 2026 04:16

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Comment thread cpp/src/io/parquet/page_delta_decode.cu

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Merge remote-tracking branch 'upstream/main' into nz-map/02-flat-prod…

4c32ea1

…ucer-delta-binary

-  // This check failing indicates that we somehow failed to write out the null map for a page with
-  // nulls entering this kernel.
-  cudf_assert(nz_count_in >= 0 && (not process_nulls || nz_idx != nullptr));
+  // The producer must have written the map for every page routed to this kernel
+  if (nz_count_in < 0 or (process_nulls and nz_idx == nullptr)) {
+    if (block.thread_rank() == 0) {
+      set_error(static_cast<kernel_error::value_type>(decode_error::NZ_MAP_NOT_PRODUCED),
+                error_code);
+    }
+    return;
+  }

	// A second producer-written count, for map kinds that need one. Unused by `DELTA_FLAT`, whose
	// consumer derives the null count from `nz_idx` and `nz_count` itself.
	int32_t aux_count{};

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Renamed from "prepass" to "nz map"

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