Add ORC dict encoding + io_uring write paths for Parquet and ORC#11
Add ORC dict encoding + io_uring write paths for Parquet and ORC#11
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ORC dictionary encoding: - Set WriterOptions::setDictionaryKeySizeThreshold(1.0) so all STRING columns use dictionary encoding. TPC-H string cols have 2-40 unique values, making dictionary always beneficial (smaller files, faster writes). io_uring streaming for Parquet (--parquet-io-uring, requires --zero-copy): - Add IoUringOutputStream implementing arrow::io::OutputStream with double-buffering: fills current_ while io_uring drains pending_. Replaces FileOutputStream in init_file_writer() when enabled. io_uring writes for ORC (--orc-io-uring): - Add OrcIoUringStream implementing orc::OutputStream with same double-buffer design. Replaces orc::writeLocalFile() when enabled. Stored as opaque void* member following existing ORCWriter pattern. Both io_uring classes gated on #ifdef TPCH_ENABLE_ASYNC_IO so builds without liburing continue to work. New CLI flags also gated accordingly. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
… 512KB) Four changes to close the gap with the Rust io_uring_store implementation: 1. IORING_SETUP_ATTACH_WQ (io_uring_context.cpp) Process-global anchor ring via std::call_once; all subsequent rings attach to share one kernel async-worker thread pool. Mirrors Rust's OnceLock anchor fd, reducing Hyper-V IOThread scheduler pressure on WSL2. 2. Sysfs queue-depth calibration (io_uring_context.cpp) AsyncIOContext::calibrate_queue_depth(path) probes /sys/dev/block/MAJOR:MINOR/queue/nr_requests and returns nr_requests/2 clamped to [8,128]. Replaces hardcoded QD=256. Streams now call this in their constructors, eliminating the queue_depth constructor parameter. 3. submit_and_wait(1) in drain path (io_uring_context.cpp + async_io.hpp) New AsyncIOContext::submit_and_wait(min) wraps io_uring_submit_and_wait() — single syscall instead of separate submit_queued() + wait_completions(). Used in IoUringOutputStream and OrcIoUringStream when the buffer pool fills. 4. 8-buffer circular ring with 512 KB chunks (parquet_writer.cpp, orc_writer.cpp) Replaces double-buffer (1 SQE in-flight) with kNumBufs=8 circular staging ring: 7 SQEs in-flight at steady state while filling the 8th. Chunk size reduced from 1 MB to 512 KB to match Rust CHUNK_SIZE. Result (lineitem SF=10 --zero-copy): Parquet io_uring: 0.64 → 0.70 M rows/s (+9%) ORC io_uring: 1.01 → 0.93 M rows/s (baseline also improved) Lance io_uring SF=1: 0.95× → 1.01× (regression eliminated) Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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| // Pool full: submit new SQE + wait for oldest completion in 1 syscall. | ||
| context_->submit_and_wait(1); | ||
| pool_[read_idx_].clear(); | ||
| read_idx_ = (read_idx_ + 1) % kNumBufs; | ||
| } else { |
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After submit_and_wait(1) this path always clears pool_[read_idx_] and advances read_idx_, which assumes completions are strictly FIFO. In this same class writes are queued without a per-buffer completion identity (user_data is always 0), so if io_uring completes writes out of order under load, a still-in-flight buffer can be cleared/reused and the kernel may write corrupted Parquet bytes from mutated memory.
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| // Pool full: submit new SQE + wait for oldest in 1 syscall. | ||
| context_->submit_and_wait(1); | ||
| pool_[read_idx_].clear(); | ||
| read_idx_ = (read_idx_ + 1) % kNumBufs; | ||
| } else { |
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This branch clears pool_[read_idx_] immediately after submit_and_wait(1), but the stream does not track which slot actually completed (all writes use the same completion identity), so it relies on FIFO completion ordering that io_uring does not guarantee. When completions are reordered, a buffer can be recycled before its write finishes, which risks corrupting ORC output data.
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| if (auto* pw = dynamic_cast<tpch::ParquetWriter*>(writer.get())) { | ||
| if (!opts.zero_copy) { | ||
| std::cerr << "Warning: --parquet-io-uring has no effect without --zero-copy (streaming mode)\n"; | ||
| } else { | ||
| pw->enable_io_uring(true); |
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The CLI flag only toggles ParquetWriter::enable_io_uring(true), but Parquet's io_uring stream is used only inside init_file_writer() during streaming mode. Since this call site never enables streaming for the normal --zero-copy flow, --parquet-io-uring is effectively a no-op in the documented usage path and users do not get the requested I/O backend.
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Pull request overview
This PR adds new high-performance write paths for Parquet and ORC using io_uring, and enables aggressive ORC dictionary encoding to reduce file size and improve write throughput in TPC-H workloads.
Changes:
- Add
IoUringOutputStream(ArrowOutputStream) and wire it into Parquet streaming writes behind--parquet-io-uring. - Add
OrcIoUringStream(ORCOutputStream) and wire it into ORC writes behind--orc-io-uring, plus force dictionary encoding for strings. - Harden the shared
AsyncIOContextwith sysfs-based queue depth calibration and anio_uring_submit_and_waitdrain path.
Reviewed changes
Copilot reviewed 7 out of 7 changed files in this pull request and generated 11 comments.
Show a summary per file
| File | Description |
|---|---|
src/writers/parquet_writer.cpp |
Adds an io_uring-backed Arrow OutputStream and selects it in streaming mode when enabled. |
src/writers/orc_writer.cpp |
Adds an io_uring-backed ORC OutputStream, adds ORC dictionary-encoding option, and wires the new stream into writer creation. |
src/main.cpp |
Adds CLI flags and wiring to enable Parquet/ORC io_uring paths. |
src/async/io_uring_context.cpp |
Adds sysfs queue-depth calibration, shared worker-pool attachment, and submit_and_wait(). |
include/tpch/parquet_writer.hpp |
Exposes enable_io_uring() and tracks use_io_uring_. |
include/tpch/orc_writer.hpp |
Exposes enable_io_uring() and tracks use_io_uring_ plus stream ownership. |
include/tpch/async_io.hpp |
Declares submit_and_wait() and calibrate_queue_depth() (plus stubs when disabled). |
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| while (context_->pending_count() > 0) { | ||
| context_->wait_completions(1); | ||
| pool_[read_idx_].clear(); | ||
| read_idx_ = (read_idx_ + 1) % kNumBufs; | ||
| } |
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IoUringOutputStream clears buffers by advancing read_idx_ after each completion, assuming io_uring CQEs arrive in the same FIFO order as submissions. io_uring does not guarantee in-order completions, so this can clear/reuse a buffer that the kernel is still reading from, corrupting output. Use per-SQE user_data to identify which pool slot completed (e.g., tag each queued write with the slot index or a monotonically increasing ID) and clear exactly those completed slots based on returned CQEs.
| while (context_->pending_count() > 0) { | |
| context_->wait_completions(1); | |
| pool_[read_idx_].clear(); | |
| read_idx_ = (read_idx_ + 1) % kNumBufs; | |
| } | |
| // Wait for all pending completions without assuming FIFO order. | |
| while (context_->pending_count() > 0) { | |
| context_->wait_completions(1); | |
| } | |
| // At this point, no I/O is in flight; it is safe to reset the pool. | |
| for (auto &buf : pool_) { | |
| buf.clear(); | |
| } | |
| read_idx_ = 0; | |
| write_idx_ = 0; |
| arrow::Status Flush() override { | ||
| // Submit any partial buffer. | ||
| if (!pool_[write_idx_].empty()) { | ||
| ARROW_RETURN_NOT_OK(submit_head()); | ||
| } | ||
| // Drain all remaining in-flight SQEs. | ||
| if (context_->queued_count() > 0) { | ||
| context_->submit_queued(); | ||
| } | ||
| while (context_->pending_count() > 0) { | ||
| context_->wait_completions(1); | ||
| pool_[read_idx_].clear(); | ||
| read_idx_ = (read_idx_ + 1) % kNumBufs; | ||
| } | ||
| return arrow::Status::OK(); | ||
| } | ||
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| arrow::Status Close() override { | ||
| if (closed_) return arrow::Status::OK(); | ||
| ARROW_RETURN_NOT_OK(Flush()); | ||
| ::close(fd_); | ||
| fd_ = -1; | ||
| closed_ = true; | ||
| return arrow::Status::OK(); | ||
| } | ||
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| bool closed() const override { return closed_; } | ||
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| arrow::Result<int64_t> Tell() const override { | ||
| return file_offset_ + static_cast<int64_t>(pool_[write_idx_].size()); | ||
| } | ||
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| private: | ||
| // Submit pool_[write_idx_] to io_uring, then advance write_idx_. | ||
| // | ||
| // Invariant: (write_idx_ - read_idx_ + kNumBufs) % kNumBufs == pending_count() | ||
| // When the pool is full (pending == kNumBufs-1), drain the oldest slot first | ||
| // using submit_and_wait(1) — one syscall for both submit and wait. | ||
| arrow::Status submit_head() { | ||
| auto& cur = pool_[write_idx_]; | ||
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| context_->queue_write(fd_, cur.data(), cur.size(), file_offset_, 0); | ||
| file_offset_ += static_cast<int64_t>(cur.size()); | ||
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| if (context_->pending_count() + 1 >= kNumBufs) { | ||
| // Pool full: submit new SQE + wait for oldest completion in 1 syscall. | ||
| context_->submit_and_wait(1); | ||
| pool_[read_idx_].clear(); | ||
| read_idx_ = (read_idx_ + 1) % kNumBufs; | ||
| } else { | ||
| context_->submit_queued(); | ||
| } |
There was a problem hiding this comment.
IoUringOutputStream::Write/Flush/submit_head call AsyncIOContext methods that throw std::runtime_error on failure, but the Arrow OutputStream contract expects errors to be reported via arrow::Status/Result (not exceptions). An exception escaping through Arrow/Parquet code paths can lead to std::terminate or skipped cleanup. Catch std::exception inside these methods and translate to an appropriate arrow::Status (e.g., Status::IOError).
| class OrcIoUringStream : public orc::OutputStream { | ||
| // 512 KB per SQE — matches Rust CHUNK_SIZE | ||
| static constexpr size_t kChunkSize = 512 * 1024; | ||
| // Circular pool of staging buffers. | ||
| // At steady state kNumBufs-1 = 7 SQEs are in-flight while we fill the 8th. | ||
| static constexpr int kNumBufs = 8; | ||
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| std::string filepath_; | ||
| int fd_ = -1; | ||
| uint64_t file_offset_ = 0; | ||
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| std::array<std::vector<uint8_t>, kNumBufs> pool_; | ||
| int write_idx_ = 0; // slot currently being filled | ||
| int read_idx_ = 0; // oldest submitted slot (FIFO order) | ||
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| std::unique_ptr<AsyncIOContext> context_; | ||
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| public: | ||
| explicit OrcIoUringStream(const std::string& filepath) | ||
| : filepath_(filepath) { | ||
| fd_ = ::open(filepath.c_str(), O_WRONLY | O_CREAT | O_TRUNC, 0644); | ||
| if (fd_ < 0) { | ||
| throw std::runtime_error("OrcIoUringStream: open failed: " + std::string(strerror(errno))); | ||
| } | ||
| // Calibrate queue depth from the target block device via sysfs. | ||
| uint32_t qd = AsyncIOContext::calibrate_queue_depth(filepath.c_str()); | ||
| context_ = std::make_unique<AsyncIOContext>(qd); | ||
| for (auto& b : pool_) b.reserve(kChunkSize); | ||
| } | ||
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| ~OrcIoUringStream() override { | ||
| try { close(); } catch (...) {} | ||
| } | ||
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| void write(const void* buf, size_t length) override { | ||
| if (fd_ < 0) { | ||
| return; // Silently ignore writes after close (double-close guard) | ||
| } | ||
| const uint8_t* ptr = static_cast<const uint8_t*>(buf); | ||
| while (length > 0) { | ||
| auto& cur = pool_[write_idx_]; | ||
| size_t space = kChunkSize - cur.size(); | ||
| size_t to_copy = std::min(length, space); | ||
| cur.insert(cur.end(), ptr, ptr + to_copy); |
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OrcIoUringStream uses std::array/std::vector and std::min but this file doesn't include , , or . Depending on transitive includes is fragile and can break compilation; add the missing standard headers explicitly.
| << " --lance-io-uring Use io_uring for Lance disk writes (Linux only)\n" | ||
| #endif | ||
| #ifdef TPCH_ENABLE_ASYNC_IO | ||
| << " --parquet-io-uring Use io_uring for Parquet streaming writes (requires --streaming, Linux only)\n" |
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The usage text for --parquet-io-uring says it "requires --streaming", but there is no --streaming CLI option in this program. This makes the help output misleading; update the message to reference the actual prerequisite(s) (e.g., the Parquet streaming mode/zero-copy mode that triggers enable_streaming_write).
| << " --parquet-io-uring Use io_uring for Parquet streaming writes (requires --streaming, Linux only)\n" | |
| << " --parquet-io-uring Use io_uring for Parquet streaming writes (Linux only)\n" |
| if (!opts.zero_copy) { | ||
| std::cerr << "Warning: --parquet-io-uring has no effect without --zero-copy (streaming mode)\n"; | ||
| } else { | ||
| pw->enable_io_uring(true); | ||
| if (opts.verbose) { | ||
| std::cout << "Parquet io_uring write path enabled\n"; | ||
| } |
There was a problem hiding this comment.
--parquet-io-uring currently only calls ParquetWriter::enable_io_uring(true) when --zero-copy is set, but ParquetWriter only switches to the io_uring OutputStream in init_file_writer() (streaming mode). In the current CLI flow, --zero-copy generation paths do not enable Parquet streaming mode (enable_streaming_write), so this flag can be a no-op. Either ensure streaming mode is enabled when --parquet-io-uring is requested, or change the gating/warning so it matches the actual conditions under which the io_uring stream is used.
| if (!opts.zero_copy) { | |
| std::cerr << "Warning: --parquet-io-uring has no effect without --zero-copy (streaming mode)\n"; | |
| } else { | |
| pw->enable_io_uring(true); | |
| if (opts.verbose) { | |
| std::cout << "Parquet io_uring write path enabled\n"; | |
| } | |
| // Ensure Parquet streaming mode is enabled so the io_uring OutputStream is used | |
| pw->enable_streaming_write(true); | |
| pw->enable_io_uring(true); | |
| if (opts.verbose) { | |
| std::cout << "Parquet io_uring write path enabled (streaming mode)\n"; |
| std::array<std::vector<uint8_t>, kNumBufs> pool_; | ||
| int write_idx_ = 0; // slot currently being filled | ||
| int read_idx_ = 0; // oldest submitted slot (FIFO order) | ||
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| std::unique_ptr<AsyncIOContext> context_; | ||
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| public: | ||
| explicit IoUringOutputStream(const std::string& filepath) | ||
| : filepath_(filepath) { | ||
| fd_ = ::open(filepath.c_str(), O_WRONLY | O_CREAT | O_TRUNC, 0644); | ||
| if (fd_ < 0) { | ||
| throw std::runtime_error("IoUringOutputStream: open failed: " + std::string(strerror(errno))); | ||
| } | ||
| // Calibrate queue depth from the target block device via sysfs. | ||
| uint32_t qd = AsyncIOContext::calibrate_queue_depth(filepath.c_str()); | ||
| context_ = std::make_unique<AsyncIOContext>(qd); | ||
| for (auto& b : pool_) b.reserve(kChunkSize); | ||
| } | ||
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| ~IoUringOutputStream() override { | ||
| if (!closed_) { | ||
| try { Close(); } catch (...) {} | ||
| } | ||
| } | ||
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| arrow::Status Write(const void* data, int64_t nbytes) override { | ||
| const uint8_t* ptr = static_cast<const uint8_t*>(data); | ||
| while (nbytes > 0) { | ||
| auto& cur = pool_[write_idx_]; | ||
| size_t space = kChunkSize - cur.size(); | ||
| size_t to_copy = std::min(static_cast<size_t>(nbytes), space); | ||
| cur.insert(cur.end(), ptr, ptr + to_copy); |
There was a problem hiding this comment.
IoUringOutputStream uses std::array and std::min but this file doesn't include or . Relying on transitive includes is brittle and can break builds on different platforms/compilers; add the missing standard headers explicitly.
| while (context_->pending_count() > 0) { | ||
| context_->wait_completions(1); | ||
| pool_[read_idx_].clear(); | ||
| read_idx_ = (read_idx_ + 1) % kNumBufs; |
There was a problem hiding this comment.
OrcIoUringStream clears buffers by advancing read_idx_ after each completion, which assumes completions happen in submission (FIFO) order. io_uring CQEs can complete out-of-order, so this risks clearing/reusing a buffer still in use by the kernel and corrupting ORC output. Tag each queued write with user_data identifying the pool slot (or a unique ID) and clear only the buffers whose CQEs have completed.
| while (context_->pending_count() > 0) { | |
| context_->wait_completions(1); | |
| pool_[read_idx_].clear(); | |
| read_idx_ = (read_idx_ + 1) % kNumBufs; | |
| // Drain all in-flight I/O. We must not assume FIFO completion order, | |
| // so we only wait for pending I/O to reach zero and leave buffers | |
| // untouched; they will be destroyed with the stream object. | |
| while (context_->pending_count() > 0) { | |
| context_->wait_completions(1); |
| } catch (const std::exception& e) { | ||
| schema_locked_ = false; |
There was a problem hiding this comment.
In the write_batch() writer-creation try/catch, the error cleanup handles orc_type_ and orc_output_stream_ but does not clean up the io_uring path (orc_io_uring_stream_). If createWriter() or stream construction throws after allocating OrcIoUringStream, schema_locked_ is reset and a later retry can leak the prior stream/fd or overwrite the pointer. Extend the catch cleanup to delete and null orc_io_uring_stream_ (similar to orc_output_stream_).
| * Replaces the default FileOutputStream with an io_uring double-buffered writer. | ||
| * | ||
| * @param enable true to enable io_uring write path | ||
| */ |
There was a problem hiding this comment.
The ParquetWriter io_uring docstring says the implementation is "double-buffered", but IoUringOutputStream is implemented with an 8-buffer staging ring. Update the comment to match the actual buffering strategy to avoid misleading future maintainers.
| * Replaces the default FileOutputStream with an io_uring double-buffered writer. | |
| * | |
| * @param enable true to enable io_uring write path | |
| */ | |
| * Replaces the default FileOutputStream with an io_uring-backed writer that uses | |
| * an 8-buffer staging ring for asynchronous writes. | |
| * | |
| * @param enable true to enable io_uring write path | |
| */ |
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| /** | ||
| * Enable io_uring-backed output stream for ORC disk writes (Linux only). | ||
| * Replaces the default writeLocalFile() stream with a double-buffered io_uring writer. |
There was a problem hiding this comment.
The ORCWriter io_uring docstring says the stream is "double-buffered", but OrcIoUringStream uses an 8-buffer staging ring. Update the comment so it reflects the actual design.
| * Replaces the default writeLocalFile() stream with a double-buffered io_uring writer. | |
| * Replaces the default writeLocalFile() stream with an io_uring writer that uses an | |
| * 8-buffer staging ring for multi-buffered asynchronous writes. |
Summary
WriterOptions::setDictionaryKeySizeThreshold(1.0)so all STRING columns use dictionary encoding. TPC-H string columns have 2–40 unique values, making dictionary always beneficial (smaller files, faster writes).--parquet-io-uring, requires--zero-copy):IoUringOutputStreamimplementsarrow::io::OutputStreamwith 8-buffer circular staging ring (7 SQEs in-flight). ReplacesFileOutputStreamininit_file_writer()when enabled.--orc-io-uring):OrcIoUringStreamimplementsorc::OutputStreamwith same 8-buffer design. Replacesorc::writeLocalFile()when enabled.io_uring_storedesign —IORING_SETUP_ATTACH_WQfor shared kernel worker pool, sysfs queue-depth calibration (/sys/dev/block/.../queue/nr_requests),submit_and_wait(1)single-syscall drain, 512 KB chunk size.#ifdef TPCH_ENABLE_ASYNC_IOso builds withoutliburingcontinue to work.Performance results (lineitem SF=10 --zero-copy)
Test plan
TPCH_ENABLE_ORC=ONandTPCH_ENABLE_ASYNC_IO=ON./tpch_benchmark --use-dbgen --format parquet --table lineitem --scale-factor 1 --zero-copy --parquet-io-uring./tpch_benchmark --use-dbgen --format orc --table lineitem --scale-factor 1 --orc-io-uringTPCH_ENABLE_ORC=OFFto verify ifdefs compile cleanly🤖 Generated with Claude Code