adriangb commented on code in PR #10020: URL: https://github.com/apache/arrow-rs/pull/10020#discussion_r3344413618
########## parquet/src/column/page_store.rs: ########## @@ -0,0 +1,158 @@ +// Licensed to the Apache Software Foundation (ASF) under one +// or more contributor license agreements. See the NOTICE file +// distributed with this work for additional information +// regarding copyright ownership. The ASF licenses this file +// to you under the Apache License, Version 2.0 (the +// "License"); you may not use this file except in compliance +// with the License. You may obtain a copy of the License at +// +// http://www.apache.org/licenses/LICENSE-2.0 +// +// Unless required by applicable law or agreed to in writing, +// software distributed under the License is distributed on an +// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY +// KIND, either express or implied. See the License for the +// specific language governing permissions and limitations +// under the License. + +//! Pluggable storage for completed, serialized page blobs. +//! +//! While a row group is being written the [`ArrowWriter`] must buffer every +//! column's encoded pages, because Parquet requires each column chunk to be +//! contiguous on disk while record batches arrive with all columns interleaved. +//! By default that buffer lives on the heap, so the writer's peak memory grows +//! with the row group size. A [`PageStore`] lets the buffer live somewhere else +//! — a local temp file, object storage, etc. — bounding peak write memory +//! independently of the row group size. +//! +//! [`ArrowWriter`]: crate::arrow::arrow_writer::ArrowWriter + +use std::fmt::Debug; + +use bytes::Bytes; + +use crate::errors::{ParquetError, Result}; + +/// An opaque, store-allocated handle to a blob held by a [`PageStore`]. +/// +/// Handles are allocated by the store — densely and sequentially — and are only +/// meaningful to the store that produced them. The caller treats them as opaque +/// tokens and decides what they *mean* (ordering, which one is the dictionary +/// page, etc.). +/// +/// Letting the store allocate the handle (rather than the caller choosing keys) +/// lets each backend pick the cheapest possible locator with no hashing: an +/// in-memory backend uses the handle as an index into a `Vec`, a temp-file +/// backend as an index into a `Vec<(offset, len)>`, and so on. +#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)] +pub struct PageKey(pub(crate) u64); + +/// A pluggable store for completed, serialized page blobs. +/// +/// The store is intentionally "dumb": it only maps an opaque [`PageKey`] to a +/// blob of bytes. It knows nothing about pages, dictionaries, ordering, or +/// offsets. The caller keeps the handles it gets back from [`put`](Self::put) +/// and decides what they mean. +/// +/// Each store instance is owned by a single column writer and mutated by one +/// thread at a time (both methods take `&mut self`), so it needs no internal +/// synchronization — hence only `Send`, not `Sync`. +/// +/// The default ([`InMemoryPageStore`]) keeps blobs on the heap. Configure a +/// different backend via +/// [`ArrowWriterOptions::with_page_store_factory`](crate::arrow::arrow_writer::ArrowWriterOptions::with_page_store_factory). +pub trait PageStore: Send { + /// Store `value`, returning a handle that can later be passed to + /// [`take`](Self::take). + fn put(&mut self, value: Bytes) -> Result<PageKey>; + + /// Take back the blob previously stored under `key`. + /// + /// The caller takes ownership of the returned bytes and will **not** request + /// `key` again, so the store may release any resources backing it — eagerly + /// here, or when the store is dropped. + fn take(&mut self, key: PageKey) -> Result<Bytes>; +} + +/// Creates a fresh [`PageStore`] for each column chunk. +/// +/// See +/// [`ArrowWriterOptions::with_page_store_factory`](crate::arrow::arrow_writer::ArrowWriterOptions::with_page_store_factory). +pub trait PageStoreFactory: Send + Sync + Debug { + /// Create a new, empty [`PageStore`] for the leaf column at `column_index`. + /// + /// `column_index` is a hint a backend may use to e.g. name spill files or + /// shard across a bounded pool; it carries no ordering or coordination + /// requirement. + fn create(&self, column_index: usize) -> Result<Box<dyn PageStore>>; +} + +/// The default [`PageStore`], holding blobs on the heap in a `Vec<Bytes>`. +/// +/// This is byte-for-byte equivalent to the writer's historical buffering Review Comment: sorry about that. llms love to do that and I always have to steer them right (as I did here I think). -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
