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Posted to github@arrow.apache.org by "tustvold (via GitHub)" <gi...@apache.org> on 2023/04/10 16:12:03 UTC
[GitHub] [arrow-rs] tustvold opened a new pull request, #4046: Document Async decoder usage (#4043) (#78)
tustvold opened a new pull request, #4046:
URL: https://github.com/apache/arrow-rs/pull/4046
# Which issue does this PR close?
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Closes #4043
Closes #78
# Rationale for this change
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It isn't immediately obvious how to use these decoders in an async setting, so lets document it.
# What changes are included in this PR?
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[GitHub] [arrow-rs] tustvold commented on a diff in pull request #4046: Document Async decoder usage (#4043) (#78)
Posted by "tustvold (via GitHub)" <gi...@apache.org>.
tustvold commented on code in PR #4046:
URL: https://github.com/apache/arrow-rs/pull/4046#discussion_r1161861084
##########
arrow-csv/src/reader/mod.rs:
##########
@@ -39,6 +41,84 @@
//! let mut csv = Reader::new(file, Arc::new(schema), false, None, 1024, None, None, None);
//! let batch = csv.next().unwrap().unwrap();
//! ```
+//!
+//! # Async Usage
+//!
+//! The lower-level [`Decoder`] can be integrated with various forms of async data streams.
Review Comment:
The "various forms" here is key, the major problem with the async ecosystem is there is no one-size fits all async IO primitive, the intention behind the Decoder interface is to not be opinionated about where the bytes are coming from. This is similar to the AsyncFileReader trait we have for parquet, which similarly is not opinionated about what the underlying IO primitive actually is.
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[GitHub] [arrow-rs] tustvold commented on a diff in pull request #4046: Document Async decoder usage (#4043) (#78)
Posted by "tustvold (via GitHub)" <gi...@apache.org>.
tustvold commented on code in PR #4046:
URL: https://github.com/apache/arrow-rs/pull/4046#discussion_r1162538577
##########
arrow-csv/src/reader/mod.rs:
##########
@@ -39,6 +41,84 @@
//! let mut csv = Reader::new(file, Arc::new(schema), false, None, 1024, None, None, None);
//! let batch = csv.next().unwrap().unwrap();
//! ```
+//!
+//! # Async Usage
+//!
+//! The lower-level [`Decoder`] can be integrated with various forms of async data streams.
+//!
+//! For example, see below for how it can be used with an arbitrary `Stream` of `Bytes`
+//!
+//! ```
+//! # use std::task::{Poll, ready};
+//! # use bytes::{Buf, Bytes};
+//! # use arrow_schema::ArrowError;
+//! # use futures::stream::{Stream, StreamExt};
+//! # use arrow_array::RecordBatch;
+//! # use arrow_csv::reader::Decoder;
+//! #
+//! fn decode_stream<S: Stream<Item = Bytes> + Unpin>(
+//! mut decoder: Decoder,
+//! mut input: S,
+//! ) -> impl Stream<Item = Result<RecordBatch, ArrowError>> {
+//! let mut buffered = Bytes::new();
+//! futures::stream::poll_fn(move |cx| {
+//! loop {
+//! if buffered.is_empty() {
+//! if let Some(b) = ready!(input.poll_next_unpin(cx)) {
+//! buffered = b;
+//! }
+//! }
+//! let decoded = match decoder.decode(buffered.as_ref()) {
+//! // Note: the decoder needs to be called with an empty
+//! // array to delimit the final record
Review Comment:
The fallthrough of the branch above will end up here, I'll move it up to the match on poll_next_unpin to make it more clear
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[GitHub] [arrow-rs] crepererum commented on a diff in pull request #4046: Document Async decoder usage (#4043) (#78)
Posted by "crepererum (via GitHub)" <gi...@apache.org>.
crepererum commented on code in PR #4046:
URL: https://github.com/apache/arrow-rs/pull/4046#discussion_r1162528022
##########
arrow-csv/src/reader/mod.rs:
##########
@@ -39,6 +41,84 @@
//! let mut csv = Reader::new(file, Arc::new(schema), false, None, 1024, None, None, None);
//! let batch = csv.next().unwrap().unwrap();
//! ```
+//!
+//! # Async Usage
+//!
+//! The lower-level [`Decoder`] can be integrated with various forms of async data streams.
+//!
+//! For example, see below for how it can be used with an arbitrary `Stream` of `Bytes`
+//!
+//! ```
+//! # use std::task::{Poll, ready};
+//! # use bytes::{Buf, Bytes};
+//! # use arrow_schema::ArrowError;
+//! # use futures::stream::{Stream, StreamExt};
+//! # use arrow_array::RecordBatch;
+//! # use arrow_csv::reader::Decoder;
+//! #
+//! fn decode_stream<S: Stream<Item = Bytes> + Unpin>(
+//! mut decoder: Decoder,
+//! mut input: S,
+//! ) -> impl Stream<Item = Result<RecordBatch, ArrowError>> {
+//! let mut buffered = Bytes::new();
+//! futures::stream::poll_fn(move |cx| {
+//! loop {
+//! if buffered.is_empty() {
+//! if let Some(b) = ready!(input.poll_next_unpin(cx)) {
+//! buffered = b;
+//! }
+//! }
+//! let decoded = match decoder.decode(buffered.as_ref()) {
+//! // Note: the decoder needs to be called with an empty
+//! // array to delimit the final record
Review Comment:
Where is this done in this example? I would have expected that there's some `decoder.finish()` method instead of some sentinel value for this purpose (I've seen a similar API design w/ some compressor crates before).
##########
arrow-csv/src/reader/mod.rs:
##########
@@ -39,6 +41,84 @@
//! let mut csv = Reader::new(file, Arc::new(schema), false, None, 1024, None, None, None);
//! let batch = csv.next().unwrap().unwrap();
//! ```
+//!
+//! # Async Usage
+//!
+//! The lower-level [`Decoder`] can be integrated with various forms of async data streams.
Review Comment:
This information should be part of the doc-string, not hidden in some PR comment.
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[GitHub] [arrow-rs] tustvold merged pull request #4046: Document Async decoder usage (#4043) (#78)
Posted by "tustvold (via GitHub)" <gi...@apache.org>.
tustvold merged PR #4046:
URL: https://github.com/apache/arrow-rs/pull/4046
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[GitHub] [arrow-rs] tustvold commented on a diff in pull request #4046: Document Async decoder usage (#4043) (#78)
Posted by "tustvold (via GitHub)" <gi...@apache.org>.
tustvold commented on code in PR #4046:
URL: https://github.com/apache/arrow-rs/pull/4046#discussion_r1161861084
##########
arrow-csv/src/reader/mod.rs:
##########
@@ -39,6 +41,84 @@
//! let mut csv = Reader::new(file, Arc::new(schema), false, None, 1024, None, None, None);
//! let batch = csv.next().unwrap().unwrap();
//! ```
+//!
+//! # Async Usage
+//!
+//! The lower-level [`Decoder`] can be integrated with various forms of async data streams.
Review Comment:
The "various forms" here is key, one of the major challenges in accommodating the async ecosystem is there is no one-size fits all async IO primitive, the intention behind the Decoder interface is to not be opinionated about where the bytes are coming from. This is similar to the AsyncFileReader trait we have for parquet, which similarly is not opinionated about what the underlying IO primitive actually is.
--
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[GitHub] [arrow-rs] tustvold commented on a diff in pull request #4046: Document Async decoder usage (#4043) (#78)
Posted by "tustvold (via GitHub)" <gi...@apache.org>.
tustvold commented on code in PR #4046:
URL: https://github.com/apache/arrow-rs/pull/4046#discussion_r1162538577
##########
arrow-csv/src/reader/mod.rs:
##########
@@ -39,6 +41,84 @@
//! let mut csv = Reader::new(file, Arc::new(schema), false, None, 1024, None, None, None);
//! let batch = csv.next().unwrap().unwrap();
//! ```
+//!
+//! # Async Usage
+//!
+//! The lower-level [`Decoder`] can be integrated with various forms of async data streams.
+//!
+//! For example, see below for how it can be used with an arbitrary `Stream` of `Bytes`
+//!
+//! ```
+//! # use std::task::{Poll, ready};
+//! # use bytes::{Buf, Bytes};
+//! # use arrow_schema::ArrowError;
+//! # use futures::stream::{Stream, StreamExt};
+//! # use arrow_array::RecordBatch;
+//! # use arrow_csv::reader::Decoder;
+//! #
+//! fn decode_stream<S: Stream<Item = Bytes> + Unpin>(
+//! mut decoder: Decoder,
+//! mut input: S,
+//! ) -> impl Stream<Item = Result<RecordBatch, ArrowError>> {
+//! let mut buffered = Bytes::new();
+//! futures::stream::poll_fn(move |cx| {
+//! loop {
+//! if buffered.is_empty() {
+//! if let Some(b) = ready!(input.poll_next_unpin(cx)) {
+//! buffered = b;
+//! }
+//! }
+//! let decoded = match decoder.decode(buffered.as_ref()) {
+//! // Note: the decoder needs to be called with an empty
+//! // array to delimit the final record
Review Comment:
The fallthrough of the branch above will end up here
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