feat: buffered reading of transaction logs #1549

eeroel · 2023-07-20T13:30:46Z

Description

This PR introduces two changes to how the commit log is read:

When reading the commit log, get requests are made concurrently in a buffered stream. This decreases latency when there are many files in the log since the last checkpoint.
Before scanning the log, the latest table version is found by listing with list_with_offset. This helps avoid a potential infinite loop in a slow reader/fast writer scenario, and makes it possible to buffer GET requests without making any unnecessary ones. This listing logic is now also used for the time-travel reading.

Related Issue(s)

Documentation

github-actions · 2023-07-20T13:31:15Z

ACTION NEEDED

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rtyler · 2023-07-20T14:13:52Z

rust/src/delta.rs

+
+        let buf_size = 50; // TODO
+
+        // why is mut needed here and is it OK?


To answer the question in the comment here, the mut is needed because of the log_buffer.next() below which will consume from the buffer

rtyler · 2023-07-20T14:49:09Z

rust/src/delta.rs

+        // why is mut needed here and is it OK?
+        let mut log_buffer = {
+            match max_version {
+                Some(n) => log_stream.take((n - self.version() + 2).try_into().unwrap()).buffered(buf_size),


Suggested change

Some(n) => log_stream.take((n - self.version() + 2).try_into().unwrap()).buffered(buf_size),

Some(n) => log_stream.take((n - self.version() + 2).try_into()?).buffered(buf_size),

I'm not sure off the top of my head, but I think the ? will work and help ensure that errors get propagated up to the DeltaResult returned by the function

This didn't work directly, but I added explicit handling for the error cases

rtyler · 2023-07-20T14:50:41Z

rust/src/delta.rs

+        };
+
+        while let Some((new_version, actions)) = {
+            let next_commit = log_buffer.next().await.unwrap();


Suggested change

let next_commit = log_buffer.next().await.unwrap();

let next_commit = log_buffer.next().await?;

This might be warranted as well, unwraps will panic the caller on errors which is not something we want

In this case the await returned an Option so I just handled it as such in the match below. Now the case when the stream ends before expected is explicitly an error

rust/tests/read_delta_test.rs

rtyler · 2023-07-21T07:04:23Z

rust/src/delta.rs

+/// TODO
+pub async fn open_table_with_version_and_log_buffer(
+    table_uri: impl AsRef<str>,
+    version: i64,
+    log_buffer_size: usize,
+) -> Result<DeltaTable, DeltaTableError> {
+    let table = DeltaTableBuilder::from_uri(table_uri)
+        .with_version(version)
+        .with_log_buffer_size(log_buffer_size)
+        .load()
+        .await?;
+    Ok(table)
+}
+


We have been discouraging more use of these top level methods, I would prefer this function not be added and instead users who are interested in buffering to use the table builder method

rtyler · 2023-07-21T07:04:53Z

rust/src/builder.rs

@@ -153,6 +169,12 @@ impl DeltaTableBuilder {
        self
    }

+    /// Sets `log_buffer_size` to the builder
+    pub fn with_log_buffer_size(mut self, log_buffer_size: usize) -> Self {


Suggested change

pub fn with_log_buffer_size(mut self, log_buffer_size: usize) -> Self {

pub fn with_buffer(mut self, log_buffer_size: usize) -> Self {

IMHO this can be more concise

eeroel · 2023-07-22T08:16:56Z

Did some refactoring and revisions according to suggestions, and also exposed the parameter to Python. Confirmed the speed-up locally against a table in S3, from_data_catalog takes 13s with no concurrency and <2s with log_buffer_size=30 (87 files in the log since the last checkpoint)

eeroel · 2023-07-22T13:05:10Z

rust/src/builder.rs

@@ -365,7 +388,7 @@ lazy_static::lazy_static! {
 /// Extra slashes will be removed from the end path as well.
 ///
 /// Will return an error if the location is not valid. For example,
-pub(crate) fn ensure_table_uri(table_uri: impl AsRef<str>) -> DeltaResult<Url> {
+pub fn ensure_table_uri(table_uri: impl AsRef<str>) -> DeltaResult<Url> {


This I figured might not be a good idea, but is there some other way of using the function in the test?

To keep it private, we can keep the tests within this file, in the tests section at the bottom.

Hmm, then I have some trouble with the mod fs_common where I put the SlowStore implementation. And the tests are not really testing builder per se. Would it make sense to just make a copy of this function in fs_common for the purposes of the test?

rtyler · 2023-07-22T21:48:17Z

rust/src/delta.rs

+                Some((v, Ok(x))) => Ok(Some((v, self.get_actions(v,  x.bytes().await?).await?))),
+                Some((_, Err(ObjectStoreError::NotFound { .. }))) => Ok(None),
+                Some((_, Err(err))) => Err(DeltaTableError::GenericError { source: Box::new(err) }),  // TODO ??
+                None => Err(DeltaTableError::Generic(String::from("Log stream closed unexpectedly!")))


My understanding is perhaps a bit hazy, but isn't a None at the end of the stream an expected condition? Won't this always happen once the stream is at the end?

Yeah you're right, this is expected. I made this an Ok case and also updated the .take call to take max_version - self.version() elements instead of +2. Had some confusion there earlier due to this error.

rtyler · 2023-07-22T21:50:11Z

rust/tests/fs_common/mod.rs

+pub struct SlowStore {
+    inner: DeltaObjectStore
+}


rtyler · 2023-07-22T21:52:01Z

rust/tests/read_delta_test.rs

+    let max_iter = 10;
+    let buf_size = 10;
+
+    let location = deltalake::builder::ensure_table_uri(path).unwrap();


I'm on the fence about letting this API leak out here, but let's roll with it for now

eeroel · 2023-07-23T04:35:43Z

rust/src/delta.rs

-        while let PeekCommit::New(new_version, actions) =
-            self.peek_next_commit(self.version()).await?
+        let max_version = max_version.and_then(|x| {
+            if x <= self.version() {


@rtyler I refactored this max_version handling a bit so it's clearer. Here I made explicit the behavior that's on main currently: i.e. the table will be updated to the latest version if max_version is smaller or equal to the current version.

eeroel · 2023-07-23T04:40:23Z

Did some refactoring and fixes and added a test to check that results are correct with different buffer sizes. I will still think a bit about how to limit the number of requests, as now there can be potentially a lot of unnecessary ones if max_version is not set

eeroel · 2023-07-23T14:43:03Z

rust/src/delta.rs

@@ -540,14 +550,78 @@ impl DeltaTable {
            self.version(),
        );

-        while let PeekCommit::New(new_version, actions) =
-            self.peek_next_commit(self.version()).await?
+        // update to latest version if given max_version is not larger than current version


@rtyler I ended up adding this bigger change to list the files to find out what the latest version is. The code is mostly copied over from another module so it needs refactoring. It's somewhat orthogonal to the buffered reading changes, but unless I'm missing something

it's necessary in order to make sure the load actually completes

it lets get requests to be buffered without creating any wasted requests (and thus the user doesn't need to be made aware of potential extra costs)

I understand though that this is a more major change because listing can be costly with big logs and in particular with no prefix filtering. And as far as I understood the protocol doesn't prescribe how to do this, but it does sort of hint at listing first being the way to read tables.

eeroel · 2023-09-08T10:25:09Z

Rebased on main

eeroel requested review from houqp, xianwill, wjones127, fvaleye, roeap, rtyler and mosyp as code owners July 20, 2023 13:30

github-actions bot added binding/rust Issues for the Rust crate rust labels Jul 20, 2023

rtyler marked this pull request as draft July 20, 2023 13:43

rtyler reviewed Jul 20, 2023

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eeroel commented Jul 21, 2023

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rust/tests/read_delta_test.rs Outdated Show resolved Hide resolved

rtyler reviewed Jul 21, 2023

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rtyler changed the title ~~(WIP) Feat/buffered log reading~~ feat: buffered reading of transaction logs Jul 21, 2023

rtyler self-assigned this Jul 21, 2023

eeroel force-pushed the feat/buffered_log_reading branch from e3a913c to 6c64eb2 Compare July 21, 2023 15:43

github-actions bot added the binding/python Issues for the Python package label Jul 22, 2023

eeroel force-pushed the feat/buffered_log_reading branch from c8e5a79 to e32d71f Compare July 22, 2023 06:28

eeroel requested a review from rtyler July 22, 2023 08:06

eeroel commented Jul 22, 2023

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rtyler reviewed Jul 22, 2023

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eeroel force-pushed the feat/buffered_log_reading branch from 4490249 to caa18f0 Compare July 23, 2023 04:31

eeroel commented Jul 23, 2023

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eeroel force-pushed the feat/buffered_log_reading branch 2 times, most recently from a7608d2 to b187374 Compare July 23, 2023 14:23

eeroel commented Jul 23, 2023

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eeroel force-pushed the feat/buffered_log_reading branch from 6da464f to c591971 Compare July 25, 2023 06:13

eeroel added 23 commits September 8, 2023 10:10

remove an unwrap

a402654

initial config, test

83d6881

refactor test

8b30341

expose to python

741f137

clean docs

6381c90

expose to python

8bade70

end of stream handling, more testing

69467ae

add test, limit for log buffer size

fc8e990

list files to get latest version

96fe14f

list from current

3e97d30

fix initializer in bench code

d6da3bf

use listing for get_latest_version

e7e120d

clean up

da3dbf1

some revisions

32db9ec

use dynamic data for test

e22a687

some revisions

8549127

update test file name

7f7ee6f

update python doc

eb386c0

format

fb3c8dd

satisfy linter

987e2a0

more formatting

e57e020

rename builder method

5dfdef4

yet more formatting

41cfafb

auto-merge was automatically disabled September 8, 2023 07:10
Head branch was pushed to by a user without write access

eeroel force-pushed the feat/buffered_log_reading branch from cfd41e5 to 41cfafb Compare September 8, 2023 07:10

wjones127 enabled auto-merge (squash) September 9, 2023 23:23

Merge branch 'main' into feat/buffered_log_reading

59e97cd

wjones127 merged commit eb36ddf into delta-io:main Sep 10, 2023
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Tom-Newton mentioned this pull request Aug 12, 2024

Transaction log parsing performance regression #2760

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feat: buffered reading of transaction logs #1549

feat: buffered reading of transaction logs #1549

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eeroel commented Sep 8, 2023


		let buf_size = 50; // TODO

		// why is mut needed here and is it OK?

	Some(n) => log_stream.take((n - self.version() + 2).try_into().unwrap()).buffered(buf_size),
	Some(n) => log_stream.take((n - self.version() + 2).try_into()?).buffered(buf_size),

	let next_commit = log_buffer.next().await.unwrap();
	let next_commit = log_buffer.next().await?;

	pub fn with_log_buffer_size(mut self, log_buffer_size: usize) -> Self {
	pub fn with_buffer(mut self, log_buffer_size: usize) -> Self {

feat: buffered reading of transaction logs #1549

feat: buffered reading of transaction logs #1549

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eeroel commented Jul 20, 2023 • edited Loading

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eeroel commented Jul 22, 2023 • edited Loading

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eeroel commented Jul 23, 2023 • edited Loading

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