From 5d4b6f2173344d59d59c7f6336c5d21799f8b37d Mon Sep 17 00:00:00 2001
From: Alex Auvolat <alex@adnab.me>
Date: Mon, 19 Sep 2022 12:16:38 +0200
Subject: Faster GetObject workflow for getting entire objects

---
 src/api/s3/get.rs | 86 +++++++++++++++++++++++++++++++++----------------------
 1 file changed, 51 insertions(+), 35 deletions(-)

(limited to 'src/api/s3/get.rs')

diff --git a/src/api/s3/get.rs b/src/api/s3/get.rs
index ae4c287d..2a99551a 100644
--- a/src/api/s3/get.rs
+++ b/src/api/s3/get.rs
@@ -2,16 +2,19 @@
 use std::sync::Arc;
 use std::time::{Duration, UNIX_EPOCH};
 
-use futures::stream::*;
+use futures::future;
+use futures::stream::{self, StreamExt};
 use http::header::{
 	ACCEPT_RANGES, CONTENT_LENGTH, CONTENT_RANGE, CONTENT_TYPE, ETAG, IF_MODIFIED_SINCE,
 	IF_NONE_MATCH, LAST_MODIFIED, RANGE,
 };
 use hyper::{Body, Request, Response, StatusCode};
+use tokio::sync::mpsc;
 
 use garage_rpc::rpc_helper::{netapp::stream::ByteStream, OrderTag};
 use garage_table::EmptyKey;
 use garage_util::data::*;
+use garage_util::error::OkOrMessage;
 
 use garage_model::garage::Garage;
 use garage_model::s3::object_table::*;
@@ -242,43 +245,56 @@ pub async fn handle_get(
 			Ok(resp_builder.body(body)?)
 		}
 		ObjectVersionData::FirstBlock(_, first_block_hash) => {
-			let order_stream = OrderTag::stream();
-
-			let read_first_block = garage
-				.block_manager
-				.rpc_get_block_streaming(first_block_hash, Some(order_stream.order(0)));
-			let get_next_blocks = garage.version_table.get(&last_v.uuid, &EmptyKey);
+			let (tx, rx) = mpsc::channel(2);
 
-			let (first_block_stream, version) =
-				futures::try_join!(read_first_block, get_next_blocks)?;
-			let version = version.ok_or(Error::NoSuchKey)?;
+			let order_stream = OrderTag::stream();
+			let first_block_hash = *first_block_hash;
+			let version_uuid = last_v.uuid;
+
+			tokio::spawn(async move {
+				match async {
+					let garage2 = garage.clone();
+					let version_fut = tokio::spawn(async move {
+						garage2.version_table.get(&version_uuid, &EmptyKey).await
+					});
+
+					let stream_block_0 = garage
+						.block_manager
+						.rpc_get_block_streaming(&first_block_hash, Some(order_stream.order(0)))
+						.await?;
+					tx.send(stream_block_0)
+						.await
+						.ok_or_message("channel closed")?;
+
+					let version = version_fut.await.unwrap()?.ok_or(Error::NoSuchKey)?;
+					for (i, (_, vb)) in version.blocks.items().iter().enumerate().skip(1) {
+						let stream_block_i = garage
+							.block_manager
+							.rpc_get_block_streaming(&vb.hash, Some(order_stream.order(i as u64)))
+							.await?;
+						tx.send(stream_block_i)
+							.await
+							.ok_or_message("channel closed")?;
+					}
 
-			let mut blocks = version
-				.blocks
-				.items()
-				.iter()
-				.map(|(_, vb)| (vb.hash, None))
-				.collect::<Vec<_>>();
-			blocks[0].1 = Some(first_block_stream);
-
-			let body_stream = futures::stream::iter(blocks)
-				.enumerate()
-				.map(move |(i, (hash, stream_opt))| {
-					let garage = garage.clone();
-					async move {
-						if let Some(stream) = stream_opt {
-							stream
-						} else {
-							garage
-								.block_manager
-								.rpc_get_block_streaming(&hash, Some(order_stream.order(i as u64)))
-								.await
-								.unwrap_or_else(|e| error_stream(i, e))
-						}
+					Ok::<(), Error>(())
+				}
+				.await
+				{
+					Ok(()) => (),
+					Err(e) => {
+						let err = std::io::Error::new(
+							std::io::ErrorKind::Other,
+							format!("Error while getting object data: {}", e),
+						);
+						let _ = tx
+							.send(Box::pin(stream::once(future::ready(Err(err)))))
+							.await;
 					}
-				})
-				.buffered(2)
-				.flatten();
+				}
+			});
+
+			let body_stream = tokio_stream::wrappers::ReceiverStream::new(rx).flatten();
 
 			let body = hyper::body::Body::wrap_stream(body_stream);
 			Ok(resp_builder.body(body)?)
-- 
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