Small improvements to compression code

script/dev-cluster.sh

@@ -35,6 +35,9 @@ data_replication_factor = 3
 meta_replication_factor = 3
 meta_epidemic_fanout = 3
 
+enable_compression = true
+compressin_level = 10
+
 [s3_api]
 api_bind_addr = "0.0.0.0:$((3910+$count))"	# the S3 API port, HTTP without TLS. Add a reverse proxy for the TLS part.
 s3_region = "garage"				# set this to anything. S3 API calls will fail if they are not made against the region set here.

src/model/block.rs

@@ -196,12 +196,12 @@ impl BlockManager {
 
 		let mut f = fs::File::create(path.clone()).await?;
 		f.write_all(&buffer).await?;
+		drop(f);
 
 		if clean_plain {
 			path.set_extension("");
 			fs::remove_file(path).await?;
 		}
-		drop(f);
 
 		Ok(Message::Ok)
 	}
@@ -516,17 +516,25 @@ impl BlockManager {
 	/// Send block to nodes that should have it
 	pub async fn rpc_put_block(&self, hash: Hash, data: Vec<u8>) -> Result<(), Error> {
 		let garage = self.garage.load_full().unwrap();
-		let compressed = zstd_encode(&data[..], garage.config.compression_level);
+
-		let message = if compressed.is_ok() && compressed.as_ref().unwrap().len() < data.len() {
+		let compressed = if garage.config.enable_compression {
-			Message::PutBlock {
+			zstd_encode(&data[..], garage.config.compression_level).ok()
-				hash,
-				data: BlockData::Compressed(compressed.unwrap()),
-			}
 		} else {
-			Message::PutBlock {
+			None
+		};
+
+		// If compressed data is not less than 7/8 of the size of the original data, i.e. if we
+		// don't gain a significant margin by compressing, then we store the plain data instead
+		// so that we don't lose time decompressing it on reads.
+		let block_data = if compressed.is_some() && compressed.as_ref().unwrap().len() < (data.len() * 7) / 8 {
+			BlockData::Compressed(compressed.unwrap())
+		} else {
+			BlockData::Plain(data)
+		};
+
+		let message = Message::PutBlock {
 				hash,
-				data: BlockData::Plain(data),
+				data: block_data,
-			}
 		};
 		let who = self.replication.write_nodes(&hash);
 		self.rpc_client

src/util/config.rs

@@ -45,6 +45,9 @@ pub struct Config {
 	#[serde(default = "default_replication_factor")]
 	pub data_replication_factor: usize,
 
+	/// Enable Zstd compression of block data
+	pub enable_compression: bool,
+
 	/// Zstd compression level used on data blocks
 	#[serde(default)]
 	pub compression_level: i32,