Optimizations for txhashset rewind (#1528)

chain/src/store.rs

@@ -140,6 +140,13 @@ impl ChainStore {
 		}
 	}
 
+	pub fn get_hash_by_height(&self, height: u64) -> Result<Hash, Error> {
+		option_to_not_found(
+			self.db.get_ser(&u64_to_key(HEADER_HEIGHT_PREFIX, height)),
+			&format!("Hash at height: {}", height),
+		)
+	}
+
 	pub fn get_header_by_height(&self, height: u64) -> Result<BlockHeader, Error> {
 		option_to_not_found(
 			self.db.get_ser(&u64_to_key(HEADER_HEIGHT_PREFIX, height)),

chain/src/txhashset.rs

@@ -1214,8 +1214,8 @@ fn input_pos_to_rewind(
 	head_header: &BlockHeader,
 	batch: &Batch,
 ) -> Result<Bitmap, Error> {
-	let mut bitmap = Bitmap::create();
 	let mut current = head_header.hash();
+	let mut height = head_header.height;
 
 	if head_header.height < block_header.height {
 		debug!(
@@ -1224,27 +1224,42 @@ fn input_pos_to_rewind(
 			head_header.height,
 			block_header.height
 		);
-		return Ok(bitmap);
+		return Ok(Bitmap::create());
 	}
 
-	//
-	// TODO - rework this loop to use Bitmap::fast_or() on a vec of bitmaps.
-	//
-	loop {
-		if current == block_header.hash() {
-			break;
+	// Batching up the block input bitmaps, and running fast_or() on every batch of 256 bitmaps.
+	// so to avoid maintaining a huge vec of bitmaps.
+	let bitmap_fast_or = |b_res, block_input_bitmaps: &mut Vec<Bitmap>| -> Option<Bitmap> {
+		if let Some(b) = b_res {
+			block_input_bitmaps.push(b);
+			if block_input_bitmaps.len() < 256 {
+				return None;
+			}
 		}
+		let bitmap = Bitmap::fast_or(&block_input_bitmaps.iter().collect::<Vec<&Bitmap>>());
+		block_input_bitmaps.clear();
+		block_input_bitmaps.push(bitmap.clone());
+		Some(bitmap)
+	};
 
+	let mut block_input_bitmaps: Vec<Bitmap> = vec![];
+	let bh = block_header.hash();
+
+	while current != bh {
 		// We cache recent block headers and block_input_bitmaps
 		// internally in our db layer (commit_index).
 		// I/O should be minimized or eliminated here for most
 		// rewind scenarios.
-		let current_header = commit_index.get_block_header(&current)?;
-		let input_bitmap_res = batch.get_block_input_bitmap(&current);
-		if let Ok(b) = input_bitmap_res {
-			bitmap.or_inplace(&b);
+		if let Ok(b_res) = batch.get_block_input_bitmap(&current) {
+			bitmap_fast_or(Some(b_res), &mut block_input_bitmaps);
 		}
-		current = current_header.previous;
+		if height == 0 {
+			break;
+		}
+		height -= 1;
+		current = commit_index.get_hash_by_height(height)?;
 	}
+
+	let bitmap = bitmap_fast_or(None, &mut block_input_bitmaps).unwrap();
 	Ok(bitmap)
 }

store/tests/test_bitmap.rs

@@ -12,9 +12,11 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+extern crate chrono;
 extern crate croaring;
 extern crate rand;
 
+use chrono::prelude::Utc;
 use croaring::Bitmap;
 use rand::Rng;
 
@@ -97,3 +99,62 @@ fn test_a_big_bitmap() {
 	let serialized_buffer = bitmap.serialize();
 	assert_eq!(serialized_buffer.len(), 230);
 }
+
+#[ignore]
+#[test]
+fn bench_fast_or() {
+	let nano_to_millis = 1.0 / 1_000_000.0;
+
+	let bitmaps_number = 256;
+	let size_of_each_bitmap = 1_000;
+
+	let init_bitmaps = || -> Vec<Bitmap> {
+		let mut rng = rand::thread_rng();
+		let mut bitmaps = vec![];
+		for _ in 0..bitmaps_number {
+			let mut bitmap = Bitmap::create();
+			for _ in 0..size_of_each_bitmap {
+				let n = rng.gen_range(0, 1_000_000);
+				bitmap.add(n);
+			}
+			bitmaps.push(bitmap);
+		}
+		bitmaps
+	};
+
+	let mut bitmaps = init_bitmaps();
+	let mut bitmap = Bitmap::create();
+	let start = Utc::now().timestamp_nanos();
+	for _ in 0..bitmaps_number {
+		bitmap.or_inplace(&bitmaps.pop().unwrap());
+	}
+	let fin = Utc::now().timestamp_nanos();
+	let dur_ms = (fin - start) as f64 * nano_to_millis;
+	println!(
+		"  or_inplace(): {:9.3?}ms. bitmap cardinality: {}",
+		dur_ms,
+		bitmap.cardinality()
+	);
+
+	let bitmaps = init_bitmaps();
+	let start = Utc::now().timestamp_nanos();
+	let bitmap = Bitmap::fast_or(&bitmaps.iter().map(|x| x).collect::<Vec<&Bitmap>>());
+	let fin = Utc::now().timestamp_nanos();
+	let dur_ms = (fin - start) as f64 * nano_to_millis;
+	println!(
+		"     fast_or(): {:9.3?}ms. bitmap cardinality: {}",
+		dur_ms,
+		bitmap.cardinality()
+	);
+
+	let bitmaps = init_bitmaps();
+	let start = Utc::now().timestamp_nanos();
+	let bitmap = Bitmap::fast_or_heap(&bitmaps.iter().map(|x| x).collect::<Vec<&Bitmap>>());
+	let fin = Utc::now().timestamp_nanos();
+	let dur_ms = (fin - start) as f64 * nano_to_millis;
+	println!(
+		"fast_or_heap(): {:9.3?}ms. bitmap cardinality: {}",
+		dur_ms,
+		bitmap.cardinality()
+	);
+}