Remove unnecessary readings during maintenance

Author: AndreiEres

substrate/client/statement-store/src/lib.rs

@@ -670,21 +670,25 @@ impl Store {
 	/// Perform periodic store maintenance
 	pub fn maintain(&self) {
 		log::trace!(target: LOG_TARGET, "Started store maintenance");
-		let deleted = self.index.write().maintain(self.timestamp());
+		let (deleted, active_count, expired_count): (Vec<_>, usize, usize) = {
+			let mut index = self.index.write();
+			let deleted = index.maintain(self.timestamp());
+			(deleted, index.entries.len(), index.expired.len())
+		};
 		let deleted: Vec<_> =
 			deleted.into_iter().map(|hash| (col::EXPIRED, hash.to_vec(), None)).collect();
-		let count = deleted.len() as u64;
+		let deleted_count = deleted.len() as u64;
 		if let Err(e) = self.db.commit(deleted) {
 			log::warn!(target: LOG_TARGET, "Error writing to the statement database: {:?}", e);
 		} else {
-			self.metrics.report(|metrics| metrics.statements_pruned.inc_by(count));
+			self.metrics.report(|metrics| metrics.statements_pruned.inc_by(deleted_count));
 		}
 		log::trace!(
 			target: LOG_TARGET,
 			"Completed store maintenance. Purged: {}, Active: {}, Expired: {}",
-			count,
-			self.index.read().entries.len(),
-			self.index.read().expired.len()
+			deleted_count,
+			active_count,
+			expired_count
 		);
 	}