Add backfill progress logging

Signed-off-by: Nikolaos Karaolidis <nick@karaolidis.com>

src/threads/data/backfill/mod.rs

@@ -100,6 +100,10 @@ impl Jobs {
                 .and_then(|uuid| self.uuid_to_job.remove(&uuid));
         }
     }
+
+    pub fn len(&self) -> usize {
+        self.symbol_to_uuid.len()
+    }
 }
 
 pub async fn run(handler: Arc<Box<dyn Handler>>, mut receiver: mpsc::Receiver<Message>) {
@@ -208,7 +212,13 @@ async fn handle_message(
                 let fut = spawn(async move {
                     handler.queue_backfill(&job_group).await;
                     handler.backfill(job_group).await;
-                    backfill_jobs_clone.lock().await.remove_many(&symbols_clone);
+
+                    let mut backfill_jobs = backfill_jobs_clone.lock().await;
+                    backfill_jobs.remove_many(&symbols_clone);
+                    let remaining = backfill_jobs.len();
+                    drop(backfill_jobs);
+
+                    info!("{} {} backfills remaining.", remaining, log_string);
                 });
 
                 backfill_jobs.insert(symbols, fut);