Add basic metrics to the syncer.

Cargo.lock

@@ -2592,6 +2592,7 @@ dependencies = [
  "color-eyre",
  "futures",
  "futures-util",
+ "metrics",
  "rand 0.7.3",
  "redjubjub",
  "spandoc",

zebra-consensus/Cargo.toml

@@ -15,6 +15,7 @@ tokio = { version = "0.2.22", features = ["time", "sync", "stream", "tracing"] }
 tower = "0.3"
 tracing = "0.1.16"
 tracing-futures = "0.2.4"
+metrics = "0.12"
 
 tower-batch = { path = "../tower-batch/" }
 zebra-chain = { path = "../zebra-chain" }

zebra-consensus/src/checkpoint.rs

@@ -651,6 +651,8 @@ impl Service<Arc<Block>> for CheckpointVerifier {
         // TODO(teor): retry on failure (low priority, failures should be rare)
         self.process_checkpoint_range();
 
+        metrics::gauge!("checkpoint.queued_slots", self.queued.len() as i64);
+
         async move {
             // Remove the Result<..., RecvError> wrapper from the channel future
             rx.await

zebrad/src/commands/start/sync.rs

@@ -67,13 +67,25 @@ where
     pub async fn sync(&mut self) -> Result<(), Report> {
         loop {
             self.obtain_tips().await?;
+            metrics::gauge!(
+                "sync.prospective_tips.len",
+                self.prospective_tips.len() as i64
+            );
+            metrics::gauge!("sync.pending_blocks.len", self.pending_blocks.len() as i64);
 
             // ObtainTips Step 6
             //
             // If there are any prospective tips, call ExtendTips. Continue this step until there are no more prospective tips.
             while !self.prospective_tips.is_empty() {
                 tracing::debug!("extending prospective tips");
+
                 self.extend_tips().await?;
+
+                metrics::gauge!(
+                    "sync.prospective_tips.len",
+                    self.prospective_tips.len() as i64
+                );
+                metrics::gauge!("sync.pending_blocks.len", self.pending_blocks.len() as i64);
                 tracing::debug!(
                     pending.len = self.pending_blocks.len(),
                     limit = LOOKAHEAD_LIMIT
@@ -359,6 +371,7 @@ where
                     Ok(_) => unreachable!("wrong response to block request"),
                     Err(e) => return Err(e),
                 };
+                metrics::counter!("sync.downloaded_blocks", 1);
 
                 verifier.ready_and().await?.call(block).await
             })