Expose index DB size as Prometheus gauge metric

Fixes #541.

Cargo.lock

@@ -342,6 +342,7 @@ dependencies = [
  "dirs-next",
  "electrs-rocksdb",
  "env_logger",
+ "fs_extra",
  "log",
  "parking_lot",
  "prometheus",
@@ -423,6 +424,12 @@ dependencies = [
  "percent-encoding",
 ]
 
+[[package]]
+name = "fs_extra"
+version = "1.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2022715d62ab30faffd124d40b76f4134a550a87792276512b18d63272333394"
+
 [[package]]
 name = "fuchsia-cprng"
 version = "0.1.1"

Cargo.toml

@@ -28,6 +28,7 @@ configure_me = "0.4"
 crossbeam-channel = "0.5"
 dirs-next = "2.0"
 env_logger = "0.7"
+fs_extra = "1.2"
 log = "0.4"
 parking_lot = "0.11"
 prometheus = { version = "0.13", optional = true }

src/db.rs

@@ -269,6 +269,10 @@ impl DBStore {
         }
     }
 
+    pub(crate) fn get_size(&self) -> Result<u64> {
+        fs_extra::dir::get_size(self.db.path()).context("failed to get DB size")
+    }
+
     fn start_compactions(&self) {
         self.bulk_import.store(false, Ordering::Relaxed);
         for name in COLUMN_FAMILIES {

src/index.rs

@@ -16,6 +16,7 @@ struct Stats {
     update_duration: Histogram,
     update_size: Histogram,
     height: Gauge,
+    db_size: Gauge,
 }
 
 impl Stats {
@@ -34,6 +35,7 @@ impl Stats {
                 metrics::default_size_buckets(),
             ),
             height: metrics.gauge("index_height", "Latest indexed block height"),
+            db_size: metrics.gauge("index_db_size", "Index DB size (bytes)"),
         }
     }
 }
@@ -89,7 +91,8 @@ impl Index {
         };
 
         let stats = Stats::new(metrics);
-        stats.height.set(chain.height());
+        stats.height.set(chain.height() as f64);
+        stats.db_size.set(store.get_size()? as f64);
 
         Ok(Index {
             store,
@@ -166,6 +169,7 @@ impl Index {
     }
 
     pub(crate) fn sync(&mut self, daemon: &Daemon, exit_flag: &ExitFlag) -> Result<()> {
+        self.stats.db_size.set(self.store.get_size()? as f64);
         loop {
             let new_headers =
                 self.observe_duration("headers", || daemon.get_new_headers(&self.chain))?;
@@ -194,7 +198,7 @@ impl Index {
                     self.observe_duration("block", || {
                         index_single_block(block, height).extend(&mut batch)
                     });
-                    self.stats.height.set(height);
+                    self.stats.height.set(height as f64);
                 })?;
                 let heights: Vec<_> = heights.collect();
                 assert!(
@@ -205,6 +209,7 @@ impl Index {
                 batch.sort();
                 self.report_stats(&batch);
                 self.observe_duration("write", || self.store.write(batch));
+                self.stats.db_size.set(self.store.get_size()? as f64);
             }
             self.chain.update(new_headers);
         }

src/metrics.rs

@@ -74,8 +74,8 @@ mod metrics_impl {
     }
 
     impl Gauge {
-        pub fn set(&self, value: usize) {
-            self.gauge.set(value as f64)
+        pub fn set(&self, value: f64) {
+            self.gauge.set(value)
         }
     }
 
@@ -136,7 +136,7 @@ mod metrics_fake {
     pub struct Gauge {}
 
     impl Gauge {
-        pub fn set(&self, _value: usize) {}
+        pub fn set(&self, _value: f64) {}
     }
 
     #[derive(Clone)]