Add metrics to blocktxids cache

examples/index.rs

@@ -17,7 +17,7 @@ fn run() -> Result<()> {
     let config = Config::from_args();
     let metrics = Metrics::new(config.monitoring_addr);
     metrics.start();
-    let cache = Arc::new(BlockTxIDsCache::new(0));
+    let cache = Arc::new(BlockTxIDsCache::new(0, &metrics));
 
     let daemon = Daemon::new(
         &config.daemon_dir,

src/bin/electrs.rs

@@ -28,7 +28,7 @@ fn run_server(config: &Config) -> Result<()> {
     let signal = Waiter::start();
     let metrics = Metrics::new(config.monitoring_addr);
     metrics.start();
-    let blocktxids_cache = Arc::new(BlockTxIDsCache::new(config.blocktxids_cache_size));
+    let blocktxids_cache = Arc::new(BlockTxIDsCache::new(config.blocktxids_cache_size, &metrics));
 
     let daemon = Daemon::new(
         &config.daemon_dir,

src/cache.rs

@@ -1,16 +1,27 @@
 use crate::errors::*;
+use crate::metrics::{Counter, MetricOpts, Metrics};
 use bitcoin_hashes::sha256d::Hash as Sha256dHash;
 use lru::LruCache;
 use std::sync::Mutex;
 
 pub struct BlockTxIDsCache {
     map: Mutex<LruCache<Sha256dHash /* blockhash */, Vec<Sha256dHash /* txid */>>>,
+    hits: Counter,
+    misses: Counter,
 }
 
 impl BlockTxIDsCache {
-    pub fn new(capacity: usize) -> BlockTxIDsCache {
+    pub fn new(capacity: usize, metrics: &Metrics) -> BlockTxIDsCache {
         BlockTxIDsCache {
             map: Mutex::new(LruCache::new(capacity)),
+            hits: metrics.counter(MetricOpts::new(
+                "electrs_blocktxids_cache_hits",
+                "# of cache hits for list of transactions in a block",
+            )),
+            misses: metrics.counter(MetricOpts::new(
+                "electrs_blocktxids_cache_misses",
+                "# of cache misses for list of transactions in a block",
+            )),
         }
     }
 
@@ -23,9 +34,11 @@ impl BlockTxIDsCache {
         F: FnOnce() -> Result<Vec<Sha256dHash>>,
     {
         if let Some(txids) = self.map.lock().unwrap().get(blockhash) {
+            self.hits.inc();
             return Ok(txids.clone());
         }
 
+        self.misses.inc();
         let txids = load_txids_func()?;
         self.map.lock().unwrap().put(*blockhash, txids.clone());
         Ok(txids)