Log the state of the connection pool once per minute

src/middleware/log_connection_pool_status.rs

@@ -0,0 +1,53 @@
+//! Log the current state of the database connection pool at most once per minute
+
+use super::prelude::*;
+use crate::app::App;
+
+use conduit::Request;
+use std::sync::{
+    atomic::{AtomicUsize, Ordering},
+    Arc, Mutex,
+};
+use std::time::{Duration, Instant};
+
+#[derive(Clone)]
+pub(crate) struct LogConnectionPoolStatus {
+    app: Arc<App>,
+    last_log_time: Arc<Mutex<Instant>>,
+    in_flight_requests: Arc<AtomicUsize>,
+}
+
+impl LogConnectionPoolStatus {
+    pub(crate) fn new(app: &Arc<App>) -> Self {
+        Self {
+            app: app.clone(),
+            last_log_time: Arc::new(Mutex::new(Instant::now())),
+            in_flight_requests: Arc::new(AtomicUsize::new(0)),
+        }
+    }
+}
+
+impl Middleware for LogConnectionPoolStatus {
+    fn before(&self, _: &mut dyn Request) -> Result<(), Box<dyn Error + Send>> {
+        let mut last_log_time = self.last_log_time.lock().unwrap_or_else(|e| e.into_inner());
+        let in_flight_requests = self.in_flight_requests.fetch_add(1, Ordering::SeqCst);
+        if last_log_time.elapsed() >= Duration::from_secs(60) {
+            *last_log_time = Instant::now();
+            println!(
+                "connection_pool_status=\"{:?}\" in_flight_requests={}",
+                self.app.diesel_database.state(),
+                in_flight_requests
+            );
+        }
+        Ok(())
+    }
+
+    fn after(
+        &self,
+        _: &mut dyn Request,
+        res: Result<Response, Box<dyn Error + Send>>,
+    ) -> Result<Response, Box<dyn Error + Send>> {
+        self.in_flight_requests.fetch_sub(1, Ordering::SeqCst);
+        res
+    }
+}

src/middleware/mod.rs

@@ -9,6 +9,7 @@ pub use self::current_user::CurrentUser;
 pub use self::debug::*;
 pub use self::ember_index_rewrite::EmberIndexRewrite;
 pub use self::head::Head;
+use self::log_connection_pool_status::LogConnectionPoolStatus;
 pub use self::security_headers::SecurityHeaders;
 pub use self::static_or_continue::StaticOrContinue;
 
@@ -19,6 +20,7 @@ mod debug;
 mod ember_index_rewrite;
 mod ensure_well_formed_500;
 mod head;
+mod log_connection_pool_status;
 mod log_request;
 mod require_user_agent;
 mod security_headers;
@@ -53,6 +55,10 @@ pub fn build_middleware(app: Arc<App>, endpoints: R404) -> MiddlewareBuilder {
         m.add(DebugRequest);
     }
 
+    if env::var_os("LOG_CONNECTION_POOL_STATUS").is_some() {
+        m.add(LogConnectionPoolStatus::new(&app));
+    }
+
     m.add(ConditionalGet);
 
     m.add(Cookie::new());