feat(relay): make Postgres pool size configurable, default 50

.env.example

@@ -34,6 +34,10 @@ REDIS_URL=redis://localhost:6379
 # Max connections in the relay's shared Redis pool (default 16).
 # BUZZ_REDIS_POOL_SIZE=16
 
+# Max connections in each of the relay's Postgres pools — writer and, when
+# READ_DATABASE_URL is set, reader (default 50).
+# BUZZ_DB_POOL_SIZE=50
+
 # -----------------------------------------------------------------------------
 # Typesense (search)
 # -----------------------------------------------------------------------------

crates/buzz-relay/src/config.rs

@@ -64,6 +64,14 @@ pub struct Config {
     /// pod is only 4 — small enough that rate-limit checks, presence, and
     /// pub/sub publishes queue behind each other under load.
     pub redis_pool_size: usize,
+    /// Maximum connections in the Postgres writer/reader pools. Defaults to 50.
+    ///
+    /// The `buzz-db` default of 20 was sized for a handful of pods against
+    /// `max_connections=100`. Against Aurora (~5,000 connections) that cap
+    /// is the binding constraint: a burst of concurrent handlers exhausts
+    /// the per-pod pool and requests fail on acquire timeout while the
+    /// database sits idle.
+    pub db_pool_size: u32,
     /// Public WebSocket URL of this relay, advertised in NIP-11.
     pub relay_url: String,
     /// Public WebSocket URL of the dedicated device-pairing relay, when configured.
@@ -424,6 +432,12 @@ impl Config {
             .filter(|&v| v > 0)
             .unwrap_or(16);
 
+        let db_pool_size = std::env::var("BUZZ_DB_POOL_SIZE")
+            .ok()
+            .and_then(|v| v.parse::<u32>().ok())
+            .filter(|&v| v > 0)
+            .unwrap_or(50);
+
         let relay_url =
             std::env::var("RELAY_URL").unwrap_or_else(|_| "ws://localhost:3000".to_string());
 
@@ -875,6 +889,7 @@ impl Config {
             read_database_url,
             redis_url,
             redis_pool_size,
+            db_pool_size,
             relay_url,
             pairing_relay_url,
             max_connections,
@@ -942,6 +957,7 @@ mod tests {
         assert!(!config.database_url.is_empty());
         assert!(!config.redis_url.is_empty());
         assert_eq!(config.redis_pool_size, 16);
+        assert_eq!(config.db_pool_size, 50);
         assert!(config.max_connections > 0);
         assert!(config.send_buffer_size > 0);
         assert_eq!(config.max_frame_bytes, DEFAULT_MAX_FRAME_BYTES);
@@ -1009,6 +1025,31 @@ mod tests {
         assert_eq!(junk, 16, "unparsable value must fall back to the default");
     }
 
+    #[test]
+    fn db_pool_size_env_override_and_invalid_fallback() {
+        let _guard = ENV_MUTEX.lock().unwrap();
+        let previous = std::env::var_os("BUZZ_DB_POOL_SIZE");
+
+        std::env::set_var("BUZZ_DB_POOL_SIZE", "80");
+        let overridden = Config::from_env().expect("config").db_pool_size;
+
+        std::env::set_var("BUZZ_DB_POOL_SIZE", "0");
+        let zero = Config::from_env().expect("config").db_pool_size;
+
+        std::env::set_var("BUZZ_DB_POOL_SIZE", "not-a-number");
+        let junk = Config::from_env().expect("config").db_pool_size;
+
+        if let Some(value) = previous {
+            std::env::set_var("BUZZ_DB_POOL_SIZE", value);
+        } else {
+            std::env::remove_var("BUZZ_DB_POOL_SIZE");
+        }
+
+        assert_eq!(overridden, 80);
+        assert_eq!(zero, 50, "zero must fall back to the default");
+        assert_eq!(junk, 50, "unparsable value must fall back to the default");
+    }
+
     #[test]
     fn read_database_url_unset_or_blank_is_none() {
         let _guard = ENV_MUTEX.lock().unwrap();

crates/buzz-relay/src/main.rs

@@ -146,6 +146,7 @@ async fn main() -> anyhow::Result<()> {
     let db_config = DbConfig {
         database_url: config.database_url.clone(),
         read_database_url: config.read_database_url.clone(),
+        max_connections: config.db_pool_size,
         ..DbConfig::default()
     };
     let db = Db::new(&db_config).await.map_err(|e| {