Add Postgres pool settings and application name

Introduce CONFIG fields for POSTGRES_POOL_MAX_CONNECTIONS,
POSTGRES_POOL_ACQUIRE_TIMEOUT_SEC and APPLICATION_NAME.
Defaults are 10, 300s and 'users_settings_server' respectively.
Include application_name in the DB URL and apply the config
values to the PgPool options; add a log message on creation.

src/config.rs

@@ -9,6 +9,11 @@ pub struct Config {
     pub postgres_port: u32,
     pub postgres_db: String,
 
+    pub postgres_pool_max_connections: u32,
+    pub postgres_pool_acquire_timeout_sec: u64,
+
+    pub application_name: String,
+
     pub sentry_dsn: String,
 }
 
@@ -16,6 +21,10 @@ fn get_env(env: &'static str) -> String {
     std::env::var(env).unwrap_or_else(|_| panic!("Cannot get the {} env variable", env))
 }
 
+fn get_env_or(env: &'static str, default: &'static str) -> String {
+    std::env::var(env).unwrap_or_else(|_| default.to_string())
+}
+
 impl Config {
     pub fn load() -> Config {
         Config {
@@ -27,6 +36,16 @@ impl Config {
             postgres_port: get_env("POSTGRES_PORT").parse().unwrap(),
             postgres_db: get_env("POSTGRES_DB"),
 
+            postgres_pool_max_connections: std::env::var("POSTGRES_POOL_MAX_CONNECTIONS")
+                .ok()
+                .and_then(|s| s.parse().ok())
+                .unwrap_or(10),
+            postgres_pool_acquire_timeout_sec: std::env::var("POSTGRES_POOL_ACQUIRE_TIMEOUT_SEC")
+                .ok()
+                .and_then(|s| s.parse().ok())
+                .unwrap_or(300),
+            application_name: get_env_or("APPLICATION_NAME", "users_settings_server"),
+
             sentry_dsn: get_env("SENTRY_DSN"),
         }
     }

src/db.rs

@@ -5,17 +5,27 @@ use tracing::info;
 
 pub async fn get_postgres_pool() -> PgPool {
     let database_url: String = format!(
-        "postgresql://{}:{}@{}:{}/{}",
+        "postgresql://{}:{}@{}:{}/{}?application_name={}",
         CONFIG.postgres_user,
         CONFIG.postgres_password,
         CONFIG.postgres_host,
         CONFIG.postgres_port,
-        CONFIG.postgres_db
+        CONFIG.postgres_db,
+        CONFIG.application_name
+    );
+
+    info!(
+        "Creating Postgres pool (app_name={}, max_connections={}, acquire_timeout_sec={})",
+        CONFIG.application_name,
+        CONFIG.postgres_pool_max_connections,
+        CONFIG.postgres_pool_acquire_timeout_sec
     );
 
     let pool = PgPoolOptions::new()
-        .max_connections(10)
-        .acquire_timeout(std::time::Duration::from_secs(300))
+        .max_connections(CONFIG.postgres_pool_max_connections)
+        .acquire_timeout(std::time::Duration::from_secs(
+            CONFIG.postgres_pool_acquire_timeout_sec,
+        ))
         .connect(&database_url)
         .await
         .unwrap();