backend: reduce number of concurrent db connections

backend/src/bin/worker.rs

@@ -14,7 +14,7 @@ async fn main() -> anyhow::Result<()> {
     init_tracing();
 
     let config = AppConfig::from_env()?;
-    let pool = db::init_pool(&config.database_url)?;
+    let pool = db::init_pool_with_size(&config.database_url, 1)?;
     let s3_client = build_client(&config).await?;
     let storage = Arc::new(S3Storage::new(s3_client, config.s3_bucket.clone()));
     let jwt = JwtService::from_config(&config)?;

backend/src/db.rs

@@ -5,10 +5,17 @@ use diesel::r2d2::{ConnectionManager, Pool};
 
 pub type PgPool = Pool<ConnectionManager<PgConnection>>;
 
+const DEFAULT_MAX_POOL_SIZE: u32 = 2;
+
 pub fn init_pool(database_url: &str) -> anyhow::Result<PgPool> {
+    init_pool_with_size(database_url, DEFAULT_MAX_POOL_SIZE)
+}
+
+pub fn init_pool_with_size(database_url: &str, max_size: u32) -> anyhow::Result<PgPool> {
     let manager = ConnectionManager::<PgConnection>::new(database_url);
+    let pool_size = max_size.max(1);
     let pool = Pool::builder()
-        .max_size(16)
+        .max_size(pool_size)
         .connection_timeout(Duration::from_secs(10))
         .build(manager)?;
     Ok(pool)