Merge branch 'sz/increase_db_pool' into 'dev'

increased number of connections in the pool

See merge request memri/pod!395

libpod/src/database_pool.rs

@@ -155,20 +155,14 @@ where
             )
     };
 
-    let cpus = num_cpus::get() as u32;
+    let num_connections = u32::max(num_cpus::get() as u32 * 4, 8);
 
-    info!(cpus, "creating a database pool");
+    info!(num_connections, "creating a database pool");
 
     let pool =
             // Builder blocks until reaches requested number of connections
             r2d2::Pool::builder()
-                // Create a pool of connections equal to number of logic cores on the machine.
-                // Tokio creates the same amount of worker tasks, and since current database access
-                // is blocking, there is no point ot create more.
-                // Might be beneficial to increase this limit when DB queries will be offloaded
-                // to blocking threads.
-                .max_size(cpus)
-
+                .max_size(num_connections)
                 // Calls to Pool::get will wait this long for a connection to become available before returning an error.
                 .connection_timeout(Duration::from_secs(5))
                 .build(manager)?;
@@ -860,4 +854,30 @@ pub mod tests {
         ));
         assert!(Path::new(&owner_database_path(owner)).exists());
     }
+
+    #[tokio::test]
+    async fn test_number_of_connections() {
+        let owner = "test_number_of_connections";
+        let _temp_db = TempDb::new(owner);
+
+        let database_key = DatabaseKey::from(
+            "dbdbdbdbdbdbdbdbdbdbdbdbdbdbdbdbdbdbdbdbdbdbdbdbdbdbdbdbdbdbdbdb".to_string(),
+        )
+        .unwrap();
+
+        let init_db = RwLock::new(HashMap::new());
+
+        initialize_db(owner, &init_db, &database_key).await.unwrap();
+
+        let pool = get_pool(owner, &init_db, &database_key).await.unwrap();
+
+        let num_connections = u32::max(num_cpus::get() as u32 * 4, 8);
+
+        let _conns: Vec<PooledConnection> = (0..num_connections)
+            .map(|_| get_connection_from_pool(&pool, &database_key).unwrap())
+            .collect();
+
+        // Pool is empty, expect error
+        assert!(get_connection_from_pool(&pool, &database_key).is_err());
+    }
 }