Change balancing method to greedy (#155)

src/app/endpoint/rtc.rs

@@ -297,7 +297,7 @@ impl RequestHandler for ConnectHandler {
 
             // There are 3 cases:
             // 1. Connecting as writer for the first time. There's no recording in that case.
-            //    Select the least loaded backend that is capable to host the room's reservation.
+            //    Select the most loaded backend that is capable to host the room's reservation.
             // 2. Connecting as reader with existing recording. Choose the backend of the active
             //    recording because Janus doesn't support clustering and it must be the same server
             //    that the writer is connected to.
@@ -311,7 +311,7 @@ impl RequestHandler for ConnectHandler {
                     .execute(&conn)?
                     .ok_or("no backend found for stream")
                     .status(ResponseStatus::UNPROCESSABLE_ENTITY)?,
-                None => db::janus_backend::least_loaded(room.id(), &conn)?
+                None => db::janus_backend::most_loaded(room.id(), &conn)?
                     .ok_or("no available backends")
                     .status(ResponseStatus::SERVICE_UNAVAILABLE)?,
             };
@@ -730,8 +730,7 @@ mod test {
                         shared_helpers::insert_agent(&conn, s1a1.agent_id(), rtc1.room_id());
 
                         // The second backend has 1 stream with 2 agents but it's not started
-                        // so it doesn't make any load on the backend and should be selected
-                        // by the balancer.
+                        // so it doesn't make any load on the backend.
                         let rtc2 = shared_helpers::insert_rtc(&conn);
 
                         factory::Recording::new()
@@ -753,7 +752,7 @@ mod test {
                         // The new rtc for which we will balance the stream.
                         let rtc3 = shared_helpers::insert_rtc(&conn);
 
-                        (rtc3, backend2)
+                        (rtc3, backend1)
                     })
                     .unwrap();
 

src/db/janus_backend.rs

@@ -189,12 +189,12 @@ impl<'a> DeleteQuery<'a> {
 
 ////////////////////////////////////////////////////////////////////////////////
 
-// Returns the least loaded backend capable to host the room with its reserve considering:
+// Returns the most loaded backend capable to host the room with its reserve considering:
 // - room opening period;
 // - actual number of online agents;
 // - optional backend capacity;
 // - optional room reserve.
-const LEAST_LOADED_SQL: &str = r#"
+const MOST_LOADED_SQL: &str = r#"
     WITH
         room_load AS (
             SELECT
@@ -239,15 +239,15 @@ const LEAST_LOADED_SQL: &str = r#"
     ON 1 = 1
     WHERE r2.id = $1
     AND   COALESCE(jb.balancer_capacity, jb.capacity, 2147483647) - COALESCE(jbl.load, 0) > COALESCE(r2.reserve, 0)
-    ORDER BY COALESCE(jb.balancer_capacity, jb.capacity, 2147483647) - COALESCE(jbl.load, 0) DESC
+    ORDER BY COALESCE(jbl.load, 0) DESC
     LIMIT 1
 "#;
 
-pub(crate) fn least_loaded(room_id: Uuid, conn: &PgConnection) -> Result<Option<Object>, Error> {
+pub(crate) fn most_loaded(room_id: Uuid, conn: &PgConnection) -> Result<Option<Object>, Error> {
     use diesel::prelude::*;
     use diesel::sql_types::Uuid;
 
-    diesel::sql_query(LEAST_LOADED_SQL)
+    diesel::sql_query(MOST_LOADED_SQL)
         .bind::<Uuid, _>(room_id)
         .get_result(conn)
         .optional()