diff --git a/server/database.js b/server/database.js
index 3374aff9e..76d1139ee 100644
--- a/server/database.js
+++ b/server/database.js
@@ -711,6 +711,15 @@ class Database {
         }
     }
 
+    /**
+     * TODO: Migrate the old data in the heartbeat table to the new format (stat_daily, stat_hourly, stat_minutely)
+     * It should be run once while upgrading V1 to V2
+     * @returns {Promise<void>}
+     */
+    static async migrateAggregateTable() {
+
+    }
+
 }
 
 module.exports = Database;
diff --git a/server/jobs/clear-old-data.js b/server/jobs/clear-old-data.js
index 248a4d409..d74f34845 100644
--- a/server/jobs/clear-old-data.js
+++ b/server/jobs/clear-old-data.js
@@ -11,6 +11,17 @@ const DEFAULT_KEEP_PERIOD = 180;
  */
 
 const clearOldData = async () => {
+
+    /*
+    * TODO:
+    * Since we have aggregated table now, we don't need so much data in heartbeat table.
+    * But we still need to keep the important rows, because they contain the message.
+    *
+    * In the heartbeat table:
+    *    - important rows: keep according to the setting (keepDataPeriodDays) (default 180 days)
+    *    - not important rows: keep 2 days
+    */
+
     let period = await setting("keepDataPeriodDays");
 
     // Set Default Period