update offset debugging info

lib/workers/db-worker.js

@@ -230,8 +230,10 @@ const computeIndexFromOffset = function (channelName, offset, cb) {
             var diff = new_start - start;
             Env.Log.info('WORKER_OFFSET_UPDATE', {
                 channel: channelName,
-                old_start: start,
+                start: start,
-                new_start: new_start,
+                startMB: start / 1024 / 1024,
+                update: new_start,
+                updateMB: new_start / 1024 / 1024,
                 diff: diff,
                 diffMB: diff / 1024 / 1024,
             });