Index: src/backend/postmaster/autovacuum.c
===================================================================
--- src/backend/postmaster/autovacuum.c	(HEAD)
+++ src/backend/postmaster/autovacuum.c	(DEBUG)
@@ -899,6 +899,7 @@
 			current_time = TimestampTzPlusMilliseconds(current_time,
 													   millis_increment);
 			db->adl_next_worker = current_time;
+			elog(LOG, "rebuild_database_list: db=%u, time=%f", db->adl_datid, db->adl_next_worker);
 
 			elem = DLNewElem(db);
 			/* later elements should go closer to the head of the list */
@@ -1049,11 +1050,20 @@
 				 * the current time and the current time plus naptime.
 				 */
 				if (timestamp_cmp_internal(current_time, next) > 0)
+				{
+					elog(LOG, "do_start_worker ok1 : %f > %f", current_time, next);
 					skipit = false;
+				}
 				else if (timestamp_cmp_internal(next, curr_plus_naptime) > 0)
+				{
+					elog(LOG, "do_start_worker ok2 : %f > %f", next, curr_plus_naptime);
 					skipit = false;
+				}
 				else
+				{
+					elog(LOG, "do_start_worker skip : %f, %f, %f", current_time, next, curr_plus_naptime);
 					skipit = true;
+				}
 
 				break;
 			}
@@ -1152,6 +1162,7 @@
 				 */
 				avdb->adl_next_worker =
 					TimestampTzPlusMilliseconds(now, autovacuum_naptime * 1000);
+				elog(LOG, "launch_worker: db=%u, time=%f", avdb->adl_datid, avdb->adl_next_worker);
 
 				DLMoveToFront(elem);
 				break;