Add more chattiness in server shutdown.

Early returns from the buildfarm show that there's a bit of a gap in the
logging I added in 3971f648: the portion of CreateCheckPoint()
after CheckPointGuts() can take a fair amount of time.  Add a few more
log messages in that section of code.  This too shall be reverted later.

src/backend/access/transam/xlog.c

@@ -8436,6 +8436,9 @@ CreateCheckPoint(int flags)
 
 	XLogFlush(recptr);
 
+	elog(IsPostmasterEnvironment ? LOG : NOTICE,
+		 "checkpoint WAL record flushed at %s", current_time_as_str());
+
 	/*
 	 * We mustn't write any new WAL after a shutdown checkpoint, or it will be
 	 * overwritten at next startup.  No-one should even try, this just allows
@@ -8491,6 +8494,9 @@ CreateCheckPoint(int flags)
 	UpdateControlFile();
 	LWLockRelease(ControlFileLock);
 
+	elog(IsPostmasterEnvironment ? LOG : NOTICE,
+		 "pg_control updated at %s", current_time_as_str());
+
 	/* Update shared-memory copy of checkpoint XID/epoch */
 	SpinLockAcquire(&XLogCtl->info_lck);
 	XLogCtl->ckptXidEpoch = checkPoint.nextXidEpoch;
@@ -8508,6 +8514,9 @@ CreateCheckPoint(int flags)
 	 */
 	smgrpostckpt();
 
+	elog(IsPostmasterEnvironment ? LOG : NOTICE,
+		 "smgrpostckpt() done at %s", current_time_as_str());
+
 	/*
 	 * Delete old log files (those no longer needed even for previous
 	 * checkpoint or the standbys in XLOG streaming).
@@ -8523,6 +8532,9 @@ CreateCheckPoint(int flags)
 		KeepLogSeg(recptr, &_logSegNo);
 		_logSegNo--;
 		RemoveOldXlogFiles(_logSegNo, PriorRedoPtr, recptr);
+
+		elog(IsPostmasterEnvironment ? LOG : NOTICE,
+			 "RemoveOldXlogFiles() done at %s", current_time_as_str());
 	}
 
 	/*
@@ -8540,7 +8552,11 @@ CreateCheckPoint(int flags)
 	 * StartupSUBTRANS hasn't been called yet.
 	 */
 	if (!RecoveryInProgress())
+	{
 		TruncateSUBTRANS(GetOldestXmin(NULL, false));
+		elog(IsPostmasterEnvironment ? LOG : NOTICE,
+			 "TruncateSUBTRANS() done at %s", current_time_as_str());
+	}
 
 	/* Real work is done, but log and update stats before releasing lock. */
 	LogCheckpointEnd(false);

src/backend/storage/smgr/md.c

@@ -1314,6 +1314,11 @@ mdpostckpt(void)
 		if (entry->cycle_ctr == mdckpt_cycle_ctr)
 			break;
 
+		if ((list_length(pendingUnlinks) % 1024) == 0)
+			elog(IsPostmasterEnvironment ? LOG : NOTICE,
+				 "in mdpostckpt, %d unlinks remain to do at %s",
+				 list_length(pendingUnlinks), current_time_as_str());
+
 		/* Unlink the file */
 		path = relpathperm(entry->rnode, MAIN_FORKNUM);
 		if (unlink(path) < 0)