Report resource usage at the end of recovery

Reporting this has been rather useful in some recent recovery speedup
work.  It also seems like something that will be useful to the average DBA
too.

Author: David Rowley
Reviewed-by: Thomas Munro
Discussion: https://postgr.es/m/CAApHDvqYVORiZxq2xPvP6_ndmmsTkvr6jSYv4UTNaFa5i1kd%3DQ%40mail.gmail.com

src/backend/access/transam/xlog.c

@@ -76,6 +76,7 @@
 #include "utils/memutils.h"
 #include "utils/ps_status.h"
 #include "utils/relmapper.h"
+#include "utils/pg_rusage.h"
 #include "utils/snapmgr.h"
 #include "utils/timestamp.h"
 
@@ -7169,6 +7170,9 @@ StartupXLOG(void)
 		{
 			ErrorContextCallback errcallback;
 			TimestampTz xtime;
+			PGRUsage	ru0;
+
+			pg_rusage_init(&ru0);
 
 			InRedo = true;
 
@@ -7435,8 +7439,9 @@ StartupXLOG(void)
 			}
 
 			ereport(LOG,
-					(errmsg("redo done at %X/%X",
-							(uint32) (ReadRecPtr >> 32), (uint32) ReadRecPtr)));
+					(errmsg("redo done at %X/%X system usage: %s",
+							(uint32) (ReadRecPtr >> 32), (uint32) ReadRecPtr,
+							pg_rusage_show(&ru0))));
 			xtime = GetLatestXTime();
 			if (xtime)
 				ereport(LOG,