Tweak trace_sort code to show the merge order (number of active input

tapes) for each merge step.  This will give us some idea of how effective
the merge distribution algorithm is.

src/backend/utils/sort/tuplesort.c

@@ -91,7 +91,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/sort/tuplesort.c,v 1.63 2006/03/07 19:06:50 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/sort/tuplesort.c,v 1.64 2006/03/08 16:59:03 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -296,6 +296,7 @@ struct Tuplesortstate
 	int		   *tp_runs;		/* # of real runs on each tape */
 	int		   *tp_dummy;		/* # of dummy runs for each tape (D[]) */
 	int		   *tp_tapenum;		/* Actual tape numbers (TAPE[]) */
+	int			activeTapes;	/* # of active input tapes in merge pass */
 
 	/*
 	 * These variables are used after completion of sorting to keep track of
@@ -943,9 +944,15 @@ tuplesort_performsort(Tuplesortstate *state)
 
 #ifdef TRACE_SORT
 	if (trace_sort)
-		elog(LOG, "performsort done%s: %s",
-			 (state->status == TSS_FINALMERGE) ? " (except final merge)" : "",
-			 pg_rusage_show(&state->ru_start));
+	{
+		if (state->status == TSS_FINALMERGE)
+			elog(LOG, "performsort done (except %d-way final merge): %s",
+				 state->activeTapes,
+				 pg_rusage_show(&state->ru_start));
+		else
+			elog(LOG, "performsort done: %s",
+				 pg_rusage_show(&state->ru_start));
+	}
 #endif
 
 	MemoryContextSwitchTo(oldcontext);
@@ -1566,7 +1573,7 @@ mergeonerun(Tuplesortstate *state)
 
 #ifdef TRACE_SORT
 	if (trace_sort)
-		elog(LOG, "finished merge step: %s",
+		elog(LOG, "finished %d-way merge step: %s", state->activeTapes,
 			 pg_rusage_show(&state->ru_start));
 #endif
 }
@@ -1614,6 +1621,7 @@ beginmerge(Tuplesortstate *state)
 			activeTapes++;
 		}
 	}
+	state->activeTapes = activeTapes;
 
 	/*
 	 * Initialize space allocation to let each active input tape have an equal