Display explain buffers measurements in memory units rather than blocks. Also...

Display explain buffers measurements in memory units rather than blocks. Also show "Total Buffer Usage" to hint that these are totals not averages per loop

src/backend/commands/explain.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994-5, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/explain.c,v 1.200 2010/02/01 15:43:35 rhaas Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/explain.c,v 1.201 2010/02/15 02:36:26 stark Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -98,6 +98,7 @@ static void ExplainJSONLineEnding(ExplainState *es);
 static void ExplainYAMLLineStarting(ExplainState *es);
 static void escape_json(StringInfo buf, const char *str);
 static void escape_yaml(StringInfo buf, const char *str);
+static double normalize_memory(double amount, char **unit, int *precision);
 
 
 /*
@@ -1081,47 +1082,63 @@ ExplainNode(Plan *plan, PlanState *planstate,
 			if (has_shared || has_local || has_temp)
 			{
 				appendStringInfoSpaces(es->str, es->indent * 2);
-				appendStringInfoString(es->str, "Buffers:");
+				appendStringInfoString(es->str, "Total Buffer Usage:");
 
 				if (has_shared)
 				{
+					char *hit_unit, *read_unit, *written_unit;
+					int   hit_prec,  read_prec,  written_prec;
+					double hit_mem      = normalize_memory((double)usage->shared_blks_hit      * BLCKSZ, &hit_unit,      &hit_prec);
+					double read_mem     = normalize_memory((double)usage->shared_blks_read     * BLCKSZ, &read_unit,     &read_prec);
+					double written_mem  = normalize_memory((double)usage->shared_blks_written  * BLCKSZ, &written_unit,  &written_prec);
+
 					appendStringInfoString(es->str, " shared");
-					if (usage->shared_blks_hit > 0)
-						appendStringInfo(es->str, " hit=%ld",
-							usage->shared_blks_hit);
+						appendStringInfo(es->str, " hit=%.*f%s", 
+										 hit_prec, hit_mem, hit_unit);
 					if (usage->shared_blks_read > 0)
-						appendStringInfo(es->str, " read=%ld",
-							usage->shared_blks_read);
+						appendStringInfo(es->str, " read=%.*f%s",
+										 read_prec, read_mem, read_unit);
 					if (usage->shared_blks_written > 0)
-						appendStringInfo(es->str, " written=%ld",
-							usage->shared_blks_written);
+						appendStringInfo(es->str, " written=%.*f%s",
+										 written_prec, written_mem, written_unit);
 					if (has_local || has_temp)
 						appendStringInfoChar(es->str, ',');
 				}
 				if (has_local)
 				{
-					appendStringInfoString(es->str, " local");
-					if (usage->local_blks_hit > 0)
-						appendStringInfo(es->str, " hit=%ld",
-							usage->local_blks_hit);
-					if (usage->local_blks_read > 0)
-						appendStringInfo(es->str, " read=%ld",
-							usage->local_blks_read);
-					if (usage->local_blks_written > 0)
-						appendStringInfo(es->str, " written=%ld",
-							usage->local_blks_written);
+					char *hit_unit, *read_unit, *written_unit;
+					int   hit_prec,  read_prec,  written_prec;
+					double hit_mem      = normalize_memory((double)usage->local_blks_hit      * BLCKSZ, &hit_unit,      &hit_prec);
+					double read_mem     = normalize_memory((double)usage->local_blks_read     * BLCKSZ, &read_unit,     &read_prec);
+					double written_mem  = normalize_memory((double)usage->local_blks_written  * BLCKSZ, &written_unit,  &written_prec);
+
+ 					appendStringInfoString(es->str, " local");
+ 					if (usage->local_blks_hit > 0)
+						appendStringInfo(es->str, " hit=%.*f%s", 
+										 hit_prec, hit_mem, hit_unit);
+ 					if (usage->local_blks_read > 0)
+						appendStringInfo(es->str, " read=%.*f%s",
+										 read_prec, read_mem, read_unit);
+ 					if (usage->local_blks_written > 0)
+						appendStringInfo(es->str, " written=%.*f%s",
+										 written_prec, written_mem, written_unit);
 					if (has_temp)
 						appendStringInfoChar(es->str, ',');
 				}
 				if (has_temp)
 				{
+					char *read_unit, *written_unit;
+					int   read_prec,  written_prec;
+					double read_mem     = normalize_memory((double)usage->temp_blks_read     * BLCKSZ, &read_unit,     &read_prec);
+					double written_mem  = normalize_memory((double)usage->temp_blks_written  * BLCKSZ, &written_unit,  &written_prec);
+
 					appendStringInfoString(es->str, " temp");
 					if (usage->temp_blks_read > 0)
-						appendStringInfo(es->str, " read=%ld",
-							usage->temp_blks_read);
-					if (usage->temp_blks_written > 0)
-						appendStringInfo(es->str, " written=%ld",
-							usage->temp_blks_written);
+						appendStringInfo(es->str, " read=%.*f%s",
+										 read_prec, read_mem, read_unit);
+ 					if (usage->temp_blks_written > 0)
+						appendStringInfo(es->str, " written=%.*f%s",
+										 written_prec, written_mem, written_unit);
 				}
 				appendStringInfoChar(es->str, '\n');
 			}
@@ -2153,3 +2170,36 @@ escape_yaml(StringInfo buf, const char *str)
 
 	appendStringInfo(buf, "%s", str);
 }
+
+/*
+ * For a quantity of bytes pick a reasonable display unit for it and
+ * return the quantity in that unit. Also return the unit name and a
+ * reasonable precision via the reference parameters.
+ */
+
+static double normalize_memory(double amount, char **unit, int *precision)
+{
+	static char *units[] = {"bytes", "kB", "MB", "GB", "TB", "PB"};
+	char **u = units, **last = units + (sizeof(units)/sizeof(*units)-1);
+
+	while (amount > 1024.0 && u < last)
+	{
+		amount /= 1024.0;
+		u += 1;
+	}
+
+	*unit = *u;
+
+	/* if it's bytes or kB then don't print decimals since that's less
+	 * than blocksize, otherwise always print 3 significant digits */
+	if (u == units || u == units+1 )
+		*precision = 0;
+	else if (amount < 10)
+		*precision = 2;
+	else if (amount < 100)
+		*precision = 1;
+	else
+		*precision = 0;
+
+	return amount;
+}