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

Author: gsstark

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;
+}