Show prefetch statistic in EXPLAIN (#249)

* Show prefetch statistic in EXPLAIN

refer #2994

* Collect per-node prefetch statistics

* Show number of prefetch duplicates in explain

Author: knizhnik

src/backend/commands/explain.c

@@ -47,7 +47,6 @@ ExplainOneQuery_hook_type ExplainOneQuery_hook = NULL;
 /* Hook for plugins to get control in explain_get_index_name() */
 explain_get_index_name_hook_type explain_get_index_name_hook = NULL;
 
-
 /* OR-able flags for ExplainXMLTag() */
 #define X_OPENING 0
 #define X_CLOSING 1
@@ -121,6 +120,7 @@ static void show_eval_params(Bitmapset *bms_params, ExplainState *es);
 static const char *explain_get_index_name(Oid indexId);
 static void show_buffer_usage(ExplainState *es, const BufferUsage *usage,
 							  bool planning);
+static void show_prefetch_info(ExplainState *es, const PrefetchInfo* prefetch_info);
 static void show_wal_usage(ExplainState *es, const WalUsage *usage);
 static void ExplainIndexScanDetails(Oid indexid, ScanDirection indexorderdir,
 									ExplainState *es);
@@ -186,6 +186,8 @@ ExplainQuery(ParseState *pstate, ExplainStmt *stmt,
 			es->costs = defGetBoolean(opt);
 		else if (strcmp(opt->defname, "buffers") == 0)
 			es->buffers = defGetBoolean(opt);
+		else if (strcmp(opt->defname, "prefetch") == 0)
+			es->prefetch = defGetBoolean(opt);
 		else if (strcmp(opt->defname, "wal") == 0)
 			es->wal = defGetBoolean(opt);
 		else if (strcmp(opt->defname, "settings") == 0)
@@ -534,7 +536,7 @@ ExplainOnePlan(PlannedStmt *plannedstmt, IntoClause *into, ExplainState *es,
 	else if (es->analyze)
 		instrument_option |= INSTRUMENT_ROWS;
 
-	if (es->buffers)
+	if (es->buffers || es->prefetch)
 		instrument_option |= INSTRUMENT_BUFFERS;
 	if (es->wal)
 		instrument_option |= INSTRUMENT_WAL;
@@ -2066,6 +2068,10 @@ ExplainNode(PlanState *planstate, List *ancestors,
 	if (es->wal && planstate->instrument)
 		show_wal_usage(es, &planstate->instrument->walusage);
 
+	/* Show prefetch usage */
+	if (es->prefetch && planstate->instrument)
+		show_prefetch_info(es, &planstate->instrument->bufusage.prefetch);
+
 	/* Prepare per-worker buffer/WAL usage */
 	if (es->workers_state && (es->buffers || es->wal) && es->verbose)
 	{
@@ -3501,6 +3507,34 @@ explain_get_index_name(Oid indexId)
 	return result;
 }
 
+/*
+ * Show prefetch statistics
+ */
+static void
+show_prefetch_info(ExplainState *es, const PrefetchInfo* prefetch_info)
+{
+	if (es->format == EXPLAIN_FORMAT_TEXT)
+	{
+			ExplainIndentText(es);
+			appendStringInfo(es->str, "Prefetch: hits=%lld misses=%lld expired=%lld duplicates=%lld\n",
+							 (long long) prefetch_info->hits,
+							 (long long) prefetch_info->misses,
+							 (long long) prefetch_info->expired,
+							 (long long) prefetch_info->duplicates);
+	}
+	else
+	{
+		ExplainPropertyInteger("Prefetch Hits", NULL,
+							   prefetch_info->hits, es);
+		ExplainPropertyInteger("Prefetch Misses", NULL,
+							   prefetch_info->misses, es);
+		ExplainPropertyInteger("Prefetch Expired Requests", NULL,
+							   prefetch_info->expired, es);
+		ExplainPropertyInteger("Prefetch Duplicated Requests", NULL,
+							   prefetch_info->duplicates, es);
+	}
+}
+
 /*
  * Show buffer usage details.
  */

src/backend/executor/instrument.c

@@ -235,6 +235,10 @@ BufferUsageAdd(BufferUsage *dst, const BufferUsage *add)
 	dst->local_blks_written += add->local_blks_written;
 	dst->temp_blks_read += add->temp_blks_read;
 	dst->temp_blks_written += add->temp_blks_written;
+	dst->prefetch.hits += add->prefetch.hits;
+	dst->prefetch.misses += add->prefetch.misses;
+	dst->prefetch.expired += add->prefetch.expired;
+	dst->prefetch.duplicates += add->prefetch.duplicates;
 	INSTR_TIME_ADD(dst->blk_read_time, add->blk_read_time);
 	INSTR_TIME_ADD(dst->blk_write_time, add->blk_write_time);
 	INSTR_TIME_ADD(dst->temp_blk_read_time, add->temp_blk_read_time);
@@ -257,6 +261,10 @@ BufferUsageAccumDiff(BufferUsage *dst,
 	dst->local_blks_written += add->local_blks_written - sub->local_blks_written;
 	dst->temp_blks_read += add->temp_blks_read - sub->temp_blks_read;
 	dst->temp_blks_written += add->temp_blks_written - sub->temp_blks_written;
+	dst->prefetch.hits += add->prefetch.hits - sub->prefetch.hits;
+	dst->prefetch.misses += add->prefetch.misses - sub->prefetch.misses;
+	dst->prefetch.expired += add->prefetch.expired - sub->prefetch.expired;
+	dst->prefetch.duplicates += add->prefetch.duplicates - sub->prefetch.duplicates;
 	INSTR_TIME_ACCUM_DIFF(dst->blk_read_time,
 						  add->blk_read_time, sub->blk_read_time);
 	INSTR_TIME_ACCUM_DIFF(dst->blk_write_time,

src/include/commands/explain.h

@@ -46,6 +46,7 @@ typedef struct ExplainState
 	bool		timing;			/* print detailed node timing */
 	bool		summary;		/* print total planning and execution timing */
 	bool		settings;		/* print modified settings */
+	bool		prefetch;		/* print prefetch statistic */
 	ExplainFormat format;		/* output format */
 	/* state for output formatting --- not reset for each new plan tree */
 	int			indent;			/* current indentation level */

src/include/executor/instrument.h

@@ -15,6 +15,14 @@
 
 #include "portability/instr_time.h"
 
+/* Prefeth statistics */
+typedef struct
+{
+	int64 hits;
+	int64 misses;
+	int64 expired;
+	int64 duplicates;
+} PrefetchInfo;
 
 /*
  * BufferUsage and WalUsage counters keep being incremented infinitely,
@@ -37,6 +45,7 @@ typedef struct BufferUsage
 	instr_time	blk_write_time; /* time spent writing blocks */
 	instr_time	temp_blk_read_time; /* time spent reading temp blocks */
 	instr_time	temp_blk_write_time;	/* time spent writing temp blocks */
+	PrefetchInfo prefetch; /* prefetch statistics */ 
 } BufferUsage;
 
 /*