0001_explain_analyze_and_detoast.patch

diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c
index 8570b14f62..50859e6a1e 100644
--- a/src/backend/commands/explain.c
+++ b/src/backend/commands/explain.c
@@ -47,6 +47,8 @@ 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;
 
+/* Forward decl for detoasting analyze */
+static const DestReceiver detoastAnalyzeDR;
 
 /* OR-able flags for ExplainXMLTag() */
 #define X_OPENING 0
@@ -192,6 +194,8 @@ ExplainQuery(ParseState *pstate, ExplainStmt *stmt,
 			es->settings = defGetBoolean(opt);
 		else if (strcmp(opt->defname, "generic_plan") == 0)
 			es->generic = defGetBoolean(opt);
+		else if (strcmp(opt->defname, "detoast") == 0)
+			es->detoast = defGetBoolean(opt);
 		else if (strcmp(opt->defname, "timing") == 0)
 		{
 			timing_set = true;
@@ -244,6 +248,12 @@ ExplainQuery(ParseState *pstate, ExplainStmt *stmt,
 				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
 				 errmsg("EXPLAIN option TIMING requires ANALYZE")));
 
+	/* check that detoast is used with EXPLAIN ANALYZE */
+	if (es->detoast && !es->analyze)
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				 errmsg("EXPLAIN option DETOAST requires ANALYZE")));
+
 	/* check that GENERIC_PLAN is not used with EXPLAIN ANALYZE */
 	if (es->generic && es->analyze)
 		ereport(ERROR,
@@ -565,9 +575,13 @@ ExplainOnePlan(PlannedStmt *plannedstmt, IntoClause *into, ExplainState *es,
 	/*
 	 * Normally we discard the query's output, but if explaining CREATE TABLE
 	 * AS, we'd better use the appropriate tuple receiver.
+	 * Also if we choose to detoast during explain, we need to send the 
+	 * tuples to a receiver that performs the detoasting
 	 */
 	if (into)
 		dest = CreateIntoRelDestReceiver(into);
+	else if (es->analyze && es->detoast)
+		dest = &detoastAnalyzeDR;
 	else
 		dest = None_Receiver;
 
@@ -5052,3 +5066,98 @@ escape_yaml(StringInfo buf, const char *str)
 {
 	escape_json(buf, str);
 }
+
+
+/* ----------------
+ *		detoasting DestReceiver functions
+ * ----------------
+ */
+/* the idea is that running  EXPLAIN (ANALYZE)  sometimes gives results that 
+ * are way unrealistic, since during explain there is no detoasting of 
+ * values. That means you get no idea what your actual query time is going
+ * to be, nor what the actual overhead of detoasting is.
+ * 
+ * if you run EXPLAIN (ANAYLZE, DETOAST) then you get an impression of
+ * what is actually happening when you use postgresql as a document-database
+ * or have large values for some other reason.
+ */
+
+/* this method receives the tuples/records during explain (analyze, detoast)
+ * and detoasts them.
+ * this method is otherwise not called and its purpose is to detoast to
+ * make analyze optionally more realistic
+ */
+static bool
+detoastAnalyzeReceive(TupleTableSlot *slot, DestReceiver *self)
+{
+	MemoryContext cxt;
+	MemoryContext oldcxt;
+	int i;
+	bool shouldFree = true;
+	TupleDesc tupdesc = slot->tts_tupleDescriptor;
+	HeapTuple tuple = ExecFetchSlotHeapTuple(slot, true, &shouldFree);
+	uint16 t_infomask = tuple->t_data->t_infomask;
+	uint16 t_infomask2 = tuple->t_data->t_infomask2;
+	bits8 *t_bits = tuple->t_data->t_bits;
+
+	/* memory context for our work */
+	cxt = AllocSetContextCreate(CurrentMemoryContext, "DetoastTupleReceive",
+		ALLOCSET_DEFAULT_SIZES);
+	oldcxt = MemoryContextSwitchTo(cxt);
+
+	/* fill all of the slot's attributes, we can now use slot->tts_values */
+	slot_getallattrs(slot);
+
+	/* iterate over all attributes of the tuple and potentially detoast them */
+	for (i = 0; i < tupdesc->natts; i++)
+	{
+		Form_pg_attribute attr;
+		bool is_null;
+		char storage;
+
+		attr = TupleDescAttr(tupdesc, i);
+		storage = attr->attstorage;
+		if (i >= (t_infomask2 & HEAP_NATTS_MASK))
+			is_null = true;
+		else
+			is_null = (t_infomask & HEAP_HASNULL) && att_isnull(i, t_bits);
+		if (!is_null && (storage == 'e' || storage == 'x' || storage == 'm')) {
+			Datum datum = slot->tts_values[i];
+			/* here simple detoast the attribute's value, making
+			 * the explain (analyze) slower, but also more realistic
+			 */
+			pg_detoast_datum_packed(datum);
+		}
+	}
+	if (shouldFree)
+		pfree(tuple);
+
+	/* free our memorycontext and return to previous */
+	MemoryContextSwitchTo(oldcxt);
+	MemoryContextDelete(cxt);
+	return true;
+}
+
+static void
+detoastAnalyzeStartup(DestReceiver *self, int operation, TupleDesc typeinfo)
+{
+	/* nothing required */
+}
+
+static void
+detoastAnalyzeCleanup(DestReceiver *self)
+{
+	/* nothing required */
+}
+
+static void
+detoastAnalyzeDestroy(DestReceiver *self)
+{
+	/* nothing required */
+}
+
+
+static const DestReceiver detoastAnalyzeDR = {
+	detoastAnalyzeReceive, detoastAnalyzeStartup, detoastAnalyzeCleanup, detoastAnalyzeDestroy,
+	DestNone
+};
diff --git a/src/include/commands/explain.h b/src/include/commands/explain.h
index 3d3e632a0c..011dffb890 100644
--- a/src/include/commands/explain.h
+++ b/src/include/commands/explain.h
@@ -47,6 +47,8 @@ typedef struct ExplainState
 	bool		summary;		/* print total planning and execution timing */
 	bool		settings;		/* print modified settings */
 	bool		generic;		/* generate a generic plan */
+	bool		detoast;        /* detoast all toasted values, only applicable
+								   when "analyze" is active. */
 	ExplainFormat format;		/* output format */
 	/* state for output formatting --- not reset for each new plan tree */
 	int			indent;			/* current indentation level */
diff --git a/src/test/regress/expected/explain.out b/src/test/regress/expected/explain.out
index 1aca77491b..eef68d1eca 100644
--- a/src/test/regress/expected/explain.out
+++ b/src/test/regress/expected/explain.out
@@ -559,3 +559,23 @@ select explain_filter('explain (verbose) select * from int8_tbl i8');
  Query Identifier: N
 (3 rows)
 
+-- Test detoast is accepted as a parameter to explain
+-- seems hard to test the expected longer runtime of detoasting
+-- since one needs to setup enough data to make such a test stable
+-- also timing are filtered out by explain_filter anyway
+create table test_detoast(id bigserial, val text);
+select explain_filter('explain (analyze,detoast) select * from test_detoast');
+                                         explain_filter                                         
+------------------------------------------------------------------------------------------------
+ Seq Scan on test_detoast  (cost=N.N..N.N rows=N width=N) (actual time=N.N..N.N rows=N loops=N)
+ Planning Time: N.N ms
+ Execution Time: N.N ms
+(3 rows)
+
+drop table test_detoast;
+-- Test detoast is _not_ accepted as a parameter to explain unless analyze is specified
+create table test_detoast(id bigserial, val text);
+select explain_filter('explain (detoast) select * from test_detoast');
+ERROR:  EXPLAIN option DETOAST requires ANALYZE
+CONTEXT:  PL/pgSQL function explain_filter(text) line 5 at FOR over EXECUTE statement
+drop table test_detoast;
diff --git a/src/test/regress/sql/explain.sql b/src/test/regress/sql/explain.sql
index b6b7beab27..43047f9cce 100644
--- a/src/test/regress/sql/explain.sql
+++ b/src/test/regress/sql/explain.sql
@@ -154,3 +154,18 @@ select explain_filter('explain (verbose) select * from t1 where pg_temp.mysin(f1
 -- Test compute_query_id
 set compute_query_id = on;
 select explain_filter('explain (verbose) select * from int8_tbl i8');
+
+-- Test detoast is accepted as a parameter to explain
+-- seems hard to test the expected longer runtime of detoasting
+-- since one needs to setup enough data to make such a test stable
+-- also timing are filtered out by explain_filter anyway
+create table test_detoast(id bigserial, val text);
+select explain_filter('explain (analyze,detoast) select * from test_detoast');
+drop table test_detoast;
+
+-- Test detoast is _not_ accepted as a parameter to explain unless analyze is specified
+create table test_detoast(id bigserial, val text);
+select explain_filter('explain (detoast) select * from test_detoast');
+drop table test_detoast;
+
+