Speed up plpgsql trigger startup by introducing "promises".

Over the years we've accreted quite a few special variables that are
predefined in plpgsql trigger functions.  The cost of initializing these
variables to their defined values turns out to be a significant part of
the runtime of simple triggers; but, undoubtedly, most real-world triggers
never examine the values of most of these variables.

To improve matters, invent the notion of a variable that has a "promise"
attached to it, specifying which of the predetermined values should be
assigned to the variable if anything ever reads it.  This eliminates all
the unneeded startup overhead, in return for a small penalty on accesses
to these variables.

Tom Lane, reviewed by Pavel Stehule

Discussion: https://postgr.es/m/11986.1514407114@sss.pgh.pa.us

src/pl/plpgsql/src/pl_comp.c

@@ -607,7 +607,9 @@ do_compile(FunctionCallInfo fcinfo,
 																-1,
 																InvalidOid),
 										 true);
-			function->tg_name_varno = var->dno;
+			Assert(var->dtype == PLPGSQL_DTYPE_VAR);
+			var->dtype = PLPGSQL_DTYPE_PROMISE;
+			((PLpgSQL_var *) var)->promise = PLPGSQL_PROMISE_TG_NAME;
 
 			/* Add the variable tg_when */
 			var = plpgsql_build_variable("tg_when", 0,
@@ -615,7 +617,9 @@ do_compile(FunctionCallInfo fcinfo,
 																-1,
 																function->fn_input_collation),
 										 true);
-			function->tg_when_varno = var->dno;
+			Assert(var->dtype == PLPGSQL_DTYPE_VAR);
+			var->dtype = PLPGSQL_DTYPE_PROMISE;
+			((PLpgSQL_var *) var)->promise = PLPGSQL_PROMISE_TG_WHEN;
 
 			/* Add the variable tg_level */
 			var = plpgsql_build_variable("tg_level", 0,
@@ -623,7 +627,9 @@ do_compile(FunctionCallInfo fcinfo,
 																-1,
 																function->fn_input_collation),
 										 true);
-			function->tg_level_varno = var->dno;
+			Assert(var->dtype == PLPGSQL_DTYPE_VAR);
+			var->dtype = PLPGSQL_DTYPE_PROMISE;
+			((PLpgSQL_var *) var)->promise = PLPGSQL_PROMISE_TG_LEVEL;
 
 			/* Add the variable tg_op */
 			var = plpgsql_build_variable("tg_op", 0,
@@ -631,7 +637,9 @@ do_compile(FunctionCallInfo fcinfo,
 																-1,
 																function->fn_input_collation),
 										 true);
-			function->tg_op_varno = var->dno;
+			Assert(var->dtype == PLPGSQL_DTYPE_VAR);
+			var->dtype = PLPGSQL_DTYPE_PROMISE;
+			((PLpgSQL_var *) var)->promise = PLPGSQL_PROMISE_TG_OP;
 
 			/* Add the variable tg_relid */
 			var = plpgsql_build_variable("tg_relid", 0,
@@ -639,7 +647,9 @@ do_compile(FunctionCallInfo fcinfo,
 																-1,
 																InvalidOid),
 										 true);
-			function->tg_relid_varno = var->dno;
+			Assert(var->dtype == PLPGSQL_DTYPE_VAR);
+			var->dtype = PLPGSQL_DTYPE_PROMISE;
+			((PLpgSQL_var *) var)->promise = PLPGSQL_PROMISE_TG_RELID;
 
 			/* Add the variable tg_relname */
 			var = plpgsql_build_variable("tg_relname", 0,
@@ -647,7 +657,9 @@ do_compile(FunctionCallInfo fcinfo,
 																-1,
 																InvalidOid),
 										 true);
-			function->tg_relname_varno = var->dno;
+			Assert(var->dtype == PLPGSQL_DTYPE_VAR);
+			var->dtype = PLPGSQL_DTYPE_PROMISE;
+			((PLpgSQL_var *) var)->promise = PLPGSQL_PROMISE_TG_TABLE_NAME;
 
 			/* tg_table_name is now preferred to tg_relname */
 			var = plpgsql_build_variable("tg_table_name", 0,
@@ -655,7 +667,9 @@ do_compile(FunctionCallInfo fcinfo,
 																-1,
 																InvalidOid),
 										 true);
-			function->tg_table_name_varno = var->dno;
+			Assert(var->dtype == PLPGSQL_DTYPE_VAR);
+			var->dtype = PLPGSQL_DTYPE_PROMISE;
+			((PLpgSQL_var *) var)->promise = PLPGSQL_PROMISE_TG_TABLE_NAME;
 
 			/* add the variable tg_table_schema */
 			var = plpgsql_build_variable("tg_table_schema", 0,
@@ -663,7 +677,9 @@ do_compile(FunctionCallInfo fcinfo,
 																-1,
 																InvalidOid),
 										 true);
-			function->tg_table_schema_varno = var->dno;
+			Assert(var->dtype == PLPGSQL_DTYPE_VAR);
+			var->dtype = PLPGSQL_DTYPE_PROMISE;
+			((PLpgSQL_var *) var)->promise = PLPGSQL_PROMISE_TG_TABLE_SCHEMA;
 
 			/* Add the variable tg_nargs */
 			var = plpgsql_build_variable("tg_nargs", 0,
@@ -671,7 +687,9 @@ do_compile(FunctionCallInfo fcinfo,
 																-1,
 																InvalidOid),
 										 true);
-			function->tg_nargs_varno = var->dno;
+			Assert(var->dtype == PLPGSQL_DTYPE_VAR);
+			var->dtype = PLPGSQL_DTYPE_PROMISE;
+			((PLpgSQL_var *) var)->promise = PLPGSQL_PROMISE_TG_NARGS;
 
 			/* Add the variable tg_argv */
 			var = plpgsql_build_variable("tg_argv", 0,
@@ -679,7 +697,9 @@ do_compile(FunctionCallInfo fcinfo,
 																-1,
 																function->fn_input_collation),
 										 true);
-			function->tg_argv_varno = var->dno;
+			Assert(var->dtype == PLPGSQL_DTYPE_VAR);
+			var->dtype = PLPGSQL_DTYPE_PROMISE;
+			((PLpgSQL_var *) var)->promise = PLPGSQL_PROMISE_TG_ARGV;
 
 			break;
 
@@ -701,7 +721,9 @@ do_compile(FunctionCallInfo fcinfo,
 																-1,
 																function->fn_input_collation),
 										 true);
-			function->tg_event_varno = var->dno;
+			Assert(var->dtype == PLPGSQL_DTYPE_VAR);
+			var->dtype = PLPGSQL_DTYPE_PROMISE;
+			((PLpgSQL_var *) var)->promise = PLPGSQL_PROMISE_TG_EVENT;
 
 			/* Add the variable tg_tag */
 			var = plpgsql_build_variable("tg_tag", 0,
@@ -709,7 +731,9 @@ do_compile(FunctionCallInfo fcinfo,
 																-1,
 																function->fn_input_collation),
 										 true);
-			function->tg_tag_varno = var->dno;
+			Assert(var->dtype == PLPGSQL_DTYPE_VAR);
+			var->dtype = PLPGSQL_DTYPE_PROMISE;
+			((PLpgSQL_var *) var)->promise = PLPGSQL_PROMISE_TG_TAG;
 
 			break;
 
@@ -1878,6 +1902,7 @@ build_row_from_vars(PLpgSQL_variable **vars, int numvars)
 		switch (var->dtype)
 		{
 			case PLPGSQL_DTYPE_VAR:
+			case PLPGSQL_DTYPE_PROMISE:
 				typoid = ((PLpgSQL_var *) var)->datatype->typoid;
 				typmod = ((PLpgSQL_var *) var)->datatype->atttypmod;
 				typcoll = ((PLpgSQL_var *) var)->datatype->collation;
@@ -2196,6 +2221,7 @@ plpgsql_finish_datums(PLpgSQL_function *function)
 		switch (function->datums[i]->dtype)
 		{
 			case PLPGSQL_DTYPE_VAR:
+			case PLPGSQL_DTYPE_PROMISE:
 				copiable_size += MAXALIGN(sizeof(PLpgSQL_var));
 				break;
 			case PLPGSQL_DTYPE_REC:

src/pl/plpgsql/src/pl_funcs.c

@@ -729,6 +729,7 @@ plpgsql_free_function_memory(PLpgSQL_function *func)
 		switch (d->dtype)
 		{
 			case PLPGSQL_DTYPE_VAR:
+			case PLPGSQL_DTYPE_PROMISE:
 				{
 					PLpgSQL_var *var = (PLpgSQL_var *) d;
 
@@ -1582,6 +1583,7 @@ plpgsql_dumptree(PLpgSQL_function *func)
 		switch (d->dtype)
 		{
 			case PLPGSQL_DTYPE_VAR:
+			case PLPGSQL_DTYPE_PROMISE:
 				{
 					PLpgSQL_var *var = (PLpgSQL_var *) d;
 
@@ -1608,6 +1610,9 @@ plpgsql_dumptree(PLpgSQL_function *func)
 						dump_expr(var->cursor_explicit_expr);
 						printf("\n");
 					}
+					if (var->promise != PLPGSQL_PROMISE_NONE)
+						printf("                                  PROMISE %d\n",
+							   (int) var->promise);
 				}
 				break;
 			case PLPGSQL_DTYPE_ROW:

src/pl/plpgsql/src/pl_gram.y

@@ -3170,6 +3170,7 @@ make_return_stmt(int location)
 
 		if (tok == T_DATUM && plpgsql_peek() == ';' &&
 			(yylval.wdatum.datum->dtype == PLPGSQL_DTYPE_VAR ||
+			 yylval.wdatum.datum->dtype == PLPGSQL_DTYPE_PROMISE ||
 			 yylval.wdatum.datum->dtype == PLPGSQL_DTYPE_ROW ||
 			 yylval.wdatum.datum->dtype == PLPGSQL_DTYPE_REC))
 		{
@@ -3231,6 +3232,7 @@ make_return_next_stmt(int location)
 
 		if (tok == T_DATUM && plpgsql_peek() == ';' &&
 			(yylval.wdatum.datum->dtype == PLPGSQL_DTYPE_VAR ||
+			 yylval.wdatum.datum->dtype == PLPGSQL_DTYPE_PROMISE ||
 			 yylval.wdatum.datum->dtype == PLPGSQL_DTYPE_ROW ||
 			 yylval.wdatum.datum->dtype == PLPGSQL_DTYPE_REC))
 		{
@@ -3318,6 +3320,7 @@ check_assignable(PLpgSQL_datum *datum, int location)
 	switch (datum->dtype)
 	{
 		case PLPGSQL_DTYPE_VAR:
+		case PLPGSQL_DTYPE_PROMISE:
 			if (((PLpgSQL_var *) datum)->isconst)
 				ereport(ERROR,
 						(errcode(ERRCODE_ERROR_IN_ASSIGNMENT),

src/pl/plpgsql/src/plpgsql.h

@@ -63,9 +63,29 @@ typedef enum PLpgSQL_datum_type
 	PLPGSQL_DTYPE_ROW,
 	PLPGSQL_DTYPE_REC,
 	PLPGSQL_DTYPE_RECFIELD,
-	PLPGSQL_DTYPE_ARRAYELEM
+	PLPGSQL_DTYPE_ARRAYELEM,
+	PLPGSQL_DTYPE_PROMISE
 } PLpgSQL_datum_type;
 
+/*
+ * DTYPE_PROMISE datums have these possible ways of computing the promise
+ */
+typedef enum PLpgSQL_promise_type
+{
+	PLPGSQL_PROMISE_NONE = 0,	/* not a promise, or promise satisfied */
+	PLPGSQL_PROMISE_TG_NAME,
+	PLPGSQL_PROMISE_TG_WHEN,
+	PLPGSQL_PROMISE_TG_LEVEL,
+	PLPGSQL_PROMISE_TG_OP,
+	PLPGSQL_PROMISE_TG_RELID,
+	PLPGSQL_PROMISE_TG_TABLE_NAME,
+	PLPGSQL_PROMISE_TG_TABLE_SCHEMA,
+	PLPGSQL_PROMISE_TG_NARGS,
+	PLPGSQL_PROMISE_TG_ARGV,
+	PLPGSQL_PROMISE_TG_EVENT,
+	PLPGSQL_PROMISE_TG_TAG
+} PLpgSQL_promise_type;
+
 /*
  * Variants distinguished in PLpgSQL_type structs
  */
@@ -248,6 +268,14 @@ typedef struct PLpgSQL_variable
 
 /*
  * Scalar variable
+ *
+ * DTYPE_VAR and DTYPE_PROMISE datums both use this struct type.
+ * A PROMISE datum works exactly like a VAR datum for most purposes,
+ * but if it is read without having previously been assigned to, then
+ * a special "promised" value is computed and assigned to the datum
+ * before the read is performed.  This technique avoids the overhead of
+ * computing the variable's value in cases where we expect that many
+ * functions will never read it.
  */
 typedef struct PLpgSQL_var
 {
@@ -271,9 +299,18 @@ typedef struct PLpgSQL_var
 	int			cursor_explicit_argrow;
 	int			cursor_options;
 
+	/* Fields below here can change at runtime */
+
 	Datum		value;
 	bool		isnull;
 	bool		freeval;
+
+	/*
+	 * The promise field records which "promised" value to assign if the
+	 * promise must be honored.  If it's a normal variable, or the promise has
+	 * been fulfilled, this is PLPGSQL_PROMISE_NONE.
+	 */
+	PLpgSQL_promise_type promise;
 } PLpgSQL_var;
 
 /*
@@ -869,20 +906,6 @@ typedef struct PLpgSQL_function
 	int			found_varno;
 	int			new_varno;
 	int			old_varno;
-	int			tg_name_varno;
-	int			tg_when_varno;
-	int			tg_level_varno;
-	int			tg_op_varno;
-	int			tg_relid_varno;
-	int			tg_relname_varno;
-	int			tg_table_name_varno;
-	int			tg_table_schema_varno;
-	int			tg_nargs_varno;
-	int			tg_argv_varno;
-
-	/* for event triggers */
-	int			tg_event_varno;
-	int			tg_tag_varno;
 
 	PLpgSQL_resolve_option resolve_option;
 
@@ -912,6 +935,9 @@ typedef struct PLpgSQL_execstate
 {
 	PLpgSQL_function *func;		/* function being executed */
 
+	TriggerData *trigdata;		/* if regular trigger, data about firing */
+	EventTriggerData *evtrigdata;	/* if event trigger, data about firing */
+
 	Datum		retval;
 	bool		retisnull;
 	Oid			rettype;		/* type of current retval */