0001-Add-EXPLAIN-option-GENERIC_PLAN.v4.patch

From baf60d9480d8022866d1ed77b00c7b8506f97f70 Mon Sep 17 00:00:00 2001
From: Laurenz Albe <laurenz.albe@cybertec.at>
Date: Mon, 9 Jan 2023 17:37:40 +0100
Subject: [PATCH] Add EXPLAIN option GENERIC_PLAN

This allows EXPLAIN to generate generic plans for parameterized
statements (that have parameter placeholders like $1 in the
statement text).

Author: Laurenz Albe
Discussion: https://postgr.es/m/0a29b954b10b57f0d135fe12aa0909bd41883eb0.camel%40cybertec.at
---
 doc/src/sgml/ref/explain.sgml         | 15 +++++++++++++++
 src/backend/commands/explain.c        |  9 +++++++++
 src/backend/parser/analyze.c          | 13 +++++++++++++
 src/backend/parser/parse_coerce.c     | 15 +++++++++++++++
 src/backend/parser/parse_expr.c       | 16 ++++++++++++++++
 src/include/commands/explain.h        |  1 +
 src/include/parser/parse_node.h       |  2 ++
 src/test/regress/expected/explain.out | 14 ++++++++++++++
 src/test/regress/sql/explain.sql      |  5 +++++
 9 files changed, 90 insertions(+)

diff --git a/doc/src/sgml/ref/explain.sgml b/doc/src/sgml/ref/explain.sgml
index d4895b9d7d..221f905a59 100644
--- a/doc/src/sgml/ref/explain.sgml
+++ b/doc/src/sgml/ref/explain.sgml
@@ -40,6 +40,7 @@ EXPLAIN [ ANALYZE ] [ VERBOSE ] <replaceable class="parameter">statement</replac
     VERBOSE [ <replaceable class="parameter">boolean</replaceable> ]
     COSTS [ <replaceable class="parameter">boolean</replaceable> ]
     SETTINGS [ <replaceable class="parameter">boolean</replaceable> ]
+    GENERIC_PLAN [ <replaceable class="parameter">boolean</replaceable> ]
     BUFFERS [ <replaceable class="parameter">boolean</replaceable> ]
     WAL [ <replaceable class="parameter">boolean</replaceable> ]
     TIMING [ <replaceable class="parameter">boolean</replaceable> ]
@@ -167,6 +168,20 @@ ROLLBACK;
     </listitem>
    </varlistentry>
 
+   <varlistentry>
+    <term><literal>GENERIC_PLAN</literal></term>
+    <listitem>
+     <para>
+      Generate a generic plan for the statement (see <xref linkend="sql-prepare"/>
+      for details about generic plans).  The statement can contain parameter
+      placeholders like <literal>$1</literal> and must be a statement that can
+      use parameters.  This option cannot be used together with
+      <literal>ANALYZE</literal>, since a statement with unknown parameters
+      cannot be executed.
+     </para>
+    </listitem>
+   </varlistentry>
+
    <varlistentry>
     <term><literal>BUFFERS</literal></term>
     <listitem>
diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c
index e4621ef8d6..7ee3d24da2 100644
--- a/src/backend/commands/explain.c
+++ b/src/backend/commands/explain.c
@@ -190,6 +190,8 @@ ExplainQuery(ParseState *pstate, ExplainStmt *stmt,
 			es->wal = defGetBoolean(opt);
 		else if (strcmp(opt->defname, "settings") == 0)
 			es->settings = defGetBoolean(opt);
+		else if (strcmp(opt->defname, "generic_plan") == 0)
+			es->generic = defGetBoolean(opt);
 		else if (strcmp(opt->defname, "timing") == 0)
 		{
 			timing_set = true;
@@ -227,6 +229,13 @@ ExplainQuery(ParseState *pstate, ExplainStmt *stmt,
 					 parser_errposition(pstate, opt->location)));
 	}
 
+	/* check that GENERIC_PLAN is not used with EXPLAIN ANALYZE */
+	if (es->generic && es->analyze)
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+				 errmsg("EXPLAIN ANALYZE cannot be used with GENERIC_PLAN")));
+
+	/* check that WAL is used with EXPLAIN ANALYZE */
 	if (es->wal && !es->analyze)
 		ereport(ERROR,
 				(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
diff --git a/src/backend/parser/analyze.c b/src/backend/parser/analyze.c
index 5b90974e83..8b56eadf7e 100644
--- a/src/backend/parser/analyze.c
+++ b/src/backend/parser/analyze.c
@@ -27,6 +27,7 @@
 #include "access/sysattr.h"
 #include "catalog/pg_proc.h"
 #include "catalog/pg_type.h"
+#include "commands/defrem.h"
 #include "miscadmin.h"
 #include "nodes/makefuncs.h"
 #include "nodes/nodeFuncs.h"
@@ -2905,6 +2906,18 @@ static Query *
 transformExplainStmt(ParseState *pstate, ExplainStmt *stmt)
 {
 	Query	   *result;
+	ListCell   *lc;
+	bool		generic_plan = false;
+
+	foreach(lc, stmt->options)
+	{
+		DefElem    *opt = (DefElem *) lfirst(lc);
+
+		if (strcmp(opt->defname, "generic_plan") == 0)
+			generic_plan = defGetBoolean(opt);
+		/* don't "break", as we want the last value */
+	}
+	pstate->p_generic_explain = generic_plan;
 
 	/* transform contained query, allowing SELECT INTO */
 	stmt->query = (Node *) transformOptionalSelectInto(pstate, stmt->query);
diff --git a/src/backend/parser/parse_coerce.c b/src/backend/parser/parse_coerce.c
index 34757da0fa..b9c8dc1a25 100644
--- a/src/backend/parser/parse_coerce.c
+++ b/src/backend/parser/parse_coerce.c
@@ -369,6 +369,21 @@ coerce_type(ParseState *pstate, Node *node,
 
 		return result;
 	}
+	/*
+	 * If we are to generate a generic plan for EXPLAIN, simply let the
+	 * parameter be of the desired type.
+	 */
+	if (IsA(node, Param) &&
+		pstate != NULL && pstate->p_generic_explain)
+	{
+		Param *param = (Param *) node;
+
+		param->paramtype = targetTypeId;
+		param->paramtypmod = targetTypeMod;
+		param->location = location;
+
+		return node;
+	}
 	if (IsA(node, Param) &&
 		pstate != NULL && pstate->p_coerce_param_hook != NULL)
 	{
diff --git a/src/backend/parser/parse_expr.c b/src/backend/parser/parse_expr.c
index 53e904ca6d..26f42bcc38 100644
--- a/src/backend/parser/parse_expr.c
+++ b/src/backend/parser/parse_expr.c
@@ -808,6 +808,22 @@ transformParamRef(ParseState *pstate, ParamRef *pref)
 {
 	Node	   *result;
 
+	/* for "generic_plan" EXPLAIN, supply an unknown parameter */
+	if (pstate->p_generic_explain)
+	{
+		Param  *param;
+
+		param = makeNode(Param);
+		param->paramkind = PARAM_EXTERN;
+		param->paramid = pref->number;
+		param->paramtype = UNKNOWNOID;
+		param->paramtypmod = -1;
+		param->paramcollid = InvalidOid;
+		param->location = pref->location;
+
+		return (Node *)param;
+	}
+
 	/*
 	 * The core parser knows nothing about Params.  If a hook is supplied,
 	 * call it.  If not, or if the hook returns NULL, throw a generic error.
diff --git a/src/include/commands/explain.h b/src/include/commands/explain.h
index 7c1071ddd1..3d3e632a0c 100644
--- a/src/include/commands/explain.h
+++ b/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		generic;		/* generate a generic plan */
 	ExplainFormat format;		/* output format */
 	/* state for output formatting --- not reset for each new plan tree */
 	int			indent;			/* current indentation level */
diff --git a/src/include/parser/parse_node.h b/src/include/parser/parse_node.h
index 1a3792236a..90be0bd5ed 100644
--- a/src/include/parser/parse_node.h
+++ b/src/include/parser/parse_node.h
@@ -207,6 +207,8 @@ struct ParseState
 										 * with FOR UPDATE/FOR SHARE */
 	bool		p_resolve_unknowns; /* resolve unknown-type SELECT outputs as
 									 * type text */
+	bool		p_generic_explain;	/* accept undefined parameter
+									 * placeholders */
 
 	QueryEnvironment *p_queryEnv;	/* curr env, incl refs to enclosing env */
 
diff --git a/src/test/regress/expected/explain.out b/src/test/regress/expected/explain.out
index 48620edbc2..18f7ac93c4 100644
--- a/src/test/regress/expected/explain.out
+++ b/src/test/regress/expected/explain.out
@@ -517,3 +517,17 @@ select explain_filter('explain (verbose) select * from int8_tbl i8');
  Query Identifier: N
 (3 rows)
 
+-- Test EXPLAIN (GENERIC_PLAN)
+select explain_filter('explain (generic_plan) select unique1 from tenk1 where thousand = $1');
+                                 explain_filter                                  
+---------------------------------------------------------------------------------
+ Bitmap Heap Scan on tenk1  (cost=N.N..N.N rows=N width=N)
+   Recheck Cond: (thousand = $N)
+   ->  Bitmap Index Scan on tenk1_thous_tenthous  (cost=N.N..N.N rows=N width=N)
+         Index Cond: (thousand = $N)
+(4 rows)
+
+-- should fail
+select explain_filter('explain (analyze, generic_plan) select unique1 from tenk1 where thousand = $1');
+ERROR:  EXPLAIN ANALYZE cannot be used with GENERIC_PLAN
+CONTEXT:  PL/pgSQL function explain_filter(text) line 5 at FOR over EXECUTE statement
diff --git a/src/test/regress/sql/explain.sql b/src/test/regress/sql/explain.sql
index ae3f7a308d..fce031775a 100644
--- a/src/test/regress/sql/explain.sql
+++ b/src/test/regress/sql/explain.sql
@@ -128,3 +128,8 @@ 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 EXPLAIN (GENERIC_PLAN)
+select explain_filter('explain (generic_plan) select unique1 from tenk1 where thousand = $1');
+-- should fail
+select explain_filter('explain (analyze, generic_plan) select unique1 from tenk1 where thousand = $1');
-- 
2.39.0