From: Robert Haas <rhaas@postgresql.org>
Date: Wed, 2 Jul 2025 17:50:23 +0000 (-0400)
Subject: comments, skip storage of empty advice
X-Git-Url: http://git.postgresql.org/gitweb/static/gitweb.js?a=commitdiff_plain;h=0e3f96b703e28307cd429b3240bfa4bd2e6816e6;p=users%2Frhaas%2Fpostgres.git

comments, skip storage of empty advice
---

diff --git a/contrib/pg_plan_advice/pg_plan_advice.c b/contrib/pg_plan_advice/pg_plan_advice.c
index 08ebdc0b26..d002e9d26f 100644
--- a/contrib/pg_plan_advice/pg_plan_advice.c
+++ b/contrib/pg_plan_advice/pg_plan_advice.c
@@ -179,6 +179,9 @@ pg_plan_advice_ExecutorStart(QueryDesc *queryDesc, int eflags)
 		return standard_ExecutorStart(queryDesc, eflags);
 }
 
+/*
+ * Generate advice from a query plan and send it to the relevant collectors.
+ */
 static void
 pgpa_generate_advice(PlannedStmt *pstmt, const char *query_string)
 {
@@ -187,12 +190,17 @@ pgpa_generate_advice(PlannedStmt *pstmt, const char *query_string)
 	ListCell   *lc;
 	const char **rt_identifiers;
 
+	/* Construct unique identifiers for non-JOIN RTEs. */
 	rt_identifiers = pgpa_create_identifiers_for_planned_stmt(pstmt);
 
+	/* Initialization. */
 	memset(&context, 0, sizeof(pgpa_plan_walker_context));
 	context.pstmt = pstmt;
+
+	/* Walk the main plan tree. */
 	pgpa_plan_walker(&context, pstmt->planTree, 0, NULL, NULL);
 
+	/* Main plan tree walk won't reach subplans, so walk those. */
 	foreach(lc, pstmt->subplans)
 	{
 		Plan	   *plan = lfirst(lc);
@@ -201,7 +209,22 @@ pgpa_generate_advice(PlannedStmt *pstmt, const char *query_string)
 			pgpa_plan_walker(&context, plan, 0, NULL, NULL);
 	}
 
+	/* Put advice into string form. */
 	initStringInfo(&buf);
 	pgpa_output_advice(&buf, &context, rt_identifiers);
-	pgpa_collect_advice(pstmt->queryId, query_string, buf.data);
+
+	/*
+	 * If the advice string is non-empty, pass it to the collectors.
+	 *
+	 * A query such as SELECT 2+2 or SELECT * FROM generate_series(1,10)
+	 * will not produce any advice, since there are no query planning decisions
+	 * that can be influenced. It wouldn't exactly be wrong to record the
+	 * query together with the empty advice string, but there doesn't seem to
+	 * be much value in it, so skip it to save space.
+	 *
+	 * If this proves confusing to users, we might need to revist the behavior
+	 * here.
+	 */
+	if (buf.data[0] != '\0')
+		pgpa_collect_advice(pstmt->queryId, query_string, buf.data);
 }
diff --git a/contrib/pg_plan_advice/pgpa_collector.c b/contrib/pg_plan_advice/pgpa_collector.c
index 81735182f4..59d37a67a6 100644
--- a/contrib/pg_plan_advice/pgpa_collector.c
+++ b/contrib/pg_plan_advice/pgpa_collector.c
@@ -1,3 +1,15 @@
+/*-------------------------------------------------------------------------
+ *
+ * pgpa_collector.c
+ *	  collect advice into backend-local or shared memory
+ *
+ * Copyright (c) 2016-2025, PostgreSQL Global Development Group
+ *
+ *	  contrib/pg_plan_advice/pgpa_collector.c
+ *
+ *-------------------------------------------------------------------------
+ */
+
 #include "postgres.h"
 
 #include "pg_plan_advice.h"
@@ -15,6 +27,8 @@ PG_FUNCTION_INFO_V1(pg_get_collected_local_advice);
 #define ADVICE_CHUNK_SIZE		1024
 #define ADVICE_CHUNK_ARRAY_SIZE	64
 
+#define	PG_GET_ADVICE_COLUMNS	7
+
 typedef struct pgpa_collected_advice
 {
 	Oid			userid;			/* user OID */
@@ -52,20 +66,24 @@ static pgpa_collected_advice *pgpa_make_collected_advice(Oid userid,
 static void pgpa_store_local_advice(pgpa_collected_advice *ca);
 static void pgpa_trim_local_advice(void);
 
+/* Helper function to extract the query string from pgpa_collected_advice */
 static inline const char *
 query_string(pgpa_collected_advice *ca)
 {
 	return ca->textual_data;
 }
 
+/* Helper function to extract the advice string from pgpa_collected_advice */
 static inline const char *
 advice_string(pgpa_collected_advice *ca)
 {
 	return ca->textual_data + ca->advice_offset;
 }
 
-#define	PG_GET_ADVICE_COLUMNS	7
-
+/*
+ * Store collected query advice into the local or shared advice collector,
+ * as appropriate.
+ */
 void
 pgpa_collect_advice(uint64 queryId, const char *query_string,
 					const char *advice_string)