v6-0005-move-pgss-shmem_startup-hook-code-into-the-new-in.patch

From 5b63794f4ae24a940aef1238ba503c51b0ee393a Mon Sep 17 00:00:00 2001
From: Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date: Thu, 19 Mar 2026 11:57:02 +0200
Subject: [PATCH v6 5/6] move pgss shmem_startup hook code into the new init_fn
 callback

---
 .../pg_stat_statements/pg_stat_statements.c   | 56 +++++++++----------
 1 file changed, 26 insertions(+), 30 deletions(-)

diff --git a/contrib/pg_stat_statements/pg_stat_statements.c b/contrib/pg_stat_statements/pg_stat_statements.c
index 8df4749a43b..8c84232f4d0 100644
--- a/contrib/pg_stat_statements/pg_stat_statements.c
+++ b/contrib/pg_stat_statements/pg_stat_statements.c
@@ -292,7 +292,6 @@ static ShmemHashDesc pgssSharedHashDesc =
 static int	nesting_level = 0;
 
 /* Saved hook values */
-static shmem_startup_hook_type prev_shmem_startup_hook = NULL;
 static post_parse_analyze_hook_type prev_post_parse_analyze_hook = NULL;
 static planner_hook_type prev_planner_hook = NULL;
 static ExecutorStart_hook_type prev_ExecutorStart = NULL;
@@ -353,7 +352,6 @@ PG_FUNCTION_INFO_V1(pg_stat_statements_1_13);
 PG_FUNCTION_INFO_V1(pg_stat_statements);
 PG_FUNCTION_INFO_V1(pg_stat_statements_info);
 
-static void pgss_shmem_startup(void);
 static void pgss_shmem_shutdown(int code, Datum arg);
 static void pgss_post_parse_analyze(ParseState *pstate, Query *query,
 									JumbleState *jstate);
@@ -492,19 +490,18 @@ _PG_init(void)
 	MarkGUCPrefixReserved("pg_stat_statements");
 
 	/*
-	 * Register our shared memory needs, including hash table
+	 * Register our shared memory needs.  Register the hash table first, so
+	 * that it's already initialized when pgss_shmem_init() is called.
 	 */
-	ShmemRegisterStruct(&pgssSharedStateShmemDesc);
-
 	pgssSharedHashDesc.init_size = pgss_max;
 	pgssSharedHashDesc.max_size = pgss_max;
 	ShmemRegisterHash(&pgssSharedHashDesc);
 
+	ShmemRegisterStruct(&pgssSharedStateShmemDesc);
+
 	/*
 	 * Install hooks.
 	 */
-	prev_shmem_startup_hook = shmem_startup_hook;
-	shmem_startup_hook = pgss_shmem_startup;
 	prev_post_parse_analyze_hook = post_parse_analyze_hook;
 	post_parse_analyze_hook = pgss_post_parse_analyze;
 	prev_planner_hook = planner_hook;
@@ -521,11 +518,29 @@ _PG_init(void)
 	ProcessUtility_hook = pgss_ProcessUtility;
 }
 
+/*
+ * Initialize our shared memory data structures at postmaster startup.
+ *
+ * Load any pre-existing statistics from file.  Also create and load the
+ * query-texts file, which is expected to exist (even if empty) while the
+ * module is enabled.
+ */
 static void
 pgss_shmem_init(void *arg)
 {
 	int			tranche_id;
+	FILE	   *file = NULL;
+	FILE	   *qfile = NULL;
+	uint32		header;
+	int32		num;
+	int32		pgver;
+	int32		i;
+	int			buffer_size;
+	char	   *buffer = NULL;
 
+	/*
+	 * Initialize the shmem area with no statistics.
+	 */
 	tranche_id = LWLockNewTrancheId("pg_stat_statements");
 	LWLockInitialize(&pgss->lock.lock, tranche_id);
 	pgss->cur_median_usage = ASSUMED_MEDIAN_INIT;
@@ -536,30 +551,9 @@ pgss_shmem_init(void *arg)
 	pgss->gc_count = 0;
 	pgss->stats.dealloc = 0;
 	pgss->stats.stats_reset = GetCurrentTimestamp();
-}
-
-/*
- * shmem_startup hook: Load any pre-existing statistics from file at
- * postmaster startup.  Also create and load the query-texts file, which is
- * expected to exist (even if empty) while the module is enabled.
- */
-static void
-pgss_shmem_startup(void)
-{
-	FILE	   *file = NULL;
-	FILE	   *qfile = NULL;
-	uint32		header;
-	int32		num;
-	int32		pgver;
-	int32		i;
-	int			buffer_size;
-	char	   *buffer = NULL;
 
-	if (prev_shmem_startup_hook)
-		prev_shmem_startup_hook();
-
-	if (IsUnderPostmaster)
-		return;					/* nothing to do in backends */
+	/* The hash table must be initialized already */
+	Assert(pgss_hash != NULL);
 
 	/*
 	 * Set up a shmem exit hook to dump the statistics to disk on postmaster
@@ -568,6 +562,8 @@ pgss_shmem_startup(void)
 	on_shmem_exit(pgss_shmem_shutdown, (Datum) 0);
 
 	/*
+	 * Load any pre-existing statistics from file.
+	 *
 	 * Note: we don't bother with locks here, because there should be no other
 	 * processes running when this code is reached.
 	 */
-- 
2.47.3