v2-0003-Convert-pg_stat_statements-to-use-the-new-interfa.patch

From f4ea30ca38e7fc5ba22e092a27341077b6f0dcc0 Mon Sep 17 00:00:00 2001
From: Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date: Tue, 24 Feb 2026 15:45:51 +0200
Subject: [PATCH v2 3/4] Convert pg_stat_statements to use the new interface

---
 .../pg_stat_statements/pg_stat_statements.c   | 135 ++++++++----------
 1 file changed, 62 insertions(+), 73 deletions(-)

diff --git a/contrib/pg_stat_statements/pg_stat_statements.c b/contrib/pg_stat_statements/pg_stat_statements.c
index 4a427533bd8..a8c7f7b2441 100644
--- a/contrib/pg_stat_statements/pg_stat_statements.c
+++ b/contrib/pg_stat_statements/pg_stat_statements.c
@@ -258,6 +258,29 @@ typedef struct pgssSharedState
 	pgssGlobalStats stats;		/* global statistics for pgss */
 } pgssSharedState;
 
+/* Links to shared memory state */
+static pgssSharedState *pgss;
+static HTAB *pgss_hash;
+
+static void pgss_shmem_init(void *arg);
+
+static ShmemStructDesc pgssSharedStateShmemDesc =
+{
+	.name = "pg_stat_statements",
+		.size = sizeof(pgssSharedState),
+		.init_fn = pgss_shmem_init,
+		.ptr = (void *) &pgss,
+};
+
+static ShmemHashDesc pgssSharedHashDesc =
+{
+	.name = "pg_stat_statements hash",
+		.init_size = 0,			/* set from 'pgss_max' */
+		.max_size = 0,			/* set from 'pgss_max' */
+		.ptr = &pgss_hash,
+};
+
+
 /*---- Local variables ----*/
 
 /* Current nesting depth of planner/ExecutorRun/ProcessUtility calls */
@@ -274,10 +297,6 @@ static ExecutorFinish_hook_type prev_ExecutorFinish = NULL;
 static ExecutorEnd_hook_type prev_ExecutorEnd = NULL;
 static ProcessUtility_hook_type prev_ProcessUtility = NULL;
 
-/* Links to shared memory state */
-static pgssSharedState *pgss = NULL;
-static HTAB *pgss_hash = NULL;
-
 /*---- GUC variables ----*/
 
 typedef enum
@@ -365,7 +384,6 @@ static void pgss_store(const char *query, int64 queryId,
 static void pg_stat_statements_internal(FunctionCallInfo fcinfo,
 										pgssVersion api_version,
 										bool showtext);
-static Size pgss_memsize(void);
 static pgssEntry *entry_alloc(pgssHashKey *key, Size query_offset, int query_len,
 							  int encoding, bool sticky);
 static void entry_dealloc(void);
@@ -390,6 +408,8 @@ static int	comp_location(const void *a, const void *b);
 void
 _PG_init(void)
 {
+	HASHCTL		info;
+
 	/*
 	 * In order to create our shared memory area, we have to be loaded via
 	 * shared_preload_libraries.  If not, fall out without hooking into any of
@@ -470,6 +490,19 @@ _PG_init(void)
 
 	MarkGUCPrefixReserved("pg_stat_statements");
 
+	/*
+	 * Register our shared memory needs, including hash table
+	 */
+	ShmemRegisterStruct(&pgssSharedStateShmemDesc);
+
+	info.keysize = sizeof(pgssHashKey);
+	info.entrysize = sizeof(pgssEntry);
+	pgssSharedHashDesc.init_size = pgss_max;
+	pgssSharedHashDesc.max_size = pgss_max;
+	ShmemRegisterHash(&pgssSharedHashDesc,
+					  &info,
+					  HASH_ELEM | HASH_BLOBS);
+
 	/*
 	 * Install hooks.
 	 */
@@ -494,8 +527,8 @@ _PG_init(void)
 }
 
 /*
- * shmem_request hook: request additional shared resources.  We'll allocate or
- * attach to the shared resources in pgss_shmem_startup().
+ * shmem_request hook: request additional shared resources.  We'll initialize
+ * other resources in pgss_shmem_startup().
  */
 static void
 pgss_shmem_request(void)
@@ -503,21 +536,31 @@ pgss_shmem_request(void)
 	if (prev_shmem_request_hook)
 		prev_shmem_request_hook();
 
-	RequestAddinShmemSpace(pgss_memsize());
 	RequestNamedLWLockTranche("pg_stat_statements", 1);
 }
 
+static void
+pgss_shmem_init(void *arg)
+{
+	pgss->lock = &(GetNamedLWLockTranche("pg_stat_statements"))->lock;
+	pgss->cur_median_usage = ASSUMED_MEDIAN_INIT;
+	pgss->mean_query_len = ASSUMED_LENGTH_INIT;
+	SpinLockInit(&pgss->mutex);
+	pgss->extent = 0;
+	pgss->n_writers = 0;
+	pgss->gc_count = 0;
+	pgss->stats.dealloc = 0;
+	pgss->stats.stats_reset = GetCurrentTimestamp();
+}
+
 /*
- * shmem_startup hook: allocate or attach to shared memory,
- * then 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.
+ * 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)
 {
-	bool		found;
-	HASHCTL		info;
 	FILE	   *file = NULL;
 	FILE	   *qfile = NULL;
 	uint32		header;
@@ -530,54 +573,14 @@ pgss_shmem_startup(void)
 	if (prev_shmem_startup_hook)
 		prev_shmem_startup_hook();
 
-	/* reset in case this is a restart within the postmaster */
-	pgss = NULL;
-	pgss_hash = NULL;
-
-	/*
-	 * Create or attach to the shared memory state, including hash table
-	 */
-	LWLockAcquire(AddinShmemInitLock, LW_EXCLUSIVE);
-
-	pgss = ShmemInitStruct("pg_stat_statements",
-						   sizeof(pgssSharedState),
-						   &found);
-
-	if (!found)
-	{
-		/* First time through ... */
-		pgss->lock = &(GetNamedLWLockTranche("pg_stat_statements"))->lock;
-		pgss->cur_median_usage = ASSUMED_MEDIAN_INIT;
-		pgss->mean_query_len = ASSUMED_LENGTH_INIT;
-		SpinLockInit(&pgss->mutex);
-		pgss->extent = 0;
-		pgss->n_writers = 0;
-		pgss->gc_count = 0;
-		pgss->stats.dealloc = 0;
-		pgss->stats.stats_reset = GetCurrentTimestamp();
-	}
-
-	info.keysize = sizeof(pgssHashKey);
-	info.entrysize = sizeof(pgssEntry);
-	pgss_hash = ShmemInitHash("pg_stat_statements hash",
-							  pgss_max, pgss_max,
-							  &info,
-							  HASH_ELEM | HASH_BLOBS);
-
-	LWLockRelease(AddinShmemInitLock);
+	if (IsUnderPostmaster)
+		return;					/* nothing to do in backends */
 
 	/*
-	 * If we're in the postmaster (or a standalone backend...), set up a shmem
-	 * exit hook to dump the statistics to disk.
+	 * Set up a shmem exit hook to dump the statistics to disk on postmaster
+	 * (or standalone backend) exit.
 	 */
-	if (!IsUnderPostmaster)
-		on_shmem_exit(pgss_shmem_shutdown, (Datum) 0);
-
-	/*
-	 * Done if some other process already completed our initialization.
-	 */
-	if (found)
-		return;
+	on_shmem_exit(pgss_shmem_shutdown, (Datum) 0);
 
 	/*
 	 * Note: we don't bother with locks here, because there should be no other
@@ -2082,20 +2085,6 @@ pg_stat_statements_info(PG_FUNCTION_ARGS)
 	PG_RETURN_DATUM(HeapTupleGetDatum(heap_form_tuple(tupdesc, values, nulls)));
 }
 
-/*
- * Estimate shared memory space needed.
- */
-static Size
-pgss_memsize(void)
-{
-	Size		size;
-
-	size = MAXALIGN(sizeof(pgssSharedState));
-	size = add_size(size, hash_estimate_size(pgss_max, sizeof(pgssEntry)));
-
-	return size;
-}
-
 /*
  * Allocate a new hashtable entry.
  * caller must hold an exclusive lock on pgss->lock
-- 
2.47.3