From d9f3deaa518a673e4dc8df1ff6e40f47c2637e5e Mon Sep 17 00:00:00 2001
From: Tomas Vondra <tomas@vondra.me>
Date: Thu, 5 Sep 2024 16:52:26 +0200
Subject: [PATCH v20240905 3/4] separate guc to allow benchmarking

---
 src/backend/bootstrap/bootstrap.c   |  2 --
 src/backend/postmaster/postmaster.c |  5 -----
 src/backend/tcop/postgres.c         |  3 ---
 src/backend/utils/init/postinit.c   | 34 -----------------------------
 src/backend/utils/misc/guc_tables.c | 10 +++++++++
 src/include/miscadmin.h             |  1 -
 6 files changed, 10 insertions(+), 45 deletions(-)

diff --git a/src/backend/bootstrap/bootstrap.c b/src/backend/bootstrap/bootstrap.c
index ed59dfce893..7637581a184 100644
--- a/src/backend/bootstrap/bootstrap.c
+++ b/src/backend/bootstrap/bootstrap.c
@@ -309,8 +309,6 @@ BootstrapModeMain(int argc, char *argv[], bool check_only)
 
 	InitializeMaxBackends();
 
-	InitializeFastPathLocks();
-
 	CreateSharedMemoryAndSemaphores();
 
 	/*
diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index f4a16595d7f..96bc1d1cfed 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -903,11 +903,6 @@ PostmasterMain(int argc, char *argv[])
 	 */
 	InitializeMaxBackends();
 
-	/*
-	 * Also calculate the size of the fast-path lock arrays in PGPROC.
-	 */
-	InitializeFastPathLocks();
-
 	/*
 	 * Give preloaded libraries a chance to request additional shared memory.
 	 */
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index f54ae00abca..8bc6bea1135 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -4166,9 +4166,6 @@ PostgresSingleUserMain(int argc, char *argv[],
 	/* Initialize MaxBackends */
 	InitializeMaxBackends();
 
-	/* Initialize size of fast-path lock cache. */
-	InitializeFastPathLocks();
-
 	/*
 	 * Give preloaded libraries a chance to request additional shared memory.
 	 */
diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index 1faf756c8d8..3b50ce19a2c 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -557,40 +557,6 @@ InitializeMaxBackends(void)
 						   MAX_BACKENDS)));
 }
 
-/*
- * Initialize the number of fast-path lock slots in PGPROC.
- *
- * This must be called after modules have had the chance to alter GUCs in
- * shared_preload_libraries and before shared memory size is determined.
- *
- * The default max_locks_per_xact=64 means 4 groups by default.
- *
- * We allow anything between 1 and 1024 groups, with the usual power-of-2
- * logic. The 1 is the "old" value before allowing multiple groups, 1024
- * is an arbitrary limit (matching max_locks_per_xact = 16k). Values over
- * 1024 are unlikely to be beneficial - we're likely to hit other
- * bottlenecks long before that.
- */
-void
-InitializeFastPathLocks(void)
-{
-	Assert(FastPathLockGroupsPerBackend == 0);
-
-	/* we need at least one group */
-	FastPathLockGroupsPerBackend = 1;
-
-	while (FastPathLockGroupsPerBackend < FP_LOCK_GROUPS_PER_BACKEND_MAX)
-	{
-		/* stop once we exceed max_locks_per_xact */
-		if (FastPathLockGroupsPerBackend * FP_LOCK_SLOTS_PER_GROUP >= max_locks_per_xact)
-			break;
-
-		FastPathLockGroupsPerBackend *= 2;
-	}
-
-	Assert(FastPathLockGroupsPerBackend <= FP_LOCK_GROUPS_PER_BACKEND_MAX);
-}
-
 /*
  * Early initialization of a backend (either standalone or under postmaster).
  * This happens even before InitPostgres.
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 686309db58b..cef6341979f 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -2788,6 +2788,16 @@ struct config_int ConfigureNamesInt[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"fastpath_lock_groups", PGC_POSTMASTER, LOCK_MANAGEMENT,
+			gettext_noop("Sets the maximum number of locks per transaction."),
+			gettext_noop("number of groups in the fast-path lock array.")
+		},
+		&FastPathLockGroupsPerBackend,
+		1, 1, INT_MAX,
+		NULL, NULL, NULL
+	},
+
 	{
 		{"max_pred_locks_per_transaction", PGC_POSTMASTER, LOCK_MANAGEMENT,
 			gettext_noop("Sets the maximum number of predicate locks per transaction."),
diff --git a/src/include/miscadmin.h b/src/include/miscadmin.h
index e26d108a470..25348e71eb9 100644
--- a/src/include/miscadmin.h
+++ b/src/include/miscadmin.h
@@ -475,7 +475,6 @@ extern PGDLLIMPORT ProcessingMode Mode;
 #define INIT_PG_OVERRIDE_ROLE_LOGIN		0x0004
 extern void pg_split_opts(char **argv, int *argcp, const char *optstr);
 extern void InitializeMaxBackends(void);
-extern void InitializeFastPathLocks(void);
 extern void InitPostgres(const char *in_dbname, Oid dboid,
 						 const char *username, Oid useroid,
 						 bits32 flags,
-- 
2.46.0