v2-0001-Add-shared_memory_size-GUC.patch

From e2345206dacec8b4454c3b429d0cfac01d5a0a58 Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Mon, 30 Aug 2021 16:24:59 +0900
Subject: [PATCH] Add shared_memory_size GUC

---
 src/include/storage/ipc.h           |   1 +
 src/backend/postmaster/postmaster.c |  60 +++++++-----
 src/backend/storage/ipc/ipci.c      | 142 ++++++++++++++++------------
 src/backend/utils/misc/guc.c        |  13 +++
 4 files changed, 135 insertions(+), 81 deletions(-)

diff --git a/src/include/storage/ipc.h b/src/include/storage/ipc.h
index 753a6dd4d7..80e191d407 100644
--- a/src/include/storage/ipc.h
+++ b/src/include/storage/ipc.h
@@ -77,6 +77,7 @@ extern void check_on_shmem_exit_lists_are_empty(void);
 /* ipci.c */
 extern PGDLLIMPORT shmem_startup_hook_type shmem_startup_hook;
 
+extern Size CalculateShmemSize(int *num_semaphores);
 extern void CreateSharedMemoryAndSemaphores(void);
 
 #endif							/* IPC_H */
diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index 9c2c98614a..0d3b4b1be0 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -893,6 +893,44 @@ PostmasterMain(int argc, char *argv[])
 	if (!SelectConfigFiles(userDoption, progname))
 		ExitPostmaster(2);
 
+	/* Verify that DataDir looks reasonable */
+	checkDataDir();
+
+	/* Check that pg_control exists */
+	checkControlFile();
+
+	/* And switch working directory into it */
+	ChangeToDataDir();
+
+	/*
+	 * Register the apply launcher.  Since it registers a background worker,
+	 * it needs to be called before InitializeMaxBackends(), and it's probably
+	 * a good idea to call it before any modules had chance to take the
+	 * background worker slots.
+	 */
+	ApplyLauncherRegister();
+
+	/*
+	 * Process any libraries that should be preloaded at postmaster start.
+	 * Thie happens before running -C, so as it is possible to get an
+	 * estimation of the total shared memory size allocated to this system,
+	 * accounting for the portion from loaded libraries.
+	 */
+	process_shared_preload_libraries();
+
+	/* XXX: this should be moved around */
+	{
+		char buf[64];
+		Size size;
+
+		size = CalculateShmemSize(NULL);
+		size += (1024 * 1024) - 1;
+		size /= (1024 * 1024);
+
+		sprintf(buf, "%lu MB", size);
+		SetConfigOption("shared_memory_size", buf, PGC_INTERNAL, PGC_S_OVERRIDE);
+	}
+
 	if (output_config_variable != NULL)
 	{
 		/*
@@ -907,15 +945,6 @@ PostmasterMain(int argc, char *argv[])
 		ExitPostmaster(0);
 	}
 
-	/* Verify that DataDir looks reasonable */
-	checkDataDir();
-
-	/* Check that pg_control exists */
-	checkControlFile();
-
-	/* And switch working directory into it */
-	ChangeToDataDir();
-
 	/*
 	 * Check for invalid combinations of GUC settings.
 	 */
@@ -996,19 +1025,6 @@ PostmasterMain(int argc, char *argv[])
 	 */
 	LocalProcessControlFile(false);
 
-	/*
-	 * Register the apply launcher.  Since it registers a background worker,
-	 * it needs to be called before InitializeMaxBackends(), and it's probably
-	 * a good idea to call it before any modules had chance to take the
-	 * background worker slots.
-	 */
-	ApplyLauncherRegister();
-
-	/*
-	 * process any libraries that should be preloaded at postmaster start
-	 */
-	process_shared_preload_libraries();
-
 	/*
 	 * Initialize SSL library, if specified.
 	 */
diff --git a/src/backend/storage/ipc/ipci.c b/src/backend/storage/ipc/ipci.c
index 3e4ec53a97..b225b1ee70 100644
--- a/src/backend/storage/ipc/ipci.c
+++ b/src/backend/storage/ipc/ipci.c
@@ -75,6 +75,87 @@ RequestAddinShmemSpace(Size size)
 	total_addin_request = add_size(total_addin_request, size);
 }
 
+/*
+ * CalculateShmemSize
+ *		Calculates the amount of shared memory and number of semaphores needed.
+ *
+ * If num_semaphores is not NULL, it will be set to the number of semaphores
+ * required.
+ *
+ * Note that this function freezes the additional shared memory request size
+ * from loadable modules.
+ */
+Size
+CalculateShmemSize(int *num_semaphores)
+{
+	Size size;
+	int numSemas;
+
+	/* Compute number of semaphores we'll need */
+	numSemas = ProcGlobalSemas();
+	numSemas += SpinlockSemas();
+
+	/* Return the number of semaphores if requested by the caller */
+	if (num_semaphores)
+		*num_semaphores = numSemas;
+
+	/*
+	 * Size of the Postgres shared-memory block is estimated via moderately-
+	 * accurate estimates for the big hogs, plus 100K for the stuff that's too
+	 * small to bother with estimating.
+	 *
+	 * We take some care to ensure that the total size request doesn't overflow
+	 * size_t.  If this gets through, we don't need to be so careful during the
+	 * actual allocation phase.
+	 */
+	size = 100000;
+	size = add_size(size, PGSemaphoreShmemSize(numSemas));
+	size = add_size(size, SpinlockSemaSize());
+	size = add_size(size, hash_estimate_size(SHMEM_INDEX_SIZE,
+											 sizeof(ShmemIndexEnt)));
+	size = add_size(size, dsm_estimate_size());
+	size = add_size(size, BufferShmemSize());
+	size = add_size(size, LockShmemSize());
+	size = add_size(size, PredicateLockShmemSize());
+	size = add_size(size, ProcGlobalShmemSize());
+	size = add_size(size, XLOGShmemSize());
+	size = add_size(size, CLOGShmemSize());
+	size = add_size(size, CommitTsShmemSize());
+	size = add_size(size, SUBTRANSShmemSize());
+	size = add_size(size, TwoPhaseShmemSize());
+	size = add_size(size, BackgroundWorkerShmemSize());
+	size = add_size(size, MultiXactShmemSize());
+	size = add_size(size, LWLockShmemSize());
+	size = add_size(size, ProcArrayShmemSize());
+	size = add_size(size, BackendStatusShmemSize());
+	size = add_size(size, SInvalShmemSize());
+	size = add_size(size, PMSignalShmemSize());
+	size = add_size(size, ProcSignalShmemSize());
+	size = add_size(size, CheckpointerShmemSize());
+	size = add_size(size, AutoVacuumShmemSize());
+	size = add_size(size, ReplicationSlotsShmemSize());
+	size = add_size(size, ReplicationOriginShmemSize());
+	size = add_size(size, WalSndShmemSize());
+	size = add_size(size, WalRcvShmemSize());
+	size = add_size(size, PgArchShmemSize());
+	size = add_size(size, ApplyLauncherShmemSize());
+	size = add_size(size, SnapMgrShmemSize());
+	size = add_size(size, BTreeShmemSize());
+	size = add_size(size, SyncScanShmemSize());
+	size = add_size(size, AsyncShmemSize());
+#ifdef EXEC_BACKEND
+	size = add_size(size, ShmemBackendArraySize());
+#endif
+
+	/* freeze the addin request size and include it */
+	addin_request_allowed = false;
+	size = add_size(size, total_addin_request);
+
+	/* might as well round it off to a multiple of a typical page size */
+	size = add_size(size, 8192 - (size % 8192));
+
+	return size;
+}
 
 /*
  * CreateSharedMemoryAndSemaphores
@@ -102,65 +183,8 @@ CreateSharedMemoryAndSemaphores(void)
 		Size		size;
 		int			numSemas;
 
-		/* Compute number of semaphores we'll need */
-		numSemas = ProcGlobalSemas();
-		numSemas += SpinlockSemas();
-
-		/*
-		 * Size of the Postgres shared-memory block is estimated via
-		 * moderately-accurate estimates for the big hogs, plus 100K for the
-		 * stuff that's too small to bother with estimating.
-		 *
-		 * We take some care during this phase to ensure that the total size
-		 * request doesn't overflow size_t.  If this gets through, we don't
-		 * need to be so careful during the actual allocation phase.
-		 */
-		size = 100000;
-		size = add_size(size, PGSemaphoreShmemSize(numSemas));
-		size = add_size(size, SpinlockSemaSize());
-		size = add_size(size, hash_estimate_size(SHMEM_INDEX_SIZE,
-												 sizeof(ShmemIndexEnt)));
-		size = add_size(size, dsm_estimate_size());
-		size = add_size(size, BufferShmemSize());
-		size = add_size(size, LockShmemSize());
-		size = add_size(size, PredicateLockShmemSize());
-		size = add_size(size, ProcGlobalShmemSize());
-		size = add_size(size, XLOGShmemSize());
-		size = add_size(size, CLOGShmemSize());
-		size = add_size(size, CommitTsShmemSize());
-		size = add_size(size, SUBTRANSShmemSize());
-		size = add_size(size, TwoPhaseShmemSize());
-		size = add_size(size, BackgroundWorkerShmemSize());
-		size = add_size(size, MultiXactShmemSize());
-		size = add_size(size, LWLockShmemSize());
-		size = add_size(size, ProcArrayShmemSize());
-		size = add_size(size, BackendStatusShmemSize());
-		size = add_size(size, SInvalShmemSize());
-		size = add_size(size, PMSignalShmemSize());
-		size = add_size(size, ProcSignalShmemSize());
-		size = add_size(size, CheckpointerShmemSize());
-		size = add_size(size, AutoVacuumShmemSize());
-		size = add_size(size, ReplicationSlotsShmemSize());
-		size = add_size(size, ReplicationOriginShmemSize());
-		size = add_size(size, WalSndShmemSize());
-		size = add_size(size, WalRcvShmemSize());
-		size = add_size(size, PgArchShmemSize());
-		size = add_size(size, ApplyLauncherShmemSize());
-		size = add_size(size, SnapMgrShmemSize());
-		size = add_size(size, BTreeShmemSize());
-		size = add_size(size, SyncScanShmemSize());
-		size = add_size(size, AsyncShmemSize());
-#ifdef EXEC_BACKEND
-		size = add_size(size, ShmemBackendArraySize());
-#endif
-
-		/* freeze the addin request size and include it */
-		addin_request_allowed = false;
-		size = add_size(size, total_addin_request);
-
-		/* might as well round it off to a multiple of a typical page size */
-		size = add_size(size, 8192 - (size % 8192));
-
+		/* Compute the size of the shared-memory block */
+		size = CalculateShmemSize(&numSemas);
 		elog(DEBUG3, "invoking IpcMemoryCreate(size=%zu)", size);
 
 		/*
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 467b0fd6fe..872bdc1c8e 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -620,6 +620,8 @@ char	   *pgstat_temp_directory;
 
 char	   *application_name;
 
+int			shmem_size_mb;
+
 int			tcp_keepalives_idle;
 int			tcp_keepalives_interval;
 int			tcp_keepalives_count;
@@ -2337,6 +2339,17 @@ static struct config_int ConfigureNamesInt[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"shared_memory_size", PGC_INTERNAL, RESOURCES_MEM,
+			gettext_noop("Shows the amount of shared memory allocated by the server (rounded up to the nearest MB)."),
+			NULL,
+			GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE | GUC_UNIT_MB
+		},
+		&shmem_size_mb,
+		0, 0, INT_MAX,
+		NULL, NULL, NULL
+	},
+
 	{
 		{"temp_buffers", PGC_USERSET, RESOURCES_MEM,
 			gettext_noop("Sets the maximum number of temporary buffers used by each session."),
-- 
2.33.0