Remove dynamic_shared_memory_type=none

PostgreSQL nowadays offers some kind of dynamic shared memory feature on
all supported platforms.  Having the choice of "none" prevents us from
relying on DSM in core features.  So this patch removes the choice of
"none".

Author: Kyotaro Horiguchi <horiguchi.kyotaro@lab.ntt.co.jp>

doc/src/sgml/config.sgml

@@ -1662,9 +1662,9 @@ include_dir 'conf.d'
         should use.  Possible values are <literal>posix</literal> (for POSIX shared
         memory allocated using <literal>shm_open</literal>), <literal>sysv</literal>
         (for System V shared memory allocated via <literal>shmget</literal>),
-        <literal>windows</literal> (for Windows shared memory), <literal>mmap</literal>
-        (to simulate shared memory using memory-mapped files stored in the
-        data directory), and <literal>none</literal> (to disable this feature).
+        <literal>windows</literal> (for Windows shared memory),
+        and <literal>mmap</literal> (to simulate shared memory using
+        memory-mapped files stored in the data directory).
         Not all values are supported on all platforms; the first supported
         option is the default for that platform.  The use of the
         <literal>mmap</literal> option, which is not the default on any platform,

doc/src/sgml/parallel.sgml

@@ -124,14 +124,6 @@ EXPLAIN SELECT * FROM pgbench_accounts WHERE filler LIKE '%x%';
         configured via <varname>max_parallel_workers_per_gather</varname>.
       </para>
     </listitem>
-
-    <listitem>
-      <para>
-        <xref linkend="guc-dynamic-shared-memory-type"/> must be set to a
-        value other than <literal>none</literal>.  Parallel query requires dynamic
-        shared memory in order to pass data between cooperating processes.
-      </para>
-    </listitem>
   </itemizedlist>
 
   <para>

src/backend/access/transam/parallel.c

@@ -161,13 +161,6 @@ CreateParallelContext(const char *library_name, const char *function_name,
 	/* Number of workers should be non-negative. */
 	Assert(nworkers >= 0);
 
-	/*
-	 * If dynamic shared memory is not available, we won't be able to use
-	 * background workers.
-	 */
-	if (dynamic_shared_memory_type == DSM_IMPL_NONE)
-		nworkers = 0;
-
 	/*
 	 * If we are running under serializable isolation, we can't use parallel
 	 * workers, at least not until somebody enhances that mechanism to be

src/backend/optimizer/plan/planner.c

@@ -335,7 +335,6 @@ standard_planner(Query *parse, int cursorOptions, ParamListInfo boundParams)
 	 */
 	if ((cursorOptions & CURSOR_OPT_PARALLEL_OK) != 0 &&
 		IsUnderPostmaster &&
-		dynamic_shared_memory_type != DSM_IMPL_NONE &&
 		parse->commandType == CMD_SELECT &&
 		!parse->hasModifyingCTE &&
 		max_parallel_workers_per_gather > 0 &&
@@ -6050,8 +6049,7 @@ plan_create_index_workers(Oid tableOid, Oid indexOid)
 	double		allvisfrac;
 
 	/* Return immediately when parallelism disabled */
-	if (dynamic_shared_memory_type == DSM_IMPL_NONE ||
-		max_parallel_maintenance_workers == 0)
+	if (max_parallel_maintenance_workers == 0)
 		return 0;
 
 	/* Set up largely-dummy planner state */

src/backend/storage/ipc/dsm.c

@@ -150,10 +150,6 @@ dsm_postmaster_startup(PGShmemHeader *shim)
 
 	Assert(!IsUnderPostmaster);
 
-	/* If dynamic shared memory is disabled, there's nothing to do. */
-	if (dynamic_shared_memory_type == DSM_IMPL_NONE)
-		return;
-
 	/*
 	 * If we're using the mmap implementations, clean up any leftovers.
 	 * Cleanup isn't needed on Windows, and happens earlier in startup for
@@ -219,10 +215,6 @@ dsm_cleanup_using_control_segment(dsm_handle old_control_handle)
 	uint32		i;
 	dsm_control_header *old_control;
 
-	/* If dynamic shared memory is disabled, there's nothing to do. */
-	if (dynamic_shared_memory_type == DSM_IMPL_NONE)
-		return;
-
 	/*
 	 * Try to attach the segment.  If this fails, it probably just means that
 	 * the operating system has been rebooted and the segment no longer
@@ -391,13 +383,6 @@ dsm_postmaster_shutdown(int code, Datum arg)
 static void
 dsm_backend_startup(void)
 {
-	/* If dynamic shared memory is disabled, reject this. */
-	if (dynamic_shared_memory_type == DSM_IMPL_NONE)
-		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("dynamic shared memory is disabled"),
-				 errhint("Set dynamic_shared_memory_type to a value other than \"none\".")));
-
 #ifdef EXEC_BACKEND
 	{
 		void	   *control_address = NULL;

src/backend/storage/ipc/dsm_impl.c

@@ -106,7 +106,6 @@ const struct config_enum_entry dynamic_shared_memory_options[] = {
 #ifdef USE_DSM_MMAP
 	{"mmap", DSM_IMPL_MMAP, false},
 #endif
-	{"none", DSM_IMPL_NONE, false},
 	{NULL, 0, false}
 };
 
@@ -210,8 +209,6 @@ dsm_impl_can_resize(void)
 {
 	switch (dynamic_shared_memory_type)
 	{
-		case DSM_IMPL_NONE:
-			return false;
 		case DSM_IMPL_POSIX:
 			return true;
 		case DSM_IMPL_SYSV:

src/backend/utils/misc/postgresql.conf.sample

@@ -133,7 +133,6 @@
 					#   sysv
 					#   windows
 					#   mmap
-					# use none to disable dynamic shared memory
 					# (change requires restart)
 
 # - Disk -

src/bin/initdb/initdb.c

@@ -984,6 +984,15 @@ test_config_settings(void)
 				ok_buffers = 0;
 
 
+	/*
+	 * Need to determine working DSM implementation first so that subsequent
+	 * tests don't fail because DSM setting doesn't work.
+	 */
+	printf(_("selecting dynamic shared memory implementation ... "));
+	fflush(stdout);
+	dynamic_shared_memory_type = choose_dsm_implementation();
+	printf("%s\n", dynamic_shared_memory_type);
+
 	printf(_("selecting default max_connections ... "));
 	fflush(stdout);
 
@@ -996,10 +1005,11 @@ test_config_settings(void)
 				 "\"%s\" --boot -x0 %s "
 				 "-c max_connections=%d "
 				 "-c shared_buffers=%d "
-				 "-c dynamic_shared_memory_type=none "
+				 "-c dynamic_shared_memory_type=%s "
 				 "< \"%s\" > \"%s\" 2>&1",
 				 backend_exec, boot_options,
 				 test_conns, test_buffs,
+				 dynamic_shared_memory_type,
 				 DEVNULL, DEVNULL);
 		status = system(cmd);
 		if (status == 0)
@@ -1031,10 +1041,11 @@ test_config_settings(void)
 				 "\"%s\" --boot -x0 %s "
 				 "-c max_connections=%d "
 				 "-c shared_buffers=%d "
-				 "-c dynamic_shared_memory_type=none "
+				 "-c dynamic_shared_memory_type=%s "
 				 "< \"%s\" > \"%s\" 2>&1",
 				 backend_exec, boot_options,
 				 n_connections, test_buffs,
+				 dynamic_shared_memory_type,
 				 DEVNULL, DEVNULL);
 		status = system(cmd);
 		if (status == 0)
@@ -1046,11 +1057,6 @@ test_config_settings(void)
 		printf("%dMB\n", (n_buffers * (BLCKSZ / 1024)) / 1024);
 	else
 		printf("%dkB\n", n_buffers * (BLCKSZ / 1024));
-
-	printf(_("selecting dynamic shared memory implementation ... "));
-	fflush(stdout);
-	dynamic_shared_memory_type = choose_dsm_implementation();
-	printf("%s\n", dynamic_shared_memory_type);
 }
 
 /*

src/include/storage/dsm_impl.h

@@ -14,7 +14,6 @@
 #define DSM_IMPL_H
 
 /* Dynamic shared memory implementations. */
-#define DSM_IMPL_NONE			0
 #define DSM_IMPL_POSIX			1
 #define DSM_IMPL_SYSV			2
 #define DSM_IMPL_WINDOWS		3