diff --git a/src/bin/initdb/initdb.c b/src/bin/initdb/initdb.c
index a6eb0d8061..ebe8a67c0b 100644
--- a/src/bin/initdb/initdb.c
+++ b/src/bin/initdb/initdb.c
@@ -56,6 +56,10 @@
 #include <signal.h>
 #include <time.h>
 
+#ifdef HAVE_SHM_OPEN
+#include "sys/mman.h"
+#endif
+
 #include "mb/pg_wchar.h"
 #include "getaddrinfo.h"
 #include "getopt_long.h"
@@ -150,6 +154,7 @@ static char *pgdata_native;
 /* defaults */
 static int	n_connections = 10;
 static int	n_buffers = 50;
+static char *dynamic_shared_memory_type = NULL;
 
 /*
  * Warning messages for authentication methods
@@ -1076,6 +1081,50 @@ set_null_conf(void)
 	free(path);
 }
 
+/*
+ * Determine which dynamic shared memory implementation should be used on
+ * this platform.  POSIX shared memory is preferable because the default
+ * allocation limits are much higher than the limits for System V on most
+ * systems that support both, but the fact that a platform has shm_open
+ * doesn't guarantee that that call will succeed when attempted.  So, we
+ * attempt to reproduce what the postmaster will do when allocating a POSIX
+ * segment in dsm_impl.c; if it doesn't work, we assume it won't work for
+ * the postmaster either, and configure the cluster for System V shared
+ * memory instead.
+ */
+static char *
+choose_dsm_implementation(void)
+{
+#ifdef HAVE_SHM_OPEN
+	int		ntries = 10;
+
+	while (ntries > 0)
+	{
+		uint32	handle;
+		char 	name[64];
+		int		fd;
+
+		handle = random();
+		snprintf(name, 64, "/PostgreSQL.%u", handle);
+		if ((fd = shm_open(name, O_CREAT | O_RDWR | O_EXCL, 0600)) != -1)
+		{
+			close(fd);
+			shm_unlink(name);
+			return "posix";
+		}
+		if (errno != EEXIST)
+			break;
+		--ntries;
+	}
+#endif
+
+#ifdef WIN32
+	return "windows";
+#else
+	return "sysv";
+#endif
+}
+
 /*
  * Determine platform-specific config settings
  *
@@ -1157,6 +1206,7 @@ test_config_settings(void)
 				 SYSTEMQUOTE "\"%s\" --boot -x0 %s "
 				 "-c max_connections=%d "
 				 "-c shared_buffers=%d "
+				 "-c dynamic_shared_memory_type=none "
 				 "< \"%s\" > \"%s\" 2>&1" SYSTEMQUOTE,
 				 backend_exec, boot_options,
 				 n_connections, test_buffs,
@@ -1171,6 +1221,11 @@ 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);
 }
 
 /*
@@ -1265,6 +1320,11 @@ setup_config(void)
 		conflines = replace_token(conflines, "#log_timezone = 'GMT'", repltok);
 	}
 
+	snprintf(repltok, sizeof(repltok), "dynamic_shared_memory_type = %s",
+			 dynamic_shared_memory_type);
+	conflines = replace_token(conflines, "#dynamic_shared_memory_type = posix",
+							  repltok);
+
 	snprintf(path, sizeof(path), "%s/postgresql.conf", pg_data);
 
 	writefile(path, conflines);