Set max_safe_fds whenever we create shared memory and semaphores.

tglsfdc · tglsfdc · commit 21fb39cb0793 · 2024-12-17T12:23:26.000-05:00
Formerly we skipped this in bootstrap/check mode and in single-user mode. That's bad in check mode because it may allow accepting a value of max_connections that doesn't actually work: on platforms where semaphores consume file descriptors, there may not be enough free FDs left over to satisfy fd.c, causing postmaster start to fail. It's also not great in single-user mode, because fd.c will operate with just the minimum allowable value of max_safe_fds, resulting in excess file open/close overhead if anything moderately complicated is done in single-user mode. (There may be some penalty for bootstrap mode too, though probably not much.) Discussion: https://postgr.es/m/2081982.1734393311@sss.pgh.pa.us
diff --git a/src/backend/bootstrap/bootstrap.c b/src/backend/bootstrap/bootstrap.c
@@ -334,6 +334,12 @@ BootstrapModeMain(int argc, char *argv[], bool check_only)
 
 	CreateSharedMemoryAndSemaphores();
 
+	/*
+	 * Estimate number of openable files.  This is essential too in --check
+	 * mode, because on some platforms semaphores count as open files.
+	 */
+	set_max_safe_fds();
+
 	/*
 	 * XXX: It might make sense to move this into its own function at some
 	 * point. Right now it seems like it'd cause more code duplication than
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
@@ -4099,8 +4099,18 @@ PostgresSingleUserMain(int argc, char *argv[],
 	 */
 	InitializeWalConsistencyChecking();
 
+	/*
+	 * Create shared memory etc.  (Nothing's really "shared" in single-user
+	 * mode, but we must have these data structures anyway.)
+	 */
 	CreateSharedMemoryAndSemaphores();
 
+	/*
+	 * Estimate number of openable files.  This must happen after setting up
+	 * semaphores, because on some platforms semaphores count as open files.
+	 */
+	set_max_safe_fds();
+
 	/*
 	 * Remember stand-alone backend startup time,roughly at the same point
 	 * during startup that postmaster does so.
