Rearrange postmaster's startup sequence for better syslogger results.

This is a second try at what commit 57431a911 tried to do, namely,
launch the syslogger before we open postmaster sockets so that our
messages about the sockets end up in the syslogger files.  That
commit fell foul of a bunch of subtle issues caused by trying to
launch a postmaster child process before creating shared memory.
Rather than messing with that interaction, let's postpone opening
the sockets till after we launch the syslogger.

This would not have been terribly safe before commit 7de19fbc0,
because we relied on socket opening to detect whether any competing
postmasters were using the same port number.  But now that we choose
IPC keys without regard to the port number, there's no interaction
to worry about.

Also delay creation of the external PID file (if requested) till after
the sockets are open, since external code could plausibly be relying
on that ordering of events.  And postpone most of the work of
RemovePgTempFiles() so that that potentially-slow processing still
happens after we make the external PID file.  We have to be a bit
careful about that last though: as noted in the discussion subsequent to
bug #15804, EXEC_BACKEND builds still have to clear the parameter-file
temp dir before launching the syslogger.

Patch by me; thanks to Michael Paquier for review/testing.

Discussion: https://postgr.es/m/15804-3721117bf40fb654@postgresql.org

src/backend/postmaster/postmaster.c

@@ -993,7 +993,113 @@ PostmasterMain(int argc, char *argv[])
 	 */
 	InitializeMaxBackends();
 
-	/* Report server startup in log */
+	/*
+	 * Set up shared memory and semaphores.
+	 */
+	reset_shared();
+
+	/*
+	 * 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();
+
+	/*
+	 * Set reference point for stack-depth checking.
+	 */
+	set_stack_base();
+
+	/*
+	 * Initialize pipe (or process handle on Windows) that allows children to
+	 * wake up from sleep on postmaster death.
+	 */
+	InitPostmasterDeathWatchHandle();
+
+#ifdef WIN32
+
+	/*
+	 * Initialize I/O completion port used to deliver list of dead children.
+	 */
+	win32ChildQueue = CreateIoCompletionPort(INVALID_HANDLE_VALUE, NULL, 0, 1);
+	if (win32ChildQueue == NULL)
+		ereport(FATAL,
+				(errmsg("could not create I/O completion port for child queue")));
+#endif
+
+#ifdef EXEC_BACKEND
+	/* Write out nondefault GUC settings for child processes to use */
+	write_nondefault_variables(PGC_POSTMASTER);
+
+	/*
+	 * Clean out the temp directory used to transmit parameters to child
+	 * processes (see internal_forkexec, below).  We must do this before
+	 * launching any child processes, else we have a race condition: we could
+	 * remove a parameter file before the child can read it.  It should be
+	 * safe to do so now, because we verified earlier that there are no
+	 * conflicting Postgres processes in this data directory.
+	 */
+	RemovePgTempFilesInDir(PG_TEMP_FILES_DIR, true, false);
+#endif
+
+	/*
+	 * Forcibly remove the files signaling a standby promotion request.
+	 * Otherwise, the existence of those files triggers a promotion too early,
+	 * whether a user wants that or not.
+	 *
+	 * This removal of files is usually unnecessary because they can exist
+	 * only during a few moments during a standby promotion. However there is
+	 * a race condition: if pg_ctl promote is executed and creates the files
+	 * during a promotion, the files can stay around even after the server is
+	 * brought up to new master. Then, if new standby starts by using the
+	 * backup taken from that master, the files can exist at the server
+	 * startup and should be removed in order to avoid an unexpected
+	 * promotion.
+	 *
+	 * Note that promotion signal files need to be removed before the startup
+	 * process is invoked. Because, after that, they can be used by
+	 * postmaster's SIGUSR1 signal handler.
+	 */
+	RemovePromoteSignalFiles();
+
+	/* Do the same for logrotate signal file */
+	RemoveLogrotateSignalFiles();
+
+	/* Remove any outdated file holding the current log filenames. */
+	if (unlink(LOG_METAINFO_DATAFILE) < 0 && errno != ENOENT)
+		ereport(LOG,
+				(errcode_for_file_access(),
+				 errmsg("could not remove file \"%s\": %m",
+						LOG_METAINFO_DATAFILE)));
+
+	/*
+	 * If enabled, start up syslogger collection subprocess
+	 */
+	SysLoggerPID = SysLogger_Start();
+
+	/*
+	 * Reset whereToSendOutput from DestDebug (its starting state) to
+	 * DestNone. This stops ereport from sending log messages to stderr unless
+	 * Log_destination permits.  We don't do this until the postmaster is
+	 * fully launched, since startup failures may as well be reported to
+	 * stderr.
+	 *
+	 * If we are in fact disabling logging to stderr, first emit a log message
+	 * saying so, to provide a breadcrumb trail for users who may not remember
+	 * that their logging is configured to go somewhere else.
+	 */
+	if (!(Log_destination & LOG_DESTINATION_STDERR))
+		ereport(LOG,
+				(errmsg("ending log output to stderr"),
+				 errhint("Future log output will go to log destination \"%s\".",
+						 Log_destination_string)));
+
+	whereToSendOutput = DestNone;
+
+	/*
+	 * Report server startup in log.  While we could emit this much earlier,
+	 * it seems best to do so after starting the log collector, if we intend
+	 * to use one.
+	 */
 	ereport(LOG,
 			(errmsg("starting %s", PG_VERSION_STR)));
 
@@ -1172,51 +1278,13 @@ PostmasterMain(int argc, char *argv[])
 	if (!listen_addr_saved)
 		AddToDataDirLockFile(LOCK_FILE_LINE_LISTEN_ADDR, "");
 
-	/*
-	 * Set up shared memory and semaphores.
-	 */
-	reset_shared();
-
-	/*
-	 * 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();
-
-	/*
-	 * Set reference point for stack-depth checking.
-	 */
-	set_stack_base();
-
-	/*
-	 * Initialize pipe (or process handle on Windows) that allows children to
-	 * wake up from sleep on postmaster death.
-	 */
-	InitPostmasterDeathWatchHandle();
-
-#ifdef WIN32
-
-	/*
-	 * Initialize I/O completion port used to deliver list of dead children.
-	 */
-	win32ChildQueue = CreateIoCompletionPort(INVALID_HANDLE_VALUE, NULL, 0, 1);
-	if (win32ChildQueue == NULL)
-		ereport(FATAL,
-				(errmsg("could not create I/O completion port for child queue")));
-#endif
-
 	/*
 	 * Record postmaster options.  We delay this till now to avoid recording
-	 * bogus options (eg, NBuffers too high for available memory).
+	 * bogus options (eg, unusable port number).
 	 */
 	if (!CreateOptsFile(argc, argv, my_exec_path))
 		ExitPostmaster(1);
 
-#ifdef EXEC_BACKEND
-	/* Write out nondefault GUC settings for child processes to use */
-	write_nondefault_variables(PGC_POSTMASTER);
-#endif
-
 	/*
 	 * Write the external PID file if requested
 	 */
@@ -1247,60 +1315,6 @@ PostmasterMain(int argc, char *argv[])
 	 */
 	RemovePgTempFiles();
 
-	/*
-	 * Forcibly remove the files signaling a standby promotion request.
-	 * Otherwise, the existence of those files triggers a promotion too early,
-	 * whether a user wants that or not.
-	 *
-	 * This removal of files is usually unnecessary because they can exist
-	 * only during a few moments during a standby promotion. However there is
-	 * a race condition: if pg_ctl promote is executed and creates the files
-	 * during a promotion, the files can stay around even after the server is
-	 * brought up to new master. Then, if new standby starts by using the
-	 * backup taken from that master, the files can exist at the server
-	 * startup and should be removed in order to avoid an unexpected
-	 * promotion.
-	 *
-	 * Note that promotion signal files need to be removed before the startup
-	 * process is invoked. Because, after that, they can be used by
-	 * postmaster's SIGUSR1 signal handler.
-	 */
-	RemovePromoteSignalFiles();
-
-	/* Do the same for logrotate signal file */
-	RemoveLogrotateSignalFiles();
-
-	/* Remove any outdated file holding the current log filenames. */
-	if (unlink(LOG_METAINFO_DATAFILE) < 0 && errno != ENOENT)
-		ereport(LOG,
-				(errcode_for_file_access(),
-				 errmsg("could not remove file \"%s\": %m",
-						LOG_METAINFO_DATAFILE)));
-
-	/*
-	 * If enabled, start up syslogger collection subprocess
-	 */
-	SysLoggerPID = SysLogger_Start();
-
-	/*
-	 * Reset whereToSendOutput from DestDebug (its starting state) to
-	 * DestNone. This stops ereport from sending log messages to stderr unless
-	 * Log_destination permits.  We don't do this until the postmaster is
-	 * fully launched, since startup failures may as well be reported to
-	 * stderr.
-	 *
-	 * If we are in fact disabling logging to stderr, first emit a log message
-	 * saying so, to provide a breadcrumb trail for users who may not remember
-	 * that their logging is configured to go somewhere else.
-	 */
-	if (!(Log_destination & LOG_DESTINATION_STDERR))
-		ereport(LOG,
-				(errmsg("ending log output to stderr"),
-				 errhint("Future log output will go to log destination \"%s\".",
-						 Log_destination_string)));
-
-	whereToSendOutput = DestNone;
-
 	/*
 	 * Initialize stats collection subsystem (this does NOT start the
 	 * collector process!)

src/backend/storage/file/fd.c

@@ -307,8 +307,6 @@ static int	FreeDesc(AllocateDesc *desc);
 
 static void AtProcExit_Files(int code, Datum arg);
 static void CleanupTempFiles(bool isCommit, bool isProcExit);
-static void RemovePgTempFilesInDir(const char *tmpdirname, bool missing_ok,
-								   bool unlink_all);
 static void RemovePgTempRelationFiles(const char *tsdirname);
 static void RemovePgTempRelationFilesInDbspace(const char *dbspacedirname);
 
@@ -2919,11 +2917,10 @@ RemovePgTempFiles(void)
 
 	/*
 	 * In EXEC_BACKEND case there is a pgsql_tmp directory at the top level of
-	 * DataDir as well.
+	 * DataDir as well.  However, that is *not* cleaned here because doing so
+	 * would create a race condition.  It's done separately, earlier in
+	 * postmaster startup.
 	 */
-#ifdef EXEC_BACKEND
-	RemovePgTempFilesInDir(PG_TEMP_FILES_DIR, true, false);
-#endif
 }
 
 /*
@@ -2941,7 +2938,7 @@ RemovePgTempFiles(void)
  * (These two flags could be replaced by one, but it seems clearer to keep
  * them separate.)
  */
-static void
+void
 RemovePgTempFilesInDir(const char *tmpdirname, bool missing_ok, bool unlink_all)
 {
 	DIR		   *temp_dir;

src/include/storage/fd.h

@@ -135,6 +135,8 @@ extern void AtEOXact_Files(bool isCommit);
 extern void AtEOSubXact_Files(bool isCommit, SubTransactionId mySubid,
 							  SubTransactionId parentSubid);
 extern void RemovePgTempFiles(void);
+extern void RemovePgTempFilesInDir(const char *tmpdirname, bool missing_ok,
+								   bool unlink_all);
 extern bool looks_like_temp_rel_name(const char *name);
 
 extern int	pg_fsync(int fd);

src/include/utils/pidfile.h

@@ -28,7 +28,8 @@
  *
  * Lines 6 and up are added via AddToDataDirLockFile() after initial file
  * creation; also, line 5 is initially empty and is changed after the first
- * Unix socket is opened.
+ * Unix socket is opened.  Onlookers should not assume that lines 4 and up
+ * are filled in any particular order.
  *
  * Socket lock file(s), if used, have the same contents as lines 1-5, with
  * line 5 being their own directory.