PostgresMain(int argc, char *argv[],
			 const char *dbname,
			 const char *username)
{
	int			firstchar;
	StringInfoData input_message;
	sigjmp_buf	local_sigjmp_buf;
	volatile bool send_ready_for_query = true;

	/* Initialize startup process environment if necessary. */
	if (!IsUnderPostmaster)
		InitStandaloneProcess(argv[0]);

	SetProcessingMode(InitProcessing);

	/*
	 * Set default values for command-line options.
	 */
	if (!IsUnderPostmaster)
		InitializeGUCOptions();

	/*
	 * Parse command-line options.
	 */
	process_postgres_switches(argc, argv, PGC_POSTMASTER, &dbname);

	/* Must have gotten a database name, or have a default (the username) */
	if (dbname == NULL)
	{
		dbname = username;
		if (dbname == NULL)
			ereport(FATAL,
					(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
					 errmsg("%s: no database nor user name specified",
							progname)));
	}

	/* Acquire configuration parameters, unless inherited from postmaster */
	if (!IsUnderPostmaster)
	{
		if (!SelectConfigFiles(userDoption, progname))
			proc_exit(1);
	}

	/*
	 * Set up signal handlers and masks.
	 *
	 * Note that postmaster blocked all signals before forking child process,
	 * so there is no race condition whereby we might receive a signal before
	 * we have set up the handler.
	 *
	 * Also note: it's best not to use any signals that are SIG_IGNored in the
	 * postmaster.  If such a signal arrives before we are able to change the
	 * handler to non-SIG_IGN, it'll get dropped.  Instead, make a dummy
	 * handler in the postmaster to reserve the signal. (Of course, this isn't
	 * an issue for signals that are locally generated, such as SIGALRM and
	 * SIGPIPE.)
	 */
	if (am_walsender)
		WalSndSignals();
	else
	{
		pqsignal(SIGHUP, SigHupHandler);		/* set flag to read config
												 * file */
		pqsignal(SIGINT, StatementCancelHandler);		/* cancel current query */
		pqsignal(SIGTERM, die); /* cancel current query and exit */

		/*
		 * In a standalone backend, SIGQUIT can be generated from the keyboard
		 * easily, while SIGTERM cannot, so we make both signals do die()
		 * rather than quickdie().
		 */
		if (IsUnderPostmaster)
			pqsignal(SIGQUIT, quickdie);		/* hard crash time */
		else
			pqsignal(SIGQUIT, die);		/* cancel current query and exit */
		InitializeTimeouts();	/* establishes SIGALRM handler */

		/*
		 * Ignore failure to write to frontend. Note: if frontend closes
		 * connection, we will notice it and exit cleanly when control next
		 * returns to outer loop.  This seems safer than forcing exit in the
		 * midst of output during who-knows-what operation...
		 */
		pqsignal(SIGPIPE, SIG_IGN);
		pqsignal(SIGUSR1, procsignal_sigusr1_handler);
		pqsignal(SIGUSR2, SIG_IGN);
		pqsignal(SIGFPE, FloatExceptionHandler);

		/*
		 * Reset some signals that are accepted by postmaster but not by
		 * backend
		 */
		pqsignal(SIGCHLD, SIG_DFL);		/* system() requires this on some
										 * platforms */
	}

	pqinitmask();

	if (IsUnderPostmaster)
	{
		/* We allow SIGQUIT (quickdie) at all times */
		sigdelset(&BlockSig, SIGQUIT);
	}

	PG_SETMASK(&BlockSig);		/* block everything except SIGQUIT */

	if (!IsUnderPostmaster)
	{
		/*
		 * Validate we have been given a reasonable-looking DataDir (if under
		 * postmaster, assume postmaster did this already).
		 */
		Assert(DataDir);
		ValidatePgVersion(DataDir);

		/* Change into DataDir (if under postmaster, was done already) */
		ChangeToDataDir();

		/*
		 * Create lockfile for data directory.
		 */
		CreateDataDirLockFile(false);

		/* Initialize MaxBackends (if under postmaster, was done already) */
		InitializeMaxBackends();
	}

	/* Early initialization */
	BaseInit();

	/*
	 * Create a per-backend PGPROC struct in shared memory, except in the
	 * EXEC_BACKEND case where this was done in SubPostmasterMain. We must do
	 * this before we can use LWLocks (and in the EXEC_BACKEND case we already
	 * had to do some stuff with LWLocks).
	 */
#ifdef EXEC_BACKEND
	if (!IsUnderPostmaster)
		InitProcess();
#else
	InitProcess();
#endif

	/* We need to allow SIGINT, etc during the initial transaction */
	PG_SETMASK(&UnBlockSig);

	/*
	 * General initialization.
	 *
	 * NOTE: if you are tempted to add code in this vicinity, consider putting
	 * it inside InitPostgres() instead.  In particular, anything that
	 * involves database access should be there, not here.
	 */
	InitPostgres(dbname, InvalidOid, username, NULL);

	/*
	 * If the PostmasterContext is still around, recycle the space; we don't
	 * need it anymore after InitPostgres completes.  Note this does not trash
	 * *MyProcPort, because ConnCreate() allocated that space with malloc()
	 * ... else we'd need to copy the Port data first.  Also, subsidiary data
	 * such as the username isn't lost either; see ProcessStartupPacket().
	 */
	if (PostmasterContext)
	{
		MemoryContextDelete(PostmasterContext);
		PostmasterContext = NULL;
	}

	SetProcessingMode(NormalProcessing);

	/*
	 * Now all GUC states are fully set up.  Report them to client if
	 * appropriate.
	 */
	BeginReportingGUCOptions();

	/*
	 * Also set up handler to log session end; we have to wait till now to be
	 * sure Log_disconnections has its final value.
	 */
	if (IsUnderPostmaster && Log_disconnections)
		on_proc_exit(log_disconnections, 0);

	/* Perform initialization specific to a WAL sender process. */
	if (am_walsender)
		InitWalSender();

	/*
	 * process any libraries that should be preloaded at backend start (this
	 * likewise can't be done until GUC settings are complete)
	 */
	process_session_preload_libraries();

	/*
	 * Send this backend's cancellation info to the frontend.
	 */
	if (whereToSendOutput == DestRemote &&
		PG_PROTOCOL_MAJOR(FrontendProtocol) >= 2)
	{
		StringInfoData buf;

		pq_beginmessage(&buf, 'K');
		pq_sendint(&buf, (int32) MyProcPid, sizeof(int32));
		pq_sendint(&buf, (int32) MyCancelKey, sizeof(int32));
		pq_endmessage(&buf);
		/* Need not flush since ReadyForQuery will do it. */
	}

	/* Welcome banner for standalone case */
	if (whereToSendOutput == DestDebug)
		printf("\nPostgreSQL stand-alone backend %s\n", PG_VERSION);

	/*
	 * Create the memory context we will use in the main loop.
	 *
	 * MessageContext is reset once per iteration of the main loop, ie, upon
	 * completion of processing of each command message from the client.
	 */
	MessageContext = AllocSetContextCreate(TopMemoryContext,
										   "MessageContext",
										   ALLOCSET_DEFAULT_MINSIZE,
										   ALLOCSET_DEFAULT_INITSIZE,
										   ALLOCSET_DEFAULT_MAXSIZE);

	/*
	 * Remember stand-alone backend startup time
	 */
	if (!IsUnderPostmaster)
		PgStartTime = GetCurrentTimestamp();

	/*
	 * POSTGRES main processing loop begins here
	 *
	 * If an exception is encountered, processing resumes here so we abort the
	 * current transaction and start a new one.
	 *
	 * You might wonder why this isn't coded as an infinite loop around a
	 * PG_TRY construct.  The reason is that this is the bottom of the
	 * exception stack, and so with PG_TRY there would be no exception handler
	 * in force at all during the CATCH part.  By leaving the outermost setjmp
	 * always active, we have at least some chance of recovering from an error
	 * during error recovery.  (If we get into an infinite loop thereby, it
	 * will soon be stopped by overflow of elog.c's internal state stack.)
	 *
	 * Note that we use sigsetjmp(..., 1), so that this function's signal mask
	 * (to wit, UnBlockSig) will be restored when longjmp'ing to here.  This
	 * is essential in case we longjmp'd out of a signal handler on a platform
	 * where that leaves the signal blocked.  It's not redundant with the
	 * unblock in AbortTransaction() because the latter is only called if we
	 * were inside a transaction.
	 */

	if (sigsetjmp(local_sigjmp_buf, 1) != 0)
	{
		/*
		 * NOTE: if you are tempted to add more code in this if-block,
		 * consider the high probability that it should be in
		 * AbortTransaction() instead.  The only stuff done directly here
		 * should be stuff that is guaranteed to apply *only* for outer-level
		 * error recovery, such as adjusting the FE/BE protocol status.
		 */

		/* Since not using PG_TRY, must reset error stack by hand */
		error_context_stack = NULL;

		/* Prevent interrupts while cleaning up */
		HOLD_INTERRUPTS();

		/*
		 * Forget any pending QueryCancel request, since we're returning to
		 * the idle loop anyway, and cancel any active timeout requests.  (In
		 * future we might want to allow some timeout requests to survive, but
		 * at minimum it'd be necessary to do reschedule_timeouts(), in case
		 * we got here because of a query cancel interrupting the SIGALRM
		 * interrupt handler.)	Note in particular that we must clear the
		 * statement and lock timeout indicators, to prevent any future plain
		 * query cancels from being misreported as timeouts in case we're
		 * forgetting a timeout cancel.
		 */
		disable_all_timeouts(false);
		QueryCancelPending = false;		/* second to avoid race condition */

		/*
		 * Turn off these interrupts too.  This is only needed here and not in
		 * other exception-catching places since these interrupts are only
		 * enabled while we wait for client input.
		 */
		DoingCommandRead = false;
		DisableNotifyInterrupt();
		DisableCatchupInterrupt();

		/* Make sure libpq is in a good state */
		pq_comm_reset();

		/* Report the error to the client and/or server log */
		EmitErrorReport();

		/*
		 * Make sure debug_query_string gets reset before we possibly clobber
		 * the storage it points at.
		 */
		debug_query_string = NULL;

		/*
		 * Abort the current transaction in order to recover.
		 */
		AbortCurrentTransaction();

		if (am_walsender)
			WalSndErrorCleanup();

		/*
		 * We can't release replication slots inside AbortTransaction() as we
		 * need to be able to start and abort transactions while having a slot
		 * acquired. But we never need to hold them across top level errors,
		 * so releasing here is fine. There's another cleanup in ProcKill()
		 * ensuring we'll correctly cleanup on FATAL errors as well.
		 */
		if (MyReplicationSlot != NULL)
			ReplicationSlotRelease();

		/*
		 * Now return to normal top-level context and clear ErrorContext for
		 * next time.
		 */
		MemoryContextSwitchTo(TopMemoryContext);
		FlushErrorState();

		/*
		 * If we were handling an extended-query-protocol message, initiate
		 * skip till next Sync.  This also causes us not to issue
		 * ReadyForQuery (until we get Sync).
		 */
		if (doing_extended_query_message)
			ignore_till_sync = true;

		/* We don't have a transaction command open anymore */
		xact_started = false;

		/* Now we can allow interrupts again */
		RESUME_INTERRUPTS();
	}

	/* We can now handle ereport(ERROR) */
	PG_exception_stack = &local_sigjmp_buf;

	if (!ignore_till_sync)
		send_ready_for_query = true;	/* initially, or after error */

	/*
	 * Non-error queries loop here.
	 */

	for (;;)
	{
		/*
		 * At top of loop, reset extended-query-message flag, so that any
		 * errors encountered in "idle" state don't provoke skip.
		 */
		doing_extended_query_message = false;

		/*
		 * Release storage left over from prior query cycle, and create a new
		 * query input buffer in the cleared MessageContext.
		 */
		MemoryContextSwitchTo(MessageContext);
		MemoryContextResetAndDeleteChildren(MessageContext);

		initStringInfo(&input_message);

		/*
		 * (1) If we've reached idle state, tell the frontend we're ready for
		 * a new query.
		 *
		 * Note: this includes fflush()'ing the last of the prior output.
		 *
		 * This is also a good time to send collected statistics to the
		 * collector, and to update the PS stats display.  We avoid doing
		 * those every time through the message loop because it'd slow down
		 * processing of batched messages, and because we don't want to report
		 * uncommitted updates (that confuses autovacuum).  The notification
		 * processor wants a call too, if we are not in a transaction block.
		 */
		if (send_ready_for_query)
		{
			if (IsAbortedTransactionBlockState())
			{
				set_ps_display("idle in transaction (aborted)", false);
				pgstat_report_activity(STATE_IDLEINTRANSACTION_ABORTED, NULL);
			}
			else if (IsTransactionOrTransactionBlock())
			{
				set_ps_display("idle in transaction", false);
				pgstat_report_activity(STATE_IDLEINTRANSACTION, NULL);
			}
			else
			{
				ProcessCompletedNotifies();
				pgstat_report_stat(false);

				set_ps_display("idle", false);
				pgstat_report_activity(STATE_IDLE, NULL);
			}

			ReadyForQuery(whereToSendOutput);
			send_ready_for_query = false;
		}

		/*
		 * (2) Allow asynchronous signals to be executed immediately if they
		 * come in while we are waiting for client input. (This must be
		 * conditional since we don't want, say, reads on behalf of COPY FROM
		 * STDIN doing the same thing.)
		 */
		DoingCommandRead = true;

		/*
		 * (3) read a command (loop blocks here)
		 */
		firstchar = ReadCommand(&input_message);

		/*
		 * (4) disable async signal conditions again.
		 */
		DoingCommandRead = false;

		/*
		 * (5) check for any other interesting events that happened while we
		 * slept.
		 */
		if (got_SIGHUP)
		{
			got_SIGHUP = false;
			ProcessConfigFile(PGC_SIGHUP);
		}

		/*
		 * (6) process the command.  But ignore it if we're skipping till
		 * Sync.
		 */
		if (ignore_till_sync && firstchar != EOF)
			continue;

		switch (firstchar)
		{
			case 'Q':			/* simple query */
				{
					const char *query_string;

					/* Set statement_timestamp() */
					SetCurrentStatementStartTimestamp();

					query_string = pq_getmsgstring(&input_message);
					pq_getmsgend(&input_message);

					if (am_walsender)
						exec_replication_command(query_string);
					else
						exec_simple_query(query_string);

					send_ready_for_query = true;
				}
				break;

			case 'P':			/* parse */
				{
					const char *stmt_name;
					const char *query_string;
					int			numParams;
					Oid		   *paramTypes = NULL;

					forbidden_in_wal_sender(firstchar);

					/* Set statement_timestamp() */
					SetCurrentStatementStartTimestamp();

					stmt_name = pq_getmsgstring(&input_message);
					query_string = pq_getmsgstring(&input_message);
					numParams = pq_getmsgint(&input_message, 2);
					if (numParams > 0)
					{
						int			i;

						paramTypes = (Oid *) palloc(numParams * sizeof(Oid));
						for (i = 0; i < numParams; i++)
							paramTypes[i] = pq_getmsgint(&input_message, 4);
					}
					pq_getmsgend(&input_message);

					exec_parse_message(query_string, stmt_name,
									   paramTypes, numParams);
				}
				break;

			case 'B':			/* bind */
				forbidden_in_wal_sender(firstchar);

				/* Set statement_timestamp() */
				SetCurrentStatementStartTimestamp();

				/*
				 * this message is complex enough that it seems best to put
				 * the field extraction out-of-line
				 */
				exec_bind_message(&input_message);
				break;

			case 'E':			/* execute */
				{
					const char *portal_name;
					int			max_rows;

					forbidden_in_wal_sender(firstchar);

					/* Set statement_timestamp() */
					SetCurrentStatementStartTimestamp();

					portal_name = pq_getmsgstring(&input_message);
					max_rows = pq_getmsgint(&input_message, 4);
					pq_getmsgend(&input_message);

					exec_execute_message(portal_name, max_rows);
				}
				break;

			case 'F':			/* fastpath function call */
				forbidden_in_wal_sender(firstchar);

				/* Set statement_timestamp() */
				SetCurrentStatementStartTimestamp();

				/* Report query to various monitoring facilities. */
				pgstat_report_activity(STATE_FASTPATH, NULL);
				set_ps_display("<FASTPATH>", false);

				/* start an xact for this function invocation */
				start_xact_command();

				/*
				 * Note: we may at this point be inside an aborted
				 * transaction.  We can't throw error for that until we've
				 * finished reading the function-call message, so
				 * HandleFunctionRequest() must check for it after doing so.
				 * Be careful not to do anything that assumes we're inside a
				 * valid transaction here.
				 */

				/* switch back to message context */
				MemoryContextSwitchTo(MessageContext);

				if (HandleFunctionRequest(&input_message) == EOF)
				{
					/* lost frontend connection during F message input */

					/*
					 * Reset whereToSendOutput to prevent ereport from
					 * attempting to send any more messages to client.
					 */
					if (whereToSendOutput == DestRemote)
						whereToSendOutput = DestNone;

					proc_exit(0);
				}

				/* commit the function-invocation transaction */
				finish_xact_command();

				send_ready_for_query = true;
				break;

			case 'C':			/* close */
				{
					int			close_type;
					const char *close_target;

					forbidden_in_wal_sender(firstchar);

					close_type = pq_getmsgbyte(&input_message);
					close_target = pq_getmsgstring(&input_message);
					pq_getmsgend(&input_message);

					switch (close_type)
					{
						case 'S':
							if (close_target[0] != '\0')
								DropPreparedStatement(close_target, false);
							else
							{
								/* special-case the unnamed statement */
								drop_unnamed_stmt();
							}
							break;
						case 'P':
							{
								Portal		portal;

								portal = GetPortalByName(close_target);
								if (PortalIsValid(portal))
									PortalDrop(portal, false);
							}
							break;
						default:
							ereport(ERROR,
									(errcode(ERRCODE_PROTOCOL_VIOLATION),
								   errmsg("invalid CLOSE message subtype %d",
										  close_type)));
							break;
					}

					if (whereToSendOutput == DestRemote)
						pq_putemptymessage('3');		/* CloseComplete */
				}
				break;

			case 'D':			/* describe */
				{
					int			describe_type;
					const char *describe_target;

					forbidden_in_wal_sender(firstchar);

					/* Set statement_timestamp() (needed for xact) */
					SetCurrentStatementStartTimestamp();

					describe_type = pq_getmsgbyte(&input_message);
					describe_target = pq_getmsgstring(&input_message);
					pq_getmsgend(&input_message);

					switch (describe_type)
					{
						case 'S':
							exec_describe_statement_message(describe_target);
							break;
						case 'P':
							exec_describe_portal_message(describe_target);
							break;
						default:
							ereport(ERROR,
									(errcode(ERRCODE_PROTOCOL_VIOLATION),
								errmsg("invalid DESCRIBE message subtype %d",
									   describe_type)));
							break;
					}
				}
				break;

			case 'H':			/* flush */
				pq_getmsgend(&input_message);
				if (whereToSendOutput == DestRemote)
					pq_flush();
				break;

			case 'S':			/* sync */
				pq_getmsgend(&input_message);
				finish_xact_command();
				send_ready_for_query = true;
				break;

				/*
				 * 'X' means that the frontend is closing down the socket. EOF
				 * means unexpected loss of frontend connection. Either way,
				 * perform normal shutdown.
				 */
			case 'X':
			case EOF:

				/*
				 * Reset whereToSendOutput to prevent ereport from attempting
				 * to send any more messages to client.
				 */
				if (whereToSendOutput == DestRemote)
					whereToSendOutput = DestNone;

				/*
				 * NOTE: if you are tempted to add more code here, DON'T!
				 * Whatever you had in mind to do should be set up as an
				 * on_proc_exit or on_shmem_exit callback, instead. Otherwise
				 * it will fail to be called during other backend-shutdown
				 * scenarios.
				 */
				proc_exit(0);

			case 'd':			/* copy data */
			case 'c':			/* copy done */
			case 'f':			/* copy fail */

				/*
				 * Accept but ignore these messages, per protocol spec; we
				 * probably got here because a COPY failed, and the frontend
				 * is still sending data.
				 */
				break;

			default:
				ereport(FATAL,
						(errcode(ERRCODE_PROTOCOL_VIOLATION),
						 errmsg("invalid frontend message type %d",
								firstchar)));
		}
	}							/* end of input-reading loop */
}