Exemplo n.º 1
0
/* Main loop of walsender process */
static int
WalSndLoop(void)
{
	char	   *output_message;
	bool		caughtup = false;

	/*
	 * Allocate buffer that will be used for each output message.  We do this
	 * just once to reduce palloc overhead.  The buffer must be made large
	 * enough for maximum-sized messages.
	 */
	output_message = palloc(1 + sizeof(WalDataMessageHeader) + MAX_SEND_SIZE);

	/*
	 * Allocate buffer that will be used for processing reply messages.  As
	 * above, do this just once to reduce palloc overhead.
	 */
	initStringInfo(&reply_message);

	/* Initialize the last reply timestamp */
	last_reply_timestamp = GetCurrentTimestamp();

	/* Loop forever, unless we get an error */
	for (;;)
	{
		/* Clear any already-pending wakeups */
		ResetLatch(&MyWalSnd->latch);

		/*
		 * Emergency bailout if postmaster has died.  This is to avoid the
		 * necessity for manual cleanup of all postmaster children.
		 */
		if (!PostmasterIsAlive())
			exit(1);

		/* Process any requests or signals received recently */
		if (got_SIGHUP)
		{
			got_SIGHUP = false;
			ProcessConfigFile(PGC_SIGHUP);
			SyncRepInitConfig();
		}

		/* Normal exit from the walsender is here */
		if (walsender_shutdown_requested)
		{
			/* Inform the standby that XLOG streaming is done */
			pq_puttextmessage('C', "COPY 0");
			pq_flush();

			proc_exit(0);
		}

		/* Check for input from the client */
		ProcessRepliesIfAny();

		/*
		 * If we don't have any pending data in the output buffer, try to send
		 * some more.  If there is some, we don't bother to call XLogSend
		 * again until we've flushed it ... but we'd better assume we are not
		 * caught up.
		 */
		if (!pq_is_send_pending())
			XLogSend(output_message, &caughtup);
		else
			caughtup = false;

		/* Try to flush pending output to the client */
		if (pq_flush_if_writable() != 0)
			break;

		/* If nothing remains to be sent right now ... */
		if (caughtup && !pq_is_send_pending())
		{
			/*
			 * If we're in catchup state, move to streaming.  This is an
			 * important state change for users to know about, since before
			 * this point data loss might occur if the primary dies and we
			 * need to failover to the standby. The state change is also
			 * important for synchronous replication, since commits that
			 * started to wait at that point might wait for some time.
			 */
			if (MyWalSnd->state == WALSNDSTATE_CATCHUP)
			{
				ereport(DEBUG1,
						(errmsg("standby \"%s\" has now caught up with primary",
								application_name)));
				WalSndSetState(WALSNDSTATE_STREAMING);
			}

			/*
			 * When SIGUSR2 arrives, we send any outstanding logs up to the
			 * shutdown checkpoint record (i.e., the latest record) and exit.
			 * This may be a normal termination at shutdown, or a promotion,
			 * the walsender is not sure which.
			 */
			if (walsender_ready_to_stop)
			{
				/* ... let's just be real sure we're caught up ... */
				XLogSend(output_message, &caughtup);
				if (caughtup && !pq_is_send_pending())
				{
					walsender_shutdown_requested = true;
					continue;		/* don't want to wait more */
				}
			}
		}

		/*
		 * We don't block if not caught up, unless there is unsent data
		 * pending in which case we'd better block until the socket is
		 * write-ready.  This test is only needed for the case where XLogSend
		 * loaded a subset of the available data but then pq_flush_if_writable
		 * flushed it all --- we should immediately try to send more.
		 */
		if (caughtup || pq_is_send_pending())
		{
			TimestampTz finish_time = 0;
			long		sleeptime = -1;
			int			wakeEvents;

			wakeEvents = WL_LATCH_SET | WL_POSTMASTER_DEATH |
				WL_SOCKET_READABLE;
			if (pq_is_send_pending())
				wakeEvents |= WL_SOCKET_WRITEABLE;

			/* Determine time until replication timeout */
			if (replication_timeout > 0)
			{
				long		secs;
				int			usecs;

				finish_time = TimestampTzPlusMilliseconds(last_reply_timestamp,
														  replication_timeout);
				TimestampDifference(GetCurrentTimestamp(),
									finish_time, &secs, &usecs);
				sleeptime = secs * 1000 + usecs / 1000;
				/* Avoid Assert in WaitLatchOrSocket if timeout is past */
				if (sleeptime < 0)
					sleeptime = 0;
				wakeEvents |= WL_TIMEOUT;
			}

			/* Sleep until something happens or replication timeout */
			WaitLatchOrSocket(&MyWalSnd->latch, wakeEvents,
							  MyProcPort->sock, sleeptime);

			/*
			 * Check for replication timeout.  Note we ignore the corner case
			 * possibility that the client replied just as we reached the
			 * timeout ... he's supposed to reply *before* that.
			 */
			if (replication_timeout > 0 &&
				GetCurrentTimestamp() >= finish_time)
			{
				/*
				 * Since typically expiration of replication timeout means
				 * communication problem, we don't send the error message to
				 * the standby.
				 */
				ereport(COMMERROR,
						(errmsg("terminating walsender process due to replication timeout")));
				break;
			}
		}
	}

	/*
	 * Get here on send failure.  Clean up and exit.
	 *
	 * Reset whereToSendOutput to prevent ereport from attempting to send any
	 * more messages to the standby.
	 */
	if (whereToSendOutput == DestRemote)
		whereToSendOutput = DestNone;

	proc_exit(0);
	return 1;					/* keep the compiler quiet */
}
Exemplo n.º 2
0
/* Main loop of walsender process */
static int
WalSndLoop(void)
{
    char	   *output_message;
    bool		caughtup = false;

    /*
     * Allocate buffer that will be used for each output message.  We do this
     * just once to reduce palloc overhead.  The buffer must be made large
     * enough for maximum-sized messages.
     */
    output_message = palloc(1 + sizeof(WalDataMessageHeader) + MAX_SEND_SIZE);

    /*
     * Allocate buffer that will be used for processing reply messages.  As
     * above, do this just once to reduce palloc overhead.
     */
    initStringInfo(&reply_message);

    /* Initialize the last reply timestamp */
    last_reply_timestamp = GetCurrentTimestamp();

    /* Loop forever, unless we get an error */
    for (;;)
    {
        /*
         * Emergency bailout if postmaster has died.  This is to avoid the
         * necessity for manual cleanup of all postmaster children.
         */
        if (!PostmasterIsAlive(true))
            exit(1);

        /* Process any requests or signals received recently */
        if (got_SIGHUP)
        {
            got_SIGHUP = false;
            ProcessConfigFile(PGC_SIGHUP);
            SyncRepInitConfig();
        }

        /* Normal exit from the walsender is here */
        if (walsender_shutdown_requested)
        {
            /* Inform the standby that XLOG streaming was done */
            pq_puttextmessage('C', "COPY 0");
            pq_flush();

            proc_exit(0);
        }

        /*
         * If we don't have any pending data in the output buffer, try to send
         * some more.
         */
        if (!pq_is_send_pending())
        {
            XLogSend(output_message, &caughtup);

            /*
             * Even if we wrote all the WAL that was available when we started
             * sending, more might have arrived while we were sending this
             * batch. We had the latch set while sending, so we have not
             * received any signals from that time. Let's arm the latch again,
             * and after that check that we're still up-to-date.
             */
            if (caughtup && !pq_is_send_pending())
            {
                ResetLatch(&MyWalSnd->latch);

                XLogSend(output_message, &caughtup);
            }
        }

        /* Flush pending output to the client */
        if (pq_flush_if_writable() != 0)
            break;

        /*
         * When SIGUSR2 arrives, we send any outstanding logs up to the
         * shutdown checkpoint record (i.e., the latest record) and exit.
         */
        if (walsender_ready_to_stop && !pq_is_send_pending())
        {
            XLogSend(output_message, &caughtup);
            ProcessRepliesIfAny();
            if (caughtup && !pq_is_send_pending())
                walsender_shutdown_requested = true;
        }

        if ((caughtup || pq_is_send_pending()) &&
                !got_SIGHUP &&
                !walsender_shutdown_requested)
        {
            TimestampTz finish_time = 0;
            long		sleeptime;

            /* Reschedule replication timeout */
            if (replication_timeout > 0)
            {
                long		secs;
                int			usecs;

                finish_time = TimestampTzPlusMilliseconds(last_reply_timestamp,
                              replication_timeout);
                TimestampDifference(GetCurrentTimestamp(),
                                    finish_time, &secs, &usecs);
                sleeptime = secs * 1000 + usecs / 1000;
                if (WalSndDelay < sleeptime)
                    sleeptime = WalSndDelay;
            }
            else
            {
                /*
                 * XXX: Without timeout, we don't really need the periodic
                 * wakeups anymore, WaitLatchOrSocket should reliably wake up
                 * as soon as something interesting happens.
                 */
                sleeptime = WalSndDelay;
            }

            /* Sleep */
            WaitLatchOrSocket(&MyWalSnd->latch, MyProcPort->sock,
                              true, pq_is_send_pending(),
                              sleeptime);

            /* Check for replication timeout */
            if (replication_timeout > 0 &&
                    GetCurrentTimestamp() >= finish_time)
            {
                /*
                 * Since typically expiration of replication timeout means
                 * communication problem, we don't send the error message to
                 * the standby.
                 */
                ereport(COMMERROR,
                        (errmsg("terminating walsender process due to replication timeout")));
                break;
            }
        }

        /*
         * If we're in catchup state, see if its time to move to streaming.
         * This is an important state change for users, since before this
         * point data loss might occur if the primary dies and we need to
         * failover to the standby. The state change is also important for
         * synchronous replication, since commits that started to wait at that
         * point might wait for some time.
         */
        if (MyWalSnd->state == WALSNDSTATE_CATCHUP && caughtup)
        {
            ereport(DEBUG1,
                    (errmsg("standby \"%s\" has now caught up with primary",
                            application_name)));
            WalSndSetState(WALSNDSTATE_STREAMING);
        }

        ProcessRepliesIfAny();
    }

    /*
     * Get here on send failure.  Clean up and exit.
     *
     * Reset whereToSendOutput to prevent ereport from attempting to send any
     * more messages to the standby.
     */
    if (whereToSendOutput == DestRemote)
        whereToSendOutput = DestNone;

    proc_exit(0);
    return 1;					/* keep the compiler quiet */
}