/* Main entry point for walsender process */
int
WalSenderMain(void)
{
MemoryContext walsnd_context;
am_cascading_walsender = RecoveryInProgress();
/* Create a per-walsender data structure in shared memory */
InitWalSnd();
/*
* Create a memory context that we will do all our work in. We do this so
* that we can reset the context during error recovery and thereby avoid
* possible memory leaks. Formerly this code just ran in
* TopMemoryContext, but resetting that would be a really bad idea.
*
* XXX: we don't actually attempt error recovery in walsender, we just
* close the connection and exit.
*/
walsnd_context = AllocSetContextCreate(TopMemoryContext,
"Wal Sender",
ALLOCSET_DEFAULT_MINSIZE,
ALLOCSET_DEFAULT_INITSIZE,
ALLOCSET_DEFAULT_MAXSIZE);
MemoryContextSwitchTo(walsnd_context);
/* Set up resource owner */
CurrentResourceOwner = ResourceOwnerCreate(NULL, "walsender top-level resource owner");
/* Unblock signals (they were blocked when the postmaster forked us) */
PG_SETMASK(&UnBlockSig);
/*
* Use the recovery target timeline ID during recovery
*/
if (am_cascading_walsender)
ThisTimeLineID = GetRecoveryTargetTLI();
/* Tell the standby that walsender is ready for receiving commands */
ReadyForQuery(DestRemote);
/* Handle handshake messages before streaming */
WalSndHandshake();
/* Initialize shared memory status */
{
/* use volatile pointer to prevent code rearrangement */
volatile WalSnd *walsnd = MyWalSnd;
SpinLockAcquire(&walsnd->mutex);
walsnd->sentPtr = sentPtr;
SpinLockRelease(&walsnd->mutex);
}
SyncRepInitConfig();
/* Main loop of walsender */
return WalSndLoop();
}
/* 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 */
}
/* 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 */
}
