Re: [HACKERS] Bug: walsender and high CPU usage
On 12.03.2012 15:30, Fujii Masao wrote: On Mon, Mar 12, 2012 at 10:27 PM, Fujii Masaomasao.fu...@gmail.com wrote: On Mon, Mar 12, 2012 at 7:58 PM, Heikki Linnakangas heikki.linnakan...@enterprisedb.com wrote: I also think we should backport commit cff75130b5f63e45423c2ed90d6f2e84c21ef840, except for the removal of wal_sender_delay). Agreed. The attached patch is the same as cff75130b5f63e45423c2ed90d6f2e84c21ef840, except for the removal of wal_sender_delay. Could you apply this? Oh, I forgot to attach the patch. Patch attached really. Thanks, committed. -- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
Re: [HACKERS] Bug: walsender and high CPU usage
On 09.03.2012 13:40, Fujii Masao wrote:
I found the bug which causes walsender to enter into busy loop
when replication connection is terminated. Walsender consumes
lots of CPU resource (%sys), and this situation lasts until it has
detected the termination of replication connection and exited.
The cause of this bug is that the walsender loop doesn't call
ResetLatch at all in the above case. Since the latch remains set,
the walsender loop cannot sleep on the latch, i.e., WaitLatch
always returns immediately.
We can fix this bug by adding ResetLatch into the top of the
walsender loop. Patch attached.
This bug exists in 9.1 but not in 9.2dev. In 9.2dev, this bug has
already been fixed by the commit
(cff75130b5f63e45423c2ed90d6f2e84c21ef840). This commit
refactors and refines the walsender loop logic in addition to
adding ResetLatch. So I'm tempted to backport this commit
(except the deletion of wal_sender_delay) to 9.1 rather than
applying the attached patch. OTOH, attached patch is quite simple,
and its impact on 9.1 would be very small, so it's easy to backport that.
Thought?
This patch makes the code that follows bogus:
/*
* 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);
}
}
The comment is no longer valid, and the calls to ResetLatch and XLogSend
are no longer necessary, once you have the ResetLatch() call at the top
of the loop.
I also think we should backport commit
cff75130b5f63e45423c2ed90d6f2e84c21ef840, except for the removal of
wal_sender_delay).
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
--
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Re: [HACKERS] Bug: walsender and high CPU usage
On Mon, Mar 12, 2012 at 7:58 PM, Heikki Linnakangas
heikki.linnakan...@enterprisedb.com wrote:
On 09.03.2012 13:40, Fujii Masao wrote:
I found the bug which causes walsender to enter into busy loop
when replication connection is terminated. Walsender consumes
lots of CPU resource (%sys), and this situation lasts until it has
detected the termination of replication connection and exited.
The cause of this bug is that the walsender loop doesn't call
ResetLatch at all in the above case. Since the latch remains set,
the walsender loop cannot sleep on the latch, i.e., WaitLatch
always returns immediately.
We can fix this bug by adding ResetLatch into the top of the
walsender loop. Patch attached.
This bug exists in 9.1 but not in 9.2dev. In 9.2dev, this bug has
already been fixed by the commit
(cff75130b5f63e45423c2ed90d6f2e84c21ef840). This commit
refactors and refines the walsender loop logic in addition to
adding ResetLatch. So I'm tempted to backport this commit
(except the deletion of wal_sender_delay) to 9.1 rather than
applying the attached patch. OTOH, attached patch is quite simple,
and its impact on 9.1 would be very small, so it's easy to backport that.
Thought?
This patch makes the code that follows bogus:
/*
* 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);
}
}
The comment is no longer valid, and the calls to ResetLatch and XLogSend are
no longer necessary, once you have the ResetLatch() call at the top of the
loop.
Right.
I also think we should backport commit
cff75130b5f63e45423c2ed90d6f2e84c21ef840, except for the removal of
wal_sender_delay).
Agreed. The attached patch is the same as
cff75130b5f63e45423c2ed90d6f2e84c21ef840,
except for the removal of wal_sender_delay. Could you apply this?
Regards,
--
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center
--
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Re: [HACKERS] Bug: walsender and high CPU usage
On Mon, Mar 12, 2012 at 10:27 PM, Fujii Masao masao.fu...@gmail.com wrote:
On Mon, Mar 12, 2012 at 7:58 PM, Heikki Linnakangas
heikki.linnakan...@enterprisedb.com wrote:
On 09.03.2012 13:40, Fujii Masao wrote:
I found the bug which causes walsender to enter into busy loop
when replication connection is terminated. Walsender consumes
lots of CPU resource (%sys), and this situation lasts until it has
detected the termination of replication connection and exited.
The cause of this bug is that the walsender loop doesn't call
ResetLatch at all in the above case. Since the latch remains set,
the walsender loop cannot sleep on the latch, i.e., WaitLatch
always returns immediately.
We can fix this bug by adding ResetLatch into the top of the
walsender loop. Patch attached.
This bug exists in 9.1 but not in 9.2dev. In 9.2dev, this bug has
already been fixed by the commit
(cff75130b5f63e45423c2ed90d6f2e84c21ef840). This commit
refactors and refines the walsender loop logic in addition to
adding ResetLatch. So I'm tempted to backport this commit
(except the deletion of wal_sender_delay) to 9.1 rather than
applying the attached patch. OTOH, attached patch is quite simple,
and its impact on 9.1 would be very small, so it's easy to backport that.
Thought?
This patch makes the code that follows bogus:
/*
* 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);
}
}
The comment is no longer valid, and the calls to ResetLatch and XLogSend are
no longer necessary, once you have the ResetLatch() call at the top of the
loop.
Right.
I also think we should backport commit
cff75130b5f63e45423c2ed90d6f2e84c21ef840, except for the removal of
wal_sender_delay).
Agreed. The attached patch is the same as
cff75130b5f63e45423c2ed90d6f2e84c21ef840,
except for the removal of wal_sender_delay. Could you apply this?
Oh, I forgot to attach the patch. Patch attached really.
Regards,
--
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center
*** a/src/backend/replication/walsender.c
--- b/src/backend/replication/walsender.c
***
*** 476,482 ProcessRepliesIfAny(void)
{
unsigned char firstchar;
int r;
! int received = false;
for (;;)
{
--- 476,482
{
unsigned char firstchar;
int r;
! bool received = false;
for (;;)
{
***
*** 700,705 WalSndLoop(void)
--- 700,708
/* 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.
***
*** 718,777 WalSndLoop(void)
/* 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,
[HACKERS] Bug: walsender and high CPU usage
Hi,
I found the bug which causes walsender to enter into busy loop
when replication connection is terminated. Walsender consumes
lots of CPU resource (%sys), and this situation lasts until it has
detected the termination of replication connection and exited.
The cause of this bug is that the walsender loop doesn't call
ResetLatch at all in the above case. Since the latch remains set,
the walsender loop cannot sleep on the latch, i.e., WaitLatch
always returns immediately.
We can fix this bug by adding ResetLatch into the top of the
walsender loop. Patch attached.
This bug exists in 9.1 but not in 9.2dev. In 9.2dev, this bug has
already been fixed by the commit
(cff75130b5f63e45423c2ed90d6f2e84c21ef840). This commit
refactors and refines the walsender loop logic in addition to
adding ResetLatch. So I'm tempted to backport this commit
(except the deletion of wal_sender_delay) to 9.1 rather than
applying the attached patch. OTOH, attached patch is quite simple,
and its impact on 9.1 would be very small, so it's easy to backport that.
Thought?
Regards,
--
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 3497269..35c7042 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -700,6 +700,9 @@ WalSndLoop(void)
/* 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.
--
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