On Tue, Jan 19, 2021 at 8:34 AM Dilip Kumar <dilipbal...@gmail.com> wrote:
>
> On Tue, 19 Jan 2021 at 8:12 AM, Yugo NAGATA <nag...@sraoss.co.jp> wrote:
>>
>> On Sun, 17 Jan 2021 11:33:52 +0530
>> Dilip Kumar <dilipbal...@gmail.com> wrote:
>>
>> > On Thu, Jan 14, 2021 at 6:49 PM Yugo NAGATA <nag...@sraoss.co.jp> wrote:
>> > >
>> > > On Wed, 13 Jan 2021 17:49:43 +0530
>> > > Dilip Kumar <dilipbal...@gmail.com> wrote:
>> > >
>> > > > On Wed, Jan 13, 2021 at 3:35 PM Dilip Kumar <dilipbal...@gmail.com>
>> > > > wrote:
>> > > > >
>> > > > > On Wed, Jan 13, 2021 at 3:27 PM Yugo NAGATA <nag...@sraoss.co.jp>
>> > > > > wrote:
>> > > > > >
>> > > > > > On Thu, 10 Dec 2020 11:25:23 +0530
>> > > > > > Dilip Kumar <dilipbal...@gmail.com> wrote:
>> > > > > >
>> > > > > > > > > However, I wonder users don't expect pg_is_wal_replay_paused
>> > > > > > > > > to wait.
>> > > > > > > > > Especially, if max_standby_streaming_delay is -1, this will
>> > > > > > > > > be blocked forever,
>> > > > > > > > > although this setting may not be usual. In addition, some
>> > > > > > > > > users may set
>> > > > > > > > > recovery_min_apply_delay for a large. If such users call
>> > > > > > > > > pg_is_wal_replay_paused,
>> > > > > > > > > it could wait for a long time.
>> > > > > > > > >
>> > > > > > > > > At least, I think we need some descriptions on document to
>> > > > > > > > > explain
>> > > > > > > > > pg_is_wal_replay_paused could wait while a time.
>> > > > > > > >
>> > > > > > > > Ok
>> > > > > > >
>> > > > > > > Fixed this, added some comments in .sgml as well as in function
>> > > > > > > header
>> > > > > >
>> > > > > > Thank you for fixing this.
>> > > > > >
>> > > > > > Also, is it better to fix the description of pg_wal_replay_pause
>> > > > > > from
>> > > > > > "Pauses recovery." to "Request to pause recovery." in according
>> > > > > > with
>> > > > > > pg_is_wal_replay_paused?
>> > > > >
>> > > > > Okay
>> > > > >
>> > > > > >
>> > > > > > > > > Also, how about adding a new boolean argument to
>> > > > > > > > > pg_is_wal_replay_paused to
>> > > > > > > > > control whether this waits for recovery to get paused or
>> > > > > > > > > not? By setting its
>> > > > > > > > > default value to true or false, users can use the old format
>> > > > > > > > > for calling this
>> > > > > > > > > and the backward compatibility can be maintained.
>> > > > > > > >
>> > > > > > > > So basically, if the wait_recovery_pause flag is false then we
>> > > > > > > > will
>> > > > > > > > immediately return true if the pause is requested? I agree
>> > > > > > > > that it is
>> > > > > > > > good to have an API to know whether the recovery pause is
>> > > > > > > > requested or
>> > > > > > > > not but I am not sure is it good idea to make this API serve
>> > > > > > > > both the
>> > > > > > > > purpose? Anyone else have any thoughts on this?
>> > > > > > > >
>> > > > > >
>> > > > > > I think the current pg_is_wal_replay_paused() already has another
>> > > > > > purpose;
>> > > > > > this waits recovery to actually get paused. If we want to limit
>> > > > > > this API's
>> > > > > > purpose only to return the pause state, it seems better to fix
>> > > > > > this to return
>> > > > > > the actual state at the cost of lacking the backward
>> > > > > > compatibility. If we want
>> > > > > > to know whether pause is requested, we may add a new API like
>> > > > > > pg_is_wal_replay_paluse_requeseted(). Also, if we want to wait
>> > > > > > recovery to actually
>> > > > > > get paused, we may add an option to pg_wal_replay_pause() for this
>> > > > > > purpose.
>> > > > > >
>> > > > > > However, this might be a bikeshedding. If anyone don't care that
>> > > > > > pg_is_wal_replay_paused() can make user wait for a long time, I
>> > > > > > don't care either.
>> > > > >
>> > > > > I don't think that it will be blocked ever, because
>> > > > > pg_wal_replay_pause is sending the WakeupRecovery() which means the
>> > > > > recovery process will not be stuck on waiting for the WAL.
>> > >
>> > > Yes, there is no stuck on waiting for the WAL. However, it can be stuck
>> > > during resolving
>> > > a recovery conflict. The process could wait for
>> > > max_standby_streaming_delay or
>> > > max_standby_archive_delay at most before recovery get completely paused.
>> >
>> > Okay, I agree that it is possible so for handling this we have a
>> > couple of options
>> > 1. pg_is_wal_replay_paused(), interface will wait for recovery to
>> > actually get paused, but user have an option to cancel that. So I
>> > agree that there is currently no option to just know that recovery
>> > pause is requested without waiting for its actually get paused if it
>> > is requested. So one option is we can provide an another interface as
>> > you mentioned pg_is_wal_replay_paluse_requeseted(), which can just
>> > return the request status. I am not sure how useful it is.
>>
>> If it is acceptable that pg_is_wal_replay_paused() makes users wait,
>> I'm ok for the current interface. I don't feel the need of
>> pg_is_wal_replay_paluse_requeseted().
>>
>> >
>> > 2. Pass an option to pg_is_wal_replay_paused whether to wait for
>> > recovery to actually get paused or not.
>> >
>> > 3. Pass an option to pg_wal_replay_pause(), whether to wait for
>> > recovery pause or just request and return.
>> >
>> > I like the option 1, any other opinion on this?
>> >
>> > > Also, it could wait for recovery_min_apply_delay if it has a valid
>> > > value. It is possible
>> > > that a user set this parameter to a large value, so it could wait for a
>> > > long time. However,
>> > > this will be avoided by calling recoveryPausesHere() or
>> > > CheckAndSetRecoveryPause() in
>> > > recoveryApplyDelay().
>> >
>> > Right
>>
>> Is there any reason not to do it?
>
>
>
> I think I missed that.. I will do in the next version
>
In the last patch there were some local changes which I did not add to
the patch and it was giving compilation warning so fixed that along
with that I have addressed your this comment as well.
--
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com
From 0dd5d5eb1e17b9c4319dbe5ea1cfb621929efafc Mon Sep 17 00:00:00 2001
From: Dilip Kumar <dilipkumar@localhost.localdomain>
Date: Thu, 10 Dec 2020 11:22:08 +0530
Subject: [PATCH v5] pg_is_wal_replay_paused will wait for recovery to pause
Currently, pg_is_wal_replay_paused, just check whether the recovery
pause is requested or not but it doesn't actually wait for recovery
to get paused. With this patch if recovery pause is not requested
the api will return false otherwise it will wait for recovery to get
paused.
---
doc/src/sgml/func.sgml | 13 +++---
src/backend/access/transam/xlog.c | 73 +++++++++++++++++++++++++++-------
src/backend/access/transam/xlogfuncs.c | 42 +++++++++++++++++--
src/include/access/xlog.h | 11 ++++-
4 files changed, 114 insertions(+), 25 deletions(-)
diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index fd0370a..c51a1d8 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -25180,7 +25180,10 @@ postgres=# SELECT * FROM pg_walfile_name_offset(pg_stop_backup());
<returnvalue>boolean</returnvalue>
</para>
<para>
- Returns true if recovery is paused.
+ If replay pause is requested using <function>pg_wal_replay_pause</function>
+ then this will wait for recovery to actually get paused and once
+ recovery is paused it will return true. Return false if replay pause
+ is not requested.
</para></entry>
</row>
@@ -25219,10 +25222,10 @@ postgres=# SELECT * FROM pg_walfile_name_offset(pg_stop_backup());
<returnvalue>void</returnvalue>
</para>
<para>
- Pauses recovery. While recovery is paused, no further database
- changes are applied. If hot standby is active, all new queries will
- see the same consistent snapshot of the database, and no further query
- conflicts will be generated until recovery is resumed.
+ Request to pause recovery. While recovery is paused, no further
+ database changes are applied. If hot standby is active, all new queries
+ will see the same consistent snapshot of the database, and no further
+ query conflicts will be generated until recovery is resumed.
</para>
<para>
This function is restricted to superusers by default, but other users
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 199d911..d6438a3 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -725,8 +725,8 @@ typedef struct XLogCtlData
* only relevant for replication or archive recovery
*/
TimestampTz currentChunkStartTime;
- /* Are we requested to pause recovery? */
- bool recoveryPause;
+ /* Recovery pause state */
+ RecoveryPauseState recoveryPauseState;
/*
* lastFpwDisableRecPtr points to the start of the last replayed
@@ -898,7 +898,9 @@ static void validateRecoveryParameters(void);
static void exitArchiveRecovery(TimeLineID endTLI, XLogRecPtr endOfLog);
static bool recoveryStopsBefore(XLogReaderState *record);
static bool recoveryStopsAfter(XLogReaderState *record);
+static void CheckAndSetRecoveryPause(void);
static void recoveryPausesHere(bool endOfRecovery);
+static RecoveryPauseState GetRecoveryPauseState(void);
static bool recoveryApplyDelay(XLogReaderState *record);
static void SetLatestXTime(TimestampTz xtime);
static void SetCurrentChunkStartTime(TimestampTz xtime);
@@ -6022,8 +6024,18 @@ recoveryStopsAfter(XLogReaderState *record)
return false;
}
+static void
+CheckAndSetRecoveryPause(void)
+{
+ /* If recovery pause is requested then set it paused */
+ SpinLockAcquire(&XLogCtl->info_lck);
+ if (XLogCtl->recoveryPauseState == RECOVERY_PAUSE_REQUESTED)
+ XLogCtl->recoveryPauseState = RECOVERY_PAUSED;
+ SpinLockRelease(&XLogCtl->info_lck);
+}
+
/*
- * Wait until shared recoveryPause flag is cleared.
+ * Wait until shared recoveryPause is set to RECOVERY_IN_PROGRESS.
*
* endOfRecovery is true if the recovery target is reached and
* the paused state starts at the end of recovery because of
@@ -6053,34 +6065,54 @@ recoveryPausesHere(bool endOfRecovery)
(errmsg("recovery has paused"),
errhint("Execute pg_wal_replay_resume() to continue.")));
- while (RecoveryIsPaused())
+ while (RecoveryPauseRequested())
{
+
HandleStartupProcInterrupts();
+
if (CheckForStandbyTrigger())
return;
pgstat_report_wait_start(WAIT_EVENT_RECOVERY_PAUSE);
+
+ /*
+ * While we are in the loop, user might resume and pause again so set
+ * this everytime.
+ */
+ CheckAndSetRecoveryPause();
pg_usleep(1000000L); /* 1000 ms */
pgstat_report_wait_end();
}
}
-bool
-RecoveryIsPaused(void)
+static RecoveryPauseState
+GetRecoveryPauseState(void)
{
- bool recoveryPause;
+ RecoveryPauseState recoveryPauseState;
SpinLockAcquire(&XLogCtl->info_lck);
- recoveryPause = XLogCtl->recoveryPause;
+ recoveryPauseState = XLogCtl->recoveryPauseState;
SpinLockRelease(&XLogCtl->info_lck);
- return recoveryPause;
+ return recoveryPauseState;
+}
+
+bool
+RecoveryIsPaused(void)
+{
+ return (GetRecoveryPauseState() == RECOVERY_PAUSED) ? true : false;
+}
+
+bool
+RecoveryPauseRequested(void)
+{
+ return (GetRecoveryPauseState() != RECOVERY_IN_PROGRESS) ? true : false;
}
void
-SetRecoveryPause(bool recoveryPause)
+SetRecoveryPause(RecoveryPauseState recoveryPause)
{
SpinLockAcquire(&XLogCtl->info_lck);
- XLogCtl->recoveryPause = recoveryPause;
+ XLogCtl->recoveryPauseState = recoveryPause;
SpinLockRelease(&XLogCtl->info_lck);
}
@@ -6172,6 +6204,10 @@ recoveryApplyDelay(XLogReaderState *record)
WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
msecs,
WAIT_EVENT_RECOVERY_APPLY_DELAY);
+
+ /* test for recovery pause if user has requested the pause */
+ if (((volatile XLogCtlData *) XLogCtl)->recoveryPauseState)
+ recoveryPausesHere(false);
}
return true;
}
@@ -7143,7 +7179,7 @@ StartupXLOG(void)
XLogCtl->lastReplayedTLI = XLogCtl->replayEndTLI;
XLogCtl->recoveryLastXTime = 0;
XLogCtl->currentChunkStartTime = 0;
- XLogCtl->recoveryPause = false;
+ XLogCtl->recoveryPauseState = RECOVERY_IN_PROGRESS;
SpinLockRelease(&XLogCtl->info_lck);
/* Also ensure XLogReceiptTime has a sane value */
@@ -7247,7 +7283,8 @@ StartupXLOG(void)
* otherwise would is a minor issue, so it doesn't seem worth
* adding another spinlock cycle to prevent that.
*/
- if (((volatile XLogCtlData *) XLogCtl)->recoveryPause)
+ if (((volatile XLogCtlData *) XLogCtl)->recoveryPauseState
+ != RECOVERY_IN_PROGRESS)
recoveryPausesHere(false);
/*
@@ -7272,7 +7309,7 @@ StartupXLOG(void)
* here otherwise pausing during the delay-wait wouldn't
* work.
*/
- if (((volatile XLogCtlData *) XLogCtl)->recoveryPause)
+ if (((volatile XLogCtlData *) XLogCtl)->recoveryPauseState)
recoveryPausesHere(false);
}
@@ -7446,7 +7483,7 @@ StartupXLOG(void)
proc_exit(3);
case RECOVERY_TARGET_ACTION_PAUSE:
- SetRecoveryPause(true);
+ SetRecoveryPause(RECOVERY_PAUSE_REQUESTED);
recoveryPausesHere(true);
/* drop into promote */
@@ -12599,6 +12636,12 @@ WaitForWALToBecomeAvailable(XLogRecPtr RecPtr, bool randAccess,
elog(ERROR, "unexpected WAL source %d", currentSource);
}
+ /* test for recovery pause if user has requested the pause */
+ if (((volatile XLogCtlData *) XLogCtl)->recoveryPauseState)
+ recoveryPausesHere(false);
+
+ now = GetCurrentTimestamp();
+
/*
* This possibly-long loop needs to handle interrupts of startup
* process.
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 5e1aab3..5847bd3 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -517,7 +517,7 @@ pg_walfile_name(PG_FUNCTION_ARGS)
}
/*
- * pg_wal_replay_pause - pause recovery now
+ * pg_wal_replay_pause - Request to pause recovery
*
* Permission checking for this function is managed through the normal
* GRANT system.
@@ -538,7 +538,10 @@ pg_wal_replay_pause(PG_FUNCTION_ARGS)
errhint("%s cannot be executed after promotion is triggered.",
"pg_wal_replay_pause()")));
- SetRecoveryPause(true);
+ SetRecoveryPause(RECOVERY_PAUSE_REQUESTED);
+
+ /* wake up the recovery process so that it can process the pause request */
+ WakeupRecovery();
PG_RETURN_VOID();
}
@@ -565,13 +568,17 @@ pg_wal_replay_resume(PG_FUNCTION_ARGS)
errhint("%s cannot be executed after promotion is triggered.",
"pg_wal_replay_resume()")));
- SetRecoveryPause(false);
+ SetRecoveryPause(RECOVERY_IN_PROGRESS);
PG_RETURN_VOID();
}
/*
* pg_is_wal_replay_paused
+ *
+ * If replay pause is requested using pg_wal_replay_pause then this will wait
+ * for recovery to actually get paused and once recovery is paused it will
+ * return true. Return false if replay pause is not requested.
*/
Datum
pg_is_wal_replay_paused(PG_FUNCTION_ARGS)
@@ -582,7 +589,34 @@ pg_is_wal_replay_paused(PG_FUNCTION_ARGS)
errmsg("recovery is not in progress"),
errhint("Recovery control functions can only be executed during recovery.")));
- PG_RETURN_BOOL(RecoveryIsPaused());
+ /* loop until the recovery is actually paused */
+ for (;;)
+ {
+ /* If recovery pause is not requested then return false */
+ if (!RecoveryPauseRequested())
+ PG_RETURN_BOOL(false);
+
+ if (RecoveryIsPaused())
+ PG_RETURN_BOOL(true);
+
+ /* wait for 10 msec */
+ pg_usleep(10000L);
+
+ CHECK_FOR_INTERRUPTS();
+
+ /*
+ * If recovery is not in progress anymore then report an error this
+ * could happen if the standby is promoted while we were waiting for
+ * recovery to get paused.
+ */
+ if (!RecoveryInProgress())
+ ereport(ERROR,
+ (errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+ errmsg("recovery is not in progress"),
+ errhint("The standby was promoted while waiting for recovery to be paused.")));
+ }
+
+ PG_RETURN_BOOL(true);
}
/*
diff --git a/src/include/access/xlog.h b/src/include/access/xlog.h
index 75ec107..d00df1b 100644
--- a/src/include/access/xlog.h
+++ b/src/include/access/xlog.h
@@ -174,6 +174,14 @@ typedef enum RecoveryState
RECOVERY_STATE_DONE /* currently in production */
} RecoveryState;
+/* Recovery pause states */
+typedef enum RecoveryPauseState
+{
+ RECOVERY_IN_PROGRESS = 0,
+ RECOVERY_PAUSE_REQUESTED,
+ RECOVERY_PAUSED,
+} RecoveryPauseState;
+
extern PGDLLIMPORT int wal_level;
/* Is WAL archiving enabled (always or only while server is running normally)? */
@@ -311,7 +319,8 @@ extern XLogRecPtr GetXLogReplayRecPtr(TimeLineID *replayTLI);
extern XLogRecPtr GetXLogInsertRecPtr(void);
extern XLogRecPtr GetXLogWriteRecPtr(void);
extern bool RecoveryIsPaused(void);
-extern void SetRecoveryPause(bool recoveryPause);
+extern bool RecoveryPauseRequested(void);
+extern void SetRecoveryPause(RecoveryPauseState recoveryPause);
extern TimestampTz GetLatestXTime(void);
extern TimestampTz GetCurrentChunkReplayStartTime(void);
--
1.8.3.1
