On Fri, Dec 25, 2015 at 7:21 AM, Thomas Munro
<[email protected]> wrote:
> On Fri, Dec 25, 2015 at 8:50 AM, Masahiko Sawada <[email protected]>
> wrote:
>> On Wed, Dec 23, 2015 at 8:45 AM, Thomas Munro
>> <[email protected]> wrote:
>>> On Wed, Dec 23, 2015 at 3:50 PM, Thomas Munro
>>> <[email protected]> wrote:
>>>> If you got rid of SyncRepGetSyncStandbysOnePriority as suggested
>>>> above, then this function could be renamed to SyncRepGetSyncStandbys.
>>>> I think it would be a tiny bit nicer if it also took a Size n argument
>>>> along with the output buffer pointer.
>>
>> Sorry, I could not get your point. SyncRepGetSyncStandbysPriority()
>> function uses synchronous_standby_num which is global variable.
>> But you mean that the number of synchronous standbys is given as
>> function argument?
>
> Yeah, I was thinking of it as the output buffer size which I would be
> inclined to make more explicit (I am still coming to terms with the
> use of global variables in Postgres) but it doesn't matter, please
> disregard that suggestion.
>
>>>> As for the body of that function (which I won't paste here), it
>>>> contains an algorithm to find the top K elements in an array of N
>>>> elements. It does that with a linear search through the top K seen so
>>>> far for each value in the input array, so its worst case is O(KN)
>>>> comparisons. Some of the sorting gurus on this list might have
>>>> something to say about that but my take is that it seems fine for the
>>>> tiny values of K and N that we're dealing with here, and it's nice
>>>> that it doesn't need any space other than the output buffer, unlike
>>>> some other top-K algorithms which would win for larger inputs.
>>
>> Yeah, it's improvement point.
>> But I'm assumed that the number of synchronous replication is not
>> large, so I use this algorithm as first version.
>> And I think that its worst case is O(K(N-K)). Am I missing something?
>
> You're right, I was dropping that detail, in the tradition of the
> hand-wavy school of big-O notation. (I suppose you could skip the
> inner loop when the priority is lower than the current lowest
> priority, giving a O(N) best case when the walsenders are perfectly
> ordered by coincidence. Probably a bad idea or just not worth
> worrying about.)
Thank you for reviewing the patch.
Yeah, I added the logic that skip the inner loop.
>
>> Attached latest version patch.
>
> +/*
> + * Obtain currently synced LSN location: write and flush, using priority
> - * In 9.1 we support only a single synchronous standby, chosen from a
> - * priority list of synchronous_standby_names. Before it can become the
> + * In 9.6 we support multiple synchronous standby, chosen from a priority
>
> s/standby/standbys/
>
> + * list of synchronous_standby_names. Before it can become the
>
> s/Before it can become the/Before any standby can become a/
>
> * synchronous standby it must have caught up with the primary; that may
> * take some time. Once caught up, the current highest priority standby
>
> s/standby/standbys/
>
> * will release waiters from the queue.
>
> +bool
> +SyncRepGetSyncLsnsPriority(XLogRecPtr *write_pos, XLogRecPtr *flush_pos)
> +{
> + int sync_standbys[synchronous_standby_num];
>
> I think this should be sync_standbys[SYNC_REP_MAX_SYNC_STANDBY_NUM].
> (Variable sized arrays are a feature of C99 and PostgreSQL is written
> in C89.)
>
> +/*
> + * Populate a caller-supplied array which much have enough space for
> + * synchronous_standby_num. Returns position of standbys currently
> + * considered as synchronous, and its length.
> + */
> +int
> +SyncRepGetSyncStandbys(int *sync_standbys)
>
> s/much/must/ (my bad, in previous email).
>
> + ereport(ERROR,
> + (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
> + errmsg("The number of synchronous standbys must be smaller than the
> number of listed : %d",
> + synchronous_standby_num)));
>
> How about "the number of synchronous standbys exceeds the length of
> the standby list: %d"? Error messages usually start with lower case,
> ':' is not usually preceded by a space.
>
> + ereport(ERROR,
> + (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
> + errmsg("The number of synchronous standbys must be between 1 and %d : %d",
>
> s/The/the/, s/ : /: /
Fixed you mentioned.
Attached latest v5 patch.
Please review it.
Regards,
--
Masahiko Sawada
diff --git a/src/backend/replication/syncrep.c b/src/backend/replication/syncrep.c
index 7f85b88..0c78919 100644
--- a/src/backend/replication/syncrep.c
+++ b/src/backend/replication/syncrep.c
@@ -29,10 +29,10 @@
* single ordered queue of waiting backends, so that we can avoid
* searching the through all waiters each time we receive a reply.
*
- * In 9.1 we support only a single synchronous standby, chosen from a
- * priority list of synchronous_standby_names. Before it can become the
- * synchronous standby it must have caught up with the primary; that may
- * take some time. Once caught up, the current highest priority standby
+ * In 9.6 we support multiple synchronous standbys, chosen from a priority
+ * list of synchronous_standby_names. Before any standby can become a
+ * synchronous standbys it must have caught up with the primary; that may
+ * take some time. Once caught up, the current highest priority standbys
* will release waiters from the queue.
*
* Portions Copyright (c) 2010-2016, PostgreSQL Global Development Group
@@ -59,9 +59,15 @@
/* User-settable parameters for sync rep */
char *SyncRepStandbyNames;
+int synchronous_replication_method;
+int synchronous_standby_num;
#define SyncStandbysDefined() \
- (SyncRepStandbyNames != NULL && SyncRepStandbyNames[0] != '\0')
+ (SyncRepStandbyNames != NULL && \
+ SyncRepStandbyNames[0] != '\0' && \
+ synchronous_standby_num > 0)
+
+#define SYNC_REP_MAX_SYNC_STANDBY_NUM 256
static bool announce_next_takeover = true;
@@ -349,57 +355,185 @@ SyncRepInitConfig(void)
}
/*
- * Find the WAL sender servicing the synchronous standby with the lowest
- * priority value, or NULL if no synchronous standby is connected. If there
- * are multiple standbys with the same lowest priority value, the first one
- * found is selected. The caller must hold SyncRepLock.
+ * Is this wal sender managing a standby that is streaming and
+ * listed as a synchronous standby?
*/
-WalSnd *
-SyncRepGetSynchronousStandby(void)
+bool
+SyncRepActiveListedWalSender(int num)
{
- WalSnd *result = NULL;
- int result_priority = 0;
- int i;
+ volatile WalSnd *walsnd = &WalSndCtl->walsnds[num];
+
+ /* Must be active */
+ if (walsnd->pid == 0)
+ return false;
+
+ /* Must be streaming */
+ if (walsnd->state != WALSNDSTATE_STREAMING)
+ return false;
+
+ /* Must be synchronous */
+ if (walsnd->sync_standby_priority == 0)
+ return false;
+
+ /* Must have a valid flush position */
+ if (XLogRecPtrIsInvalid(walsnd->flush))
+ return false;
+
+ return true;
+}
+
+/*
+ * Get both LSNs: write and flush, according to replication method.
+ * And confirm whether we have advanced to LSN or not.
+ */
+bool
+SyncRepSyncedLsnAdvancedTo(XLogRecPtr *write_pos, XLogRecPtr *flush_pos)
+{
+ XLogRecPtr tmp_write_pos;
+ XLogRecPtr tmp_flush_pos;
+ bool ret = false;
+
+ /* '1-priority' and 'priority' method */
+ if (synchronous_replication_method == SYNC_REP_METHOD_1_PRIORITY ||
+ synchronous_replication_method == SYNC_REP_METHOD_PRIORITY)
+ ret = SyncRepGetSyncLsnsPriority(&tmp_write_pos, &tmp_flush_pos);
+
+ /* Have we advanced LSN? */
+ if (ret)
+ {
+ if (MyWalSnd->write >= tmp_write_pos)
+ *write_pos = tmp_write_pos;
+ if (MyWalSnd->flush >= tmp_flush_pos)
+ *flush_pos = tmp_flush_pos;
+
+ return true;
+ }
+
+ return false;
+}
+
+/*
+ * Populate a caller-supplied array which must have enough space for
+ * synchronous_standby_num. Returns position of standbys currently
+ * considered as synchronous, and its length.
+ */
+int
+SyncRepGetSyncStandbys(int *sync_standbys)
+{
+ int num_sync = 0;
+
+
+ /* '1-priority' and 'priority' method */
+ if (synchronous_replication_method == SYNC_REP_METHOD_1_PRIORITY ||
+ synchronous_replication_method == SYNC_REP_METHOD_PRIORITY)
+ num_sync = SyncRepGetSyncStandbysPriority(sync_standbys);
+
+ return num_sync;
+}
+
+/*
+ * Populates a caller-supplied buffer with the walsnds indexes of the
+ * highest priority active synchronous standbys, up to the a limit of
+ * 'synchronous_standby_num'. The order of the results is undefined.
+ * Return the number of results actually written.
+ */
+int
+SyncRepGetSyncStandbysPriority(int *sync_standbys)
+{
+ int priority = 0;
+ int num_sync = 0;
+ int i;
for (i = 0; i < max_wal_senders; i++)
{
/* Use volatile pointer to prevent code rearrangement */
volatile WalSnd *walsnd = &WalSndCtl->walsnds[i];
- int this_priority;
+ int j;
- /* Must be active */
- if (walsnd->pid == 0)
+ /* Is this wal sender considerable one? */
+ if (!SyncRepActiveListedWalSender(i))
continue;
- /* Must be streaming */
- if (walsnd->state != WALSNDSTATE_STREAMING)
- continue;
+ if (num_sync == synchronous_standby_num &&
+ walsnd->sync_standby_priority < priority)
+ {
+ for (j = 0; j < num_sync; j++)
+ {
+ volatile WalSnd *walsndloc = &WalSndCtl->walsnds[sync_standbys[j]];
+
+ /* Found lowest priority standby, so replace it */
+ if (walsndloc->sync_standby_priority == priority &&
+ walsnd->sync_standby_priority < priority)
+ sync_standbys[j] = i;
+
+ /* Update highest priority standby */
+ if (priority < walsndloc->sync_standby_priority)
+ priority = walsndloc->sync_standby_priority;
+ }
+ }
+ else
+ {
+ sync_standbys[num_sync] = i;
+ num_sync++;
- /* Must be synchronous */
- this_priority = walsnd->sync_standby_priority;
- if (this_priority == 0)
- continue;
+ /* Keep track highest priority standby */
+ if (priority < walsnd->sync_standby_priority)
+ priority = walsnd->sync_standby_priority;
+ }
+ }
- /* Must have a lower priority value than any previous ones */
- if (result != NULL && result_priority <= this_priority)
- continue;
+ return num_sync;
+}
- /* Must have a valid flush position */
- if (XLogRecPtrIsInvalid(walsnd->flush))
+/*
+ * Obtain currently synced LSN location: write and flush, using priority
+ * method.
+ */
+bool
+SyncRepGetSyncLsnsPriority(XLogRecPtr *write_pos, XLogRecPtr *flush_pos)
+{
+ int sync_standbys[SYNC_REP_MAX_SYNC_STANDBY_NUM];
+ int num_sync;
+ int i;
+ XLogRecPtr synced_write = InvalidXLogRecPtr;
+ XLogRecPtr synced_flush = InvalidXLogRecPtr;
+
+ num_sync = SyncRepGetSyncStandbysPriority(sync_standbys);
+
+ /* Just return, if sync standby is not enough */
+ if (num_sync < synchronous_standby_num)
+ {
+ return false;
+ }
+
+ for (i = 0; i < num_sync; i++)
+ {
+ volatile WalSnd *walsndloc = &WalSndCtl->walsnds[sync_standbys[i]];
+
+ SpinLockAcquire(&walsndloc->mutex);
+
+ /* Store first candidate */
+ if (XLogRecPtrIsInvalid(synced_write) && XLogRecPtrIsInvalid(synced_flush))
+ {
+ synced_write = walsndloc->write;
+ synced_flush = walsndloc->flush;
+ SpinLockRelease(&walsndloc->mutex);
continue;
+ }
- result = (WalSnd *) walsnd;
- result_priority = this_priority;
+ /* Keep/Collect the earliest write and flush LSNs among prioritized standbys */
+ if (synced_write > walsndloc->write)
+ synced_write = walsndloc->write;
+ if (synced_flush > walsndloc->flush)
+ synced_flush = walsndloc->flush;
- /*
- * If priority is equal to 1, there cannot be any other WAL senders
- * with a lower priority, so we're done.
- */
- if (this_priority == 1)
- return result;
+ SpinLockRelease(&walsndloc->mutex);
}
- return result;
+ *write_pos = synced_write;
+ *flush_pos = synced_flush;
+
+ return true;
}
/*
@@ -413,9 +547,9 @@ void
SyncRepReleaseWaiters(void)
{
volatile WalSndCtlData *walsndctl = WalSndCtl;
- WalSnd *syncWalSnd;
- int numwrite = 0;
- int numflush = 0;
+ XLogRecPtr write_pos = InvalidXLogRecPtr;
+ XLogRecPtr flush_pos = InvalidXLogRecPtr;
+ int numwrite, numflush;
/*
* If this WALSender is serving a standby that is not on the list of
@@ -428,23 +562,12 @@ SyncRepReleaseWaiters(void)
XLogRecPtrIsInvalid(MyWalSnd->flush))
return;
- /*
- * We're a potential sync standby. Release waiters if we are the highest
- * priority standby.
- */
LWLockAcquire(SyncRepLock, LW_EXCLUSIVE);
- syncWalSnd = SyncRepGetSynchronousStandby();
-
- /* We should have found ourselves at least */
- Assert(syncWalSnd != NULL);
- /*
- * If we aren't managing the highest priority standby then just leave.
- */
- if (syncWalSnd != MyWalSnd)
+ /* Get currently synced LSNs according to replication method */
+ if (!(SyncRepSyncedLsnAdvancedTo(&write_pos, &flush_pos)))
{
LWLockRelease(SyncRepLock);
- announce_next_takeover = true;
return;
}
@@ -452,14 +575,14 @@ SyncRepReleaseWaiters(void)
* Set the lsn first so that when we wake backends they will release up to
* this location.
*/
- if (walsndctl->lsn[SYNC_REP_WAIT_WRITE] < MyWalSnd->write)
+ if (walsndctl->lsn[SYNC_REP_WAIT_WRITE] < write_pos)
{
- walsndctl->lsn[SYNC_REP_WAIT_WRITE] = MyWalSnd->write;
+ walsndctl->lsn[SYNC_REP_WAIT_WRITE] = write_pos;
numwrite = SyncRepWakeQueue(false, SYNC_REP_WAIT_WRITE);
}
- if (walsndctl->lsn[SYNC_REP_WAIT_FLUSH] < MyWalSnd->flush)
+ if (walsndctl->lsn[SYNC_REP_WAIT_FLUSH] < flush_pos)
{
- walsndctl->lsn[SYNC_REP_WAIT_FLUSH] = MyWalSnd->flush;
+ walsndctl->lsn[SYNC_REP_WAIT_FLUSH] = flush_pos;
numflush = SyncRepWakeQueue(false, SYNC_REP_WAIT_FLUSH);
}
@@ -498,6 +621,7 @@ SyncRepGetStandbyPriority(void)
ListCell *l;
int priority = 0;
bool found = false;
+ int num = 0;
/*
* Since synchronous cascade replication is not allowed, we always set the
@@ -506,6 +630,10 @@ SyncRepGetStandbyPriority(void)
if (am_cascading_walsender)
return 0;
+ /* If no synchronous standby allowed, no cake for this WAL sender */
+ if (!SyncStandbysDefined())
+ return 0;
+
/* Need a modifiable copy of string */
rawstring = pstrdup(SyncRepStandbyNames);
@@ -521,8 +649,16 @@ SyncRepGetStandbyPriority(void)
foreach(l, elemlist)
{
- char *standby_name = (char *) lfirst(l);
+ char *standby_name;
+
+ if (num == 0 &&
+ synchronous_replication_method != SYNC_REP_METHOD_1_PRIORITY)
+ {
+ num = lfirst_int(l);
+ continue;
+ }
+ standby_name = (char *) lfirst(l);
priority++;
if (pg_strcasecmp(standby_name, application_name) == 0 ||
@@ -683,7 +819,6 @@ SyncRepQueueIsOrderedByLSN(int mode)
* Synchronous Replication functions executed by any process
* ===========================================================
*/
-
bool
check_synchronous_standby_names(char **newval, void **extra, GucSource source)
{
@@ -733,3 +868,42 @@ assign_synchronous_commit(int newval, void *extra)
break;
}
}
+
+void
+ProcessSynchronousReplicationConfig(void)
+{
+ char *rawstring;
+ List *elemlist;
+
+
+ /* Need a modifiable copy of string */
+ rawstring = pstrdup(SyncRepStandbyNames);
+
+ /* Parse string into list of identifiers */
+ SplitIdentifierString(rawstring, ',', &elemlist);
+
+ /* Store them into globl variables */
+ if (synchronous_replication_method == SYNC_REP_METHOD_1_PRIORITY)
+ synchronous_standby_num = 1;
+ else
+ synchronous_standby_num = pg_atoi(lfirst(list_head(elemlist)), sizeof(int), 0);
+
+ /* In 'priority' method, additional validation checks for synchronous_standby_num */
+ if (synchronous_replication_method == SYNC_REP_METHOD_PRIORITY)
+ {
+ if ((list_length(elemlist) - 1) < synchronous_standby_num)
+ ereport(ERROR,
+ (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+ errmsg("the number of synchronous standbys exceed the length of the standby list: %d",
+ synchronous_standby_num)));
+
+ if (1 > synchronous_standby_num ||
+ synchronous_standby_num > SYNC_REP_MAX_SYNC_STANDBY_NUM)
+ ereport(ERROR,
+ (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
+ errmsg("the number of synchronous standbys must be between 1 and %d: %d",
+ SYNC_REP_MAX_SYNC_STANDBY_NUM, synchronous_standby_num)));
+ }
+
+ return;
+}
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index c03e045..8586af4 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -2749,9 +2749,11 @@ pg_stat_get_wal_senders(PG_FUNCTION_ARGS)
Tuplestorestate *tupstore;
MemoryContext per_query_ctx;
MemoryContext oldcontext;
- WalSnd *sync_standby;
+ int *sync_standbys;
+ int num_sync;
int i;
+
/* check to see if caller supports us returning a tuplestore */
if (rsinfo == NULL || !IsA(rsinfo, ReturnSetInfo))
ereport(ERROR,
@@ -2777,11 +2779,13 @@ pg_stat_get_wal_senders(PG_FUNCTION_ARGS)
MemoryContextSwitchTo(oldcontext);
+ sync_standbys = (int *) palloc(sizeof(int) * synchronous_standby_num);
+
/*
- * Get the currently active synchronous standby.
+ * Get the currently active synchronous standbys.
*/
LWLockAcquire(SyncRepLock, LW_SHARED);
- sync_standby = SyncRepGetSynchronousStandby();
+ num_sync = SyncRepGetSyncStandbys(sync_standbys);
LWLockRelease(SyncRepLock);
for (i = 0; i < max_wal_senders; i++)
@@ -2854,18 +2858,34 @@ pg_stat_get_wal_senders(PG_FUNCTION_ARGS)
*/
if (priority == 0)
values[7] = CStringGetTextDatum("async");
- else if (walsnd == sync_standby)
- values[7] = CStringGetTextDatum("sync");
else
- values[7] = CStringGetTextDatum("potential");
+ {
+ int j;
+ bool found = false;
+
+ for (j = 0; j < num_sync; j++)
+ {
+ /* Found sync standby */
+ if (i == sync_standbys[j])
+ {
+ values[7] = CStringGetTextDatum("sync");
+ found = true;
+ break;
+ }
+ }
+ if (!found)
+ values[7] = CStringGetTextDatum("potential");
+ }
}
tuplestore_putvalues(tupstore, tupdesc, values, nulls);
}
/* clean up and return the tuplestore */
+ pfree(sync_standbys);
tuplestore_donestoring(tupstore);
+
return (Datum) 0;
}
diff --git a/src/backend/utils/misc/guc-file.l b/src/backend/utils/misc/guc-file.l
index 48052f9..c2e5812 100644
--- a/src/backend/utils/misc/guc-file.l
+++ b/src/backend/utils/misc/guc-file.l
@@ -18,6 +18,7 @@
#include "miscadmin.h"
#include "storage/fd.h"
#include "utils/guc.h"
+#include "replication/syncrep.h"
/*
@@ -155,6 +156,12 @@ ProcessConfigFile(GucContext context)
*/
(void) ProcessConfigFileInternal(context, true, elevel);
+ /*
+ * After read all synchronous replication configuration parameter, we apply
+ * settings according to replication method.
+ */
+ ProcessSynchronousReplicationConfig();
+
/* Clean up */
MemoryContextSwitchTo(caller_cxt);
MemoryContextDelete(config_cxt);
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 38ba82f..1d6f530 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -310,6 +310,12 @@ static const struct config_enum_entry xmloption_options[] = {
{NULL, 0, false}
};
+static const struct config_enum_entry synchronous_replication_method_options[] = {
+ {"1-priority", SYNC_REP_METHOD_1_PRIORITY, false},
+ {"priority", SYNC_REP_METHOD_PRIORITY, false},
+ {NULL, 0, false}
+};
+
/*
* Although only "on", "off", and "safe_encoding" are documented, we
* accept all the likely variants of "on" and "off".
@@ -3672,6 +3678,16 @@ static struct config_enum ConfigureNamesEnum[] =
NULL, NULL, NULL
},
+ {
+ {"synchronous_replication_method", PGC_SIGHUP, REPLICATION_MASTER,
+ gettext_noop("Method for multiple synchronous replication."),
+ NULL
+ },
+ &synchronous_replication_method,
+ SYNC_REP_METHOD_1_PRIORITY, synchronous_replication_method_options,
+ NULL, NULL, NULL
+ },
+
/* End-of-list marker */
{
{NULL, 0, 0, NULL, NULL}, NULL, 0, NULL, NULL, NULL, NULL
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 029114f..b79b965 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -241,6 +241,8 @@
#synchronous_standby_names = '' # standby servers that provide sync rep
# comma-separated list of application_name
# from standby(s); '*' = all
+#synchronous_standby_num = 0 # number of standby servers using sync rep
+#synchronous_replication_method = '1-priority' # 1-priority, priority
#vacuum_defer_cleanup_age = 0 # number of xacts by which cleanup is delayed
# - Standby Servers -
diff --git a/src/include/replication/syncrep.h b/src/include/replication/syncrep.h
index 96e059b..a9f816c 100644
--- a/src/include/replication/syncrep.h
+++ b/src/include/replication/syncrep.h
@@ -31,8 +31,14 @@
#define SYNC_REP_WAITING 1
#define SYNC_REP_WAIT_COMPLETE 2
+/* SyncRepMethod */
+#define SYNC_REP_METHOD_1_PRIORITY 0
+#define SYNC_REP_METHOD_PRIORITY 1
+
/* user-settable parameters for synchronous replication */
extern char *SyncRepStandbyNames;
+extern int synchronous_replication_method;
+extern int synchronous_standby_num;
/* called by user backend */
extern void SyncRepWaitForLSN(XLogRecPtr XactCommitLSN);
@@ -49,9 +55,19 @@ extern void SyncRepUpdateSyncStandbysDefined(void);
/* forward declaration to avoid pulling in walsender_private.h */
struct WalSnd;
-extern struct WalSnd *SyncRepGetSynchronousStandby(void);
+
+extern int SyncRepGetSyncStandbys(int *sync_standbys);
+extern bool SyncRepSyncedLsnAdvancedTo(XLogRecPtr *write_pos, XLogRecPtr *flush_pos);
+extern bool SyncRepActiveListedWalSender(int num);
+
+/* '1-priority' and 'priority' method */
+extern int SyncRepGetSyncStandbysPriority(int *sync_standbys);
+extern bool SyncRepGetSyncLsnsPriority(XLogRecPtr *write_pos, XLogRecPtr *flush_pos);
extern bool check_synchronous_standby_names(char **newval, void **extra, GucSource source);
extern void assign_synchronous_commit(int newval, void *extra);
+/* Process configuration parameter related to synchronous replication */
+extern void ProcessSynchronousReplicationConfig(void);
+
#endif /* _SYNCREP_H */
--
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