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Support multiple synchronous standby servers.

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Previously synchronous replication offered only the ability to confirm
that all changes made by a transaction had been transferred to at most
one synchronous standby server.

This commit extends synchronous replication so that it supports multiple
synchronous standby servers. It enables users to consider one or more
standby servers as synchronous, and increase the level of transaction
durability by ensuring that transaction commits wait for replies from
all of those synchronous standbys.

Multiple synchronous standby servers are configured in
synchronous_standby_names which is extended to support new syntax of
'num_sync ( standby_name [ , ... ] )', where num_sync specifies
the number of synchronous standbys that transaction commits need to
wait for replies from and standby_name is the name of a standby
server.

The syntax of 'standby_name [ , ... ]' which was used in 9.5 or before
is also still supported. It's the same as new syntax with num_sync=1.

This commit doesn't include "quorum commit" feature which was discussed
in pgsql-hackers. Synchronous standbys are chosen based on their priorities.
synchronous_standby_names determines the priority of each standby for
being chosen as a synchronous standby. The standbys whose names appear
earlier in the list are given higher priority and will be considered as
synchronous. Other standby servers appearing later in this list
represent potential synchronous standbys.

The regression test for multiple synchronous standbys is not included
in this commit. It should come later.

Authors: Sawada Masahiko, Beena Emerson, Michael Paquier, Fujii Masao
Reviewed-By: Kyotaro Horiguchi, Amit Kapila, Robert Haas, Simon Riggs,
Amit Langote, Thomas Munro, Sameer Thakur, Suraj Kharage, Abhijit Menon-Sen,
Rajeev Rastogi

Many thanks to the various individuals who were involved in
discussing and developing this feature.
This commit is contained in:
Fujii Masao 2016-04-06 17:18:25 +09:00
parent 2143f5e127
commit 989be0810d
13 changed files with 835 additions and 200 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

49
doc/src/sgml/config.sgml
View File

@ -2906,34 +2906,69 @@ include_dir 'conf.d'
</term>
<listitem>
<para>
Specifies a comma-separated list of standby names that can support
Specifies a list of standby names that can support
<firstterm>synchronous replication</>, as described in
<xref linkend="synchronous-replication">.
At any one time there will be at most one active synchronous standby;
There will be one or more active synchronous standbys;
transactions waiting for commit will be allowed to proceed after
this standby server confirms receipt of their data.
The synchronous standby will be the first standby named in this list
these standby servers confirm receipt of their data.
The synchronous standbys will be those whose names appear
earlier in this list, and
that is both currently connected and streaming data in real-time
(as shown by a state of <literal>streaming</literal> in the
<link linkend="monitoring-stats-views-table">
<literal>pg_stat_replication</></link> view).
Other standby servers appearing later in this list represent potential
synchronous standbys.
If the current synchronous standby disconnects for whatever reason,
synchronous standbys. If any of the current synchronous
standbys disconnects for whatever reason,
it will be replaced immediately with the next-highest-priority standby.
Specifying more than one standby name can allow very high availability.
</para>
<para>
This parameter specifies a list of standby servers by using
either of the following syntaxes:
<synopsis>
<replaceable class="parameter">num_sync</replaceable> ( <replaceable class="parameter">standby_name</replaceable> [, ...] )
<replaceable class="parameter">standby_name</replaceable> [, ...]
</synopsis>
where <replaceable class="parameter">num_sync</replaceable> is
the number of synchronous standbys that transactions need to
wait for replies from,
and <replaceable class="parameter">standby_name</replaceable>
is the name of a standby server. For example, a setting of
<literal>'3 (s1, s2, s3, s4)'</> makes transaction commits wait
until their WAL records are received by three higher priority standbys
chosen from standby servers <literal>s1</>, <literal>s2</>,
<literal>s3</> and <literal>s4</>.
</para>
<para>
The second syntax was used before <productname>PostgreSQL</>
version 9.6 and is still supported. It's the same as the first syntax
with <replaceable class="parameter">num_sync</replaceable>=1.
For example, both settings of <literal>'1 (s1, s2)'</> and
<literal>'s1, s2'</> have the same meaning; either <literal>s1</>
or <literal>s2</> is chosen as a synchronous standby.
</para>
<para>
The name of a standby server for this purpose is the
<varname>application_name</> setting of the standby, as set in the
<varname>primary_conninfo</> of the standby's WAL receiver. There is
no mechanism to enforce uniqueness. In case of duplicates one of the
matching standbys will be chosen to be the synchronous standby, though
matching standbys will be considered as higher priority, though
exactly which one is indeterminate.
The special entry <literal>*</> matches any
<varname>application_name</>, including the default application name
of <literal>walreceiver</>.
</para>
<note>
<para>
The <replaceable class="parameter">standby_name</replaceable>
must be enclosed in double quotes if a comma (<literal>,</>),
a double quote (<literal>"</>), <!-- " font-lock sanity -->
a left parentheses (<literal>(</>), a right parentheses (<literal>)</>)
or a space is used in the name of a standby server.
</para>
</note>
<para>
If no synchronous standby names are specified here, then synchronous
replication is not enabled and transaction commits will not wait for

76
doc/src/sgml/high-availability.sgml
View File

@ -1027,10 +1027,12 @@ primary_slot_name = 'node_a_slot'
<para>
Synchronous replication offers the ability to confirm that all changes
made by a transaction have been transferred to one synchronous standby
server. This extends the standard level of durability
made by a transaction have been transferred to one or more synchronous
standby servers. This extends that standard level of durability
offered by a transaction commit. This level of protection is referred
to as 2-safe replication in computer science theory.
to as 2-safe replication in computer science theory, and group-1-safe
(group-safe and 1-safe) when <varname>synchronous_commit</> is set to
<literal>remote_write</>.
</para>
<para>
@ -1084,8 +1086,8 @@ primary_slot_name = 'node_a_slot'
In the case that <varname>synchronous_commit</> is set to
<literal>remote_apply</>, the standby sends reply messages when the commit
record is replayed, making the transaction visible.
If the standby is the first matching standby, as specified in
<varname>synchronous_standby_names</> on the primary, the reply
If the standby is chosen as the synchronous standby, from a priority
list of <varname>synchronous_standby_names</> on the primary, the reply
messages from that standby will be used to wake users waiting for
confirmation that the commit record has been received. These parameters
allow the administrator to specify which standby servers should be
@ -1126,6 +1128,40 @@ primary_slot_name = 'node_a_slot'
</sect3>
<sect3 id="synchronous-replication-multiple-standbys">
<title>Multiple Synchronous Standbys</title>
<para>
Synchronous replication supports one or more synchronous standby servers;
transactions will wait until all the standby servers which are considered
as synchronous confirm receipt of their data. The number of synchronous
standbys that transactions must wait for replies from is specified in
<varname>synchronous_standby_names</>. This parameter also specifies
a list of standby names, which determines the priority of each standby
for being chosen as a synchronous standby. The standbys whose names
appear earlier in the list are given higher priority and will be considered
as synchronous. Other standby servers appearing later in this list
represent potential synchronous standbys. If any of the current
synchronous standbys disconnects for whatever reason, it will be replaced
immediately with the next-highest-priority standby.
</para>
<para>
An example of <varname>synchronous_standby_names</> for multiple
synchronous standbys is:
<programlisting>
synchronous_standby_names = '2 (s1, s2, s3)'
</programlisting>
In this example, if four standby servers <literal>s1</>, <literal>s2</>,
<literal>s3</> and <literal>s4</> are running, the two standbys
<literal>s1</> and <literal>s2</> will be chosen as synchronous standbys
because their names appear early in the list of standby names.
<literal>s3</> is a potential synchronous standby and will take over
the role of synchronous standby when either of <literal>s1</> or
<literal>s2</> fails. <literal>s4</> is an asynchronous standby since
its name is not in the list.
</para>
</sect3>
<sect3 id="synchronous-replication-performance">
<title>Planning for Performance</title>
@ -1171,19 +1207,21 @@ primary_slot_name = 'node_a_slot'
<title>Planning for High Availability</title>
<para>
Commits made when <varname>synchronous_commit</> is set to <literal>on</>,
<literal>remote_apply</> or <literal>remote_write</> will wait until the
synchronous standby responds. The response may never occur if the last, or
only, standby should crash.
<varname>synchronous_standby_names</> specifies the number and
names of synchronous standbys that transaction commits made when
<varname>synchronous_commit</> is set to <literal>on</>,
<literal>remote_apply</> or <literal>remote_write</> will wait for
responses from. Such transaction commits may never be completed
if any one of synchronous standbys should crash.
</para>
<para>
The best solution for avoiding data loss is to ensure you don't lose
your last remaining synchronous standby. This can be achieved by naming multiple
The best solution for high availability is to ensure you keep as many
synchronous standbys as requested. This can be achieved by naming multiple
potential synchronous standbys using <varname>synchronous_standby_names</>.
The first named standby will be used as the synchronous standby. Standbys
listed after this will take over the role of synchronous standby if the
first one should fail.
The standbys whose names appear earlier in the list will be used as
synchronous standbys. Standbys listed after these will take over
the role of synchronous standby if one of current ones should fail.
</para>
<para>
@ -1208,13 +1246,15 @@ primary_slot_name = 'node_a_slot'
they show as committed on the primary. The guarantee we offer is that
the application will not receive explicit acknowledgement of the
successful commit of a transaction until the WAL data is known to be
safely received by the standby.
safely received by all the synchronous standbys.
</para>
<para>
If you really do lose your last standby server then you should disable
<varname>synchronous_standby_names</> and reload the configuration file
on the primary server.
If you really cannot keep as many synchronous standbys as requested
then you should decrease the number of synchronous standbys that
transaction commits must wait for responses from
in <varname>synchronous_standby_names</> (or disable it) and
reload the configuration file on the primary server.
</para>
<para>

4
src/backend/Makefile
View File

@ -203,7 +203,7 @@ distprep:
$(MAKE) -C parser gram.c gram.h scan.c
$(MAKE) -C bootstrap bootparse.c bootscanner.c
$(MAKE) -C catalog schemapg.h postgres.bki postgres.description postgres.shdescription
$(MAKE) -C replication repl_gram.c repl_scanner.c
$(MAKE) -C replication repl_gram.c repl_scanner.c syncrep_gram.c syncrep_scanner.c
$(MAKE) -C storage/lmgr lwlocknames.h
$(MAKE) -C utils fmgrtab.c fmgroids.h errcodes.h
$(MAKE) -C utils/misc guc-file.c
@ -320,6 +320,8 @@ maintainer-clean: distclean
catalog/postgres.shdescription \
replication/repl_gram.c \
replication/repl_scanner.c \
replication/syncrep_gram.c \
replication/syncrep_scanner.c \
storage/lmgr/lwlocknames.c \
storage/lmgr/lwlocknames.h \
utils/fmgroids.h \

2
src/backend/replication/.gitignore vendored
View File

@ -1,2 +1,4 @@
/repl_gram.c
/repl_scanner.c
/syncrep_gram.c
/syncrep_scanner.c

11
src/backend/replication/Makefile
View File

@ -15,7 +15,7 @@ include $(top_builddir)/src/Makefile.global
override CPPFLAGS := -I. -I$(srcdir) $(CPPFLAGS)
OBJS = walsender.o walreceiverfuncs.o walreceiver.o basebackup.o \
repl_gram.o slot.o slotfuncs.o syncrep.o
repl_gram.o slot.o slotfuncs.o syncrep.o syncrep_gram.o
SUBDIRS = logical
@ -24,5 +24,10 @@ include $(top_srcdir)/src/backend/common.mk
# repl_scanner is compiled as part of repl_gram
repl_gram.o: repl_scanner.c
# repl_gram.c and repl_scanner.c are in the distribution tarball, so
# they are not cleaned here.
# syncrep_scanner is complied as part of syncrep_gram
syncrep_gram.o: syncrep_scanner.c
syncrep_scanner.c: FLEXFLAGS = -CF -p
syncrep_scanner.c: FLEX_NO_BACKUP=yes
# repl_gram.c, repl_scanner.c, syncrep_gram.c and syncrep_scanner.c
# are in the distribution tarball, so they are not cleaned here.

607
src/backend/replication/syncrep.c
View File

@ -4,8 +4,8 @@
*
* Synchronous replication is new as of PostgreSQL 9.1.
*
* If requested, transaction commits wait until their commit LSN is
* acknowledged by the synchronous standby.
* If requested, transaction commits wait until their commit LSN are
* acknowledged by the synchronous standbys.
*
* This module contains the code for waiting and release of backends.
* All code in this module executes on the primary. The core streaming
@ -13,7 +13,7 @@
*
* The essence of this design is that it isolates all logic about
* waiting/releasing onto the primary. The primary defines which standbys
* it wishes to wait for. The standby is completely unaware of the
* it wishes to wait for. The standbys are completely unaware of the
* durability requirements of transactions on the primary, reducing the
* complexity of the code and streamlining both standby operations and
* network bandwidth because there is no requirement to ship
@ -21,19 +21,32 @@
*
* Replication is either synchronous or not synchronous (async). If it is
* async, we just fastpath out of here. If it is sync, then we wait for
* the write or flush location on the standby before releasing the waiting
* backend. Further complexity in that interaction is expected in later
* releases.
* the write, flush or apply location on the standby before releasing
* the waiting backend. Further complexity in that interaction is
* expected in later releases.
*
* The best performing way to manage the waiting backends is to have a
* 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
* will release waiters from the queue.
* In 9.5 or before only a single standby could be considered as
* synchronous. In 9.6 we support multiple synchronous standbys.
* The number of synchronous standbys that transactions must wait for
* replies from is specified in synchronous_standby_names.
* This parameter also specifies a list of standby names,
* which determines the priority of each standby for being chosen as
* a synchronous standby. The standbys whose names appear earlier
* in the list are given higher priority and will be considered as
* synchronous. Other standby servers appearing later in this list
* represent potential synchronous standbys. If any of the current
* synchronous standbys disconnects for whatever reason, it will be
* replaced immediately with the next-highest-priority standby.
*
* Before the standbys chosen from synchronous_standby_names can
* become the synchronous standbys they must have caught up with
* the primary; that may take some time. Once caught up,
* the current higher priority standbys which are considered as
* synchronous at that moment will release waiters from the queue.
*
* Portions Copyright (c) 2010-2016, PostgreSQL Global Development Group
*
@ -65,12 +78,17 @@ char *SyncRepStandbyNames;
static bool announce_next_takeover = true;
SyncRepConfigData *SyncRepConfig;
static int SyncRepWaitMode = SYNC_REP_NO_WAIT;
static void SyncRepQueueInsert(int mode);
static void SyncRepCancelWait(void);
static int SyncRepWakeQueue(bool all, int mode);
static bool SyncRepGetOldestSyncRecPtr(XLogRecPtr *writePtr,
XLogRecPtr *flushPtr,
XLogRecPtr *applyPtr,
bool *am_sync);
static int SyncRepGetStandbyPriority(void);
#ifdef USE_ASSERT_CHECKING
@ -343,6 +361,11 @@ SyncRepInitConfig(void)
{
int priority;
/* Update the config data of synchronous replication */
SyncRepFreeConfig(SyncRepConfig);
SyncRepConfig = NULL;
SyncRepUpdateConfig();
/*
* Determine if we are a potential sync standby and remember the result
* for handling replies from standby.
@ -360,23 +383,209 @@ 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.
* Update the LSNs on each queue based upon our latest state. This
* implements a simple policy of first-valid-sync-standby-releases-waiter.
*
* Other policies are possible, which would change what we do here and
* perhaps also which information we store as well.
*/
WalSnd *
SyncRepGetSynchronousStandby(void)
void
SyncRepReleaseWaiters(void)
{
WalSnd *result = NULL;
int result_priority = 0;
int i;
volatile WalSndCtlData *walsndctl = WalSndCtl;
XLogRecPtr writePtr;
XLogRecPtr flushPtr;
XLogRecPtr applyPtr;
bool got_oldest;
bool am_sync;
int numwrite = 0;
int numflush = 0;
int numapply = 0;
/*
* If this WALSender is serving a standby that is not on the list of
* potential sync standbys then we have nothing to do. If we are still
* starting up, still running base backup or the current flush position
* is still invalid, then leave quickly also.
*/
if (MyWalSnd->sync_standby_priority == 0 ||
MyWalSnd->state < WALSNDSTATE_STREAMING ||
XLogRecPtrIsInvalid(MyWalSnd->flush))
{
announce_next_takeover = true;
return;
}
/*
* We're a potential sync standby. Release waiters if there are
* enough sync standbys and we are considered as sync.
*/
LWLockAcquire(SyncRepLock, LW_EXCLUSIVE);
/*
* Check whether we are a sync standby or not, and calculate
* the oldest positions among all sync standbys.
*/
got_oldest = SyncRepGetOldestSyncRecPtr(&writePtr, &flushPtr,
&applyPtr, &am_sync);
/*
* If we are managing a sync standby, though we weren't
* prior to this, then announce we are now a sync standby.
*/
if (announce_next_takeover && am_sync)
{
announce_next_takeover = false;
ereport(LOG,
(errmsg("standby \"%s\" is now a synchronous standby with priority %u",
application_name, MyWalSnd->sync_standby_priority)));
}
/*
* If the number of sync standbys is less than requested or we aren't
* managing a sync standby then just leave.
*/
if (!got_oldest || !am_sync)
{
LWLockRelease(SyncRepLock);
announce_next_takeover = !am_sync;
return;
}
/*
* Set the lsn first so that when we wake backends they will release up to
* this location.
*/
if (walsndctl->lsn[SYNC_REP_WAIT_WRITE] < writePtr)
{
walsndctl->lsn[SYNC_REP_WAIT_WRITE] = writePtr;
numwrite = SyncRepWakeQueue(false, SYNC_REP_WAIT_WRITE);
}
if (walsndctl->lsn[SYNC_REP_WAIT_FLUSH] < flushPtr)
{
walsndctl->lsn[SYNC_REP_WAIT_FLUSH] = flushPtr;
numflush = SyncRepWakeQueue(false, SYNC_REP_WAIT_FLUSH);
}
if (walsndctl->lsn[SYNC_REP_WAIT_APPLY] < applyPtr)
{
walsndctl->lsn[SYNC_REP_WAIT_APPLY] = applyPtr;
numapply = SyncRepWakeQueue(false, SYNC_REP_WAIT_APPLY);
}
LWLockRelease(SyncRepLock);
elog(DEBUG3, "released %d procs up to write %X/%X, %d procs up to flush %X/%X, %d procs up to apply %X/%x",
numwrite, (uint32) (writePtr >> 32), (uint32) writePtr,
numflush, (uint32) (flushPtr >> 32), (uint32) flushPtr,
numapply, (uint32) (applyPtr >> 32), (uint32) applyPtr);
}
/*
* Calculate the oldest Write, Flush and Apply positions among sync standbys.
*
* Return false if the number of sync standbys is less than
* synchronous_standby_names specifies. Otherwise return true and
* store the oldest positions into *writePtr, *flushPtr and *applyPtr.
*
* On return, *am_sync is set to true if this walsender is connecting to
* sync standby. Otherwise it's set to false.
*/
static bool
SyncRepGetOldestSyncRecPtr(XLogRecPtr *writePtr, XLogRecPtr *flushPtr,
XLogRecPtr *applyPtr, bool *am_sync)
{
List *sync_standbys;
ListCell *cell;
*writePtr = InvalidXLogRecPtr;
*flushPtr = InvalidXLogRecPtr;
*applyPtr = InvalidXLogRecPtr;
*am_sync = false;
/* Get standbys that are considered as synchronous at this moment */
sync_standbys = SyncRepGetSyncStandbys(am_sync);
/*
* Quick exit if we are not managing a sync standby or there are not
* enough synchronous standbys.
*/
if (!(*am_sync) || list_length(sync_standbys) < SyncRepConfig->num_sync)
{
list_free(sync_standbys);
return false;
}
/*
* Scan through all sync standbys and calculate the oldest
* Write, Flush and Apply positions.
*/
foreach (cell, sync_standbys)
{
WalSnd *walsnd = &WalSndCtl->walsnds[lfirst_int(cell)];
XLogRecPtr write;
XLogRecPtr flush;
XLogRecPtr apply;
SpinLockAcquire(&walsnd->mutex);
write = walsnd->write;
flush = walsnd->flush;
apply = walsnd->apply;
SpinLockRelease(&walsnd->mutex);
if (XLogRecPtrIsInvalid(*writePtr) || *writePtr > write)
*writePtr = write;
if (XLogRecPtrIsInvalid(*flushPtr) || *flushPtr > flush)
*flushPtr = flush;
if (XLogRecPtrIsInvalid(*applyPtr) || *applyPtr > apply)
*applyPtr = apply;
}
list_free(sync_standbys);
return true;
}
/*
* Return the list of sync standbys, or NIL if no sync standby is connected.
*
* If there are multiple standbys with the same priority,
* the first one found is selected preferentially.
* The caller must hold SyncRepLock.
*
* On return, *am_sync is set to true if this walsender is connecting to
* sync standby. Otherwise it's set to false.
*/
List *
SyncRepGetSyncStandbys(bool *am_sync)
{
List *result = NIL;
List *pending = NIL;
int lowest_priority;
int next_highest_priority;
int this_priority;
int priority;
int i;
bool am_in_pending = false;
volatile WalSnd *walsnd; /* Use volatile pointer to prevent
* code rearrangement */
/* Quick exit if sync replication is not requested */
if (SyncRepConfig == NULL)
return NIL;
if (am_sync != NULL)
*am_sync = false;
lowest_priority = list_length(SyncRepConfig->members);
next_highest_priority = lowest_priority + 1;
/*
* Find the sync standbys which have the highest priority (i.e, 1).
* Also store all the other potential sync standbys into the pending list,
* in order to scan it later and find other sync standbys from it quickly.
*/
for (i = 0; i < max_wal_senders; i++)
{
/* Use volatile pointer to prevent code rearrangement */
volatile WalSnd *walsnd = &WalSndCtl->walsnds[i];
int this_priority;
walsnd = &WalSndCtl->walsnds[i];
/* Must be active */
if (walsnd->pid == 0)
@ -391,115 +600,125 @@ SyncRepGetSynchronousStandby(void)
if (this_priority == 0)
continue;
/* Must have a lower priority value than any previous ones */
if (result != NULL && result_priority <= this_priority)
continue;
/* Must have a valid flush position */
if (XLogRecPtrIsInvalid(walsnd->flush))
continue;
result = (WalSnd *) walsnd;
result_priority = this_priority;
/*
* If priority is equal to 1, there cannot be any other WAL senders
* with a lower priority, so we're done.
* If the priority is equal to 1, consider this standby as sync
* and append it to the result. Otherwise append this standby
* to the pending list to check if it's actually sync or not later.
*/
if (this_priority == 1)
return result;
{
result = lappend_int(result, i);
if (am_sync != NULL && walsnd == MyWalSnd)
*am_sync = true;
if (list_length(result) == SyncRepConfig->num_sync)
{
list_free(pending);
return result; /* Exit if got enough sync standbys */
}
}
else
{
pending = lappend_int(pending, i);
if (am_sync != NULL && walsnd == MyWalSnd)
am_in_pending = true;
/*
* Track the highest priority among the standbys in the pending
* list, in order to use it as the starting priority for later scan
* of the list. This is useful to find quickly the sync standbys
* from the pending list later because we can skip unnecessary
* scans for the unused priorities.
*/
if (this_priority < next_highest_priority)
next_highest_priority = this_priority;
}
}
/*
* Consider all pending standbys as sync if the number of them plus
* already-found sync ones is lower than the configuration requests.
*/
if (list_length(result) + list_length(pending) <= SyncRepConfig->num_sync)
{
bool needfree = (result != NIL && pending != NIL);
/*
* Set *am_sync to true if this walsender is in the pending list
* because all pending standbys are considered as sync.
*/
if (am_sync != NULL && !(*am_sync))
*am_sync = am_in_pending;
result = list_concat(result, pending);
if (needfree)
pfree(pending);
return result;
}
/*
* Find the sync standbys from the pending list.
*/
priority = next_highest_priority;
while (priority <= lowest_priority)
{
ListCell *cell;
ListCell *prev = NULL;
ListCell *next;
next_highest_priority = lowest_priority + 1;
for (cell = list_head(pending); cell != NULL; cell = next)
{
i = lfirst_int(cell);
walsnd = &WalSndCtl->walsnds[i];
next = lnext(cell);
this_priority = walsnd->sync_standby_priority;
if (this_priority == priority)
{
result = lappend_int(result, i);
if (am_sync != NULL && walsnd == MyWalSnd)
*am_sync = true;
/*
* We should always exit here after the scan of pending list
* starts because we know that the list has enough elements
* to reach SyncRepConfig->num_sync.
*/
if (list_length(result) == SyncRepConfig->num_sync)
{
list_free(pending);
return result; /* Exit if got enough sync standbys */
}
/*
* Remove the entry for this sync standby from the list
* to prevent us from looking at the same entry again.
*/
pending = list_delete_cell(pending, cell, prev);
continue;
}
if (this_priority < next_highest_priority)
next_highest_priority = this_priority;
prev = cell;
}
priority = next_highest_priority;
}
/* never reached, but keep compiler quiet */
Assert(false);
return result;
}
/*
* Update the LSNs on each queue based upon our latest state. This
* implements a simple policy of first-valid-standby-releases-waiter.
*
* Other policies are possible, which would change what we do here and
* perhaps also which information we store as well.
*/
void
SyncRepReleaseWaiters(void)
{
volatile WalSndCtlData *walsndctl = WalSndCtl;
WalSnd *syncWalSnd;
int numwrite = 0;
int numflush = 0;
int numapply = 0;
/*
* If this WALSender is serving a standby that is not on the list of
* potential sync standbys then we have nothing to do. If we are still
* starting up, still running base backup or the current flush position
* is still invalid, then leave quickly also.
*/
if (MyWalSnd->sync_standby_priority == 0 ||
MyWalSnd->state < WALSNDSTATE_STREAMING ||
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)
{
LWLockRelease(SyncRepLock);
announce_next_takeover = true;
return;
}
/*
* 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)
{
walsndctl->lsn[SYNC_REP_WAIT_WRITE] = MyWalSnd->write;
numwrite = SyncRepWakeQueue(false, SYNC_REP_WAIT_WRITE);
}
if (walsndctl->lsn[SYNC_REP_WAIT_FLUSH] < MyWalSnd->flush)
{
walsndctl->lsn[SYNC_REP_WAIT_FLUSH] = MyWalSnd->flush;
numflush = SyncRepWakeQueue(false, SYNC_REP_WAIT_FLUSH);
}
if (walsndctl->lsn[SYNC_REP_WAIT_APPLY] < MyWalSnd->apply)
{
walsndctl->lsn[SYNC_REP_WAIT_APPLY] = MyWalSnd->apply;
numapply = SyncRepWakeQueue(false, SYNC_REP_WAIT_APPLY);
}
LWLockRelease(SyncRepLock);
elog(DEBUG3, "released %d procs up to write %X/%X, %d procs up to flush %X/%X, %d procs up to apply %X/%X",
numwrite, (uint32) (MyWalSnd->write >> 32), (uint32) MyWalSnd->write,
numflush, (uint32) (MyWalSnd->flush >> 32), (uint32) MyWalSnd->flush,
numapply, (uint32) (MyWalSnd->apply >> 32), (uint32) MyWalSnd->apply);
/*
* If we are managing the highest priority standby, though we weren't
* prior to this, then announce we are now the sync standby.
*/
if (announce_next_takeover)
{
announce_next_takeover = false;
ereport(LOG,
(errmsg("standby \"%s\" is now the synchronous standby with priority %u",
application_name, MyWalSnd->sync_standby_priority)));
}
}
/*
* Check if we are in the list of sync standbys, and if so, determine
* priority sequence. Return priority if set, or zero to indicate that
@ -511,8 +730,7 @@ SyncRepReleaseWaiters(void)
static int
SyncRepGetStandbyPriority(void)
{
char *rawstring;
List *elemlist;
List *members;
ListCell *l;
int priority = 0;
bool found = false;
@ -524,20 +742,11 @@ SyncRepGetStandbyPriority(void)
if (am_cascading_walsender)
return 0;
/* Need a modifiable copy of string */
rawstring = pstrdup(SyncRepStandbyNames);
/* Parse string into list of identifiers */
if (!SplitIdentifierString(rawstring, ',', &elemlist))
{
/* syntax error in list */
pfree(rawstring);
list_free(elemlist);
/* GUC machinery will have already complained - no need to do again */
if (!SyncStandbysDefined())
return 0;
}
foreach(l, elemlist)
members = SyncRepConfig->members;
foreach(l, members)
{
char *standby_name = (char *) lfirst(l);
@ -551,9 +760,6 @@ SyncRepGetStandbyPriority(void)
}
}
pfree(rawstring);
list_free(elemlist);
return (found ? priority : 0);
}
@ -661,6 +867,45 @@ SyncRepUpdateSyncStandbysDefined(void)
}
}
/*
* Parse synchronous_standby_names and update the config data
* of synchronous standbys.
*/
void
SyncRepUpdateConfig(void)
{
int parse_rc;
if (!SyncStandbysDefined())
return;
/*
* check_synchronous_standby_names() verifies the setting value of
* synchronous_standby_names before this function is called. So
* syncrep_yyparse() must not cause an error here.
*/
syncrep_scanner_init(SyncRepStandbyNames);
parse_rc = syncrep_yyparse();
Assert(parse_rc == 0);
syncrep_scanner_finish();
SyncRepConfig = syncrep_parse_result;
syncrep_parse_result = NULL;
}
/*
* Free a previously-allocated config data of synchronous replication.
*/
void
SyncRepFreeConfig(SyncRepConfigData *config)
{
if (!config)
return;
list_free_deep(config->members);
pfree(config);
}
#ifdef USE_ASSERT_CHECKING
static bool
SyncRepQueueIsOrderedByLSN(int mode)
@ -705,33 +950,75 @@ SyncRepQueueIsOrderedByLSN(int mode)
bool
check_synchronous_standby_names(char **newval, void **extra, GucSource source)
{
char *rawstring;
List *elemlist;
int parse_rc;
/* Need a modifiable copy of string */
rawstring = pstrdup(*newval);
/* Parse string into list of identifiers */
if (!SplitIdentifierString(rawstring, ',', &elemlist))
if (*newval != NULL && (*newval)[0] != '\0')
{
/* syntax error in list */
GUC_check_errdetail("List syntax is invalid.");
pfree(rawstring);
list_free(elemlist);
return false;
syncrep_scanner_init(*newval);
parse_rc = syncrep_yyparse();
syncrep_scanner_finish();
if (parse_rc != 0)
{
GUC_check_errcode(ERRCODE_SYNTAX_ERROR);
GUC_check_errdetail("synchronous_standby_names parser returned %d",
parse_rc);
return false;
}
/*
* Warn if num_sync exceeds the number of names of potential sync
* standbys. This setting doesn't make sense in most cases because
* it implies that enough number of sync standbys will not appear,
* which makes transaction commits wait for sync replication
* infinitely.
*
* If there are more than one standbys having the same name and
* priority, we can see enough sync standbys to complete transaction
* commits. However it's not recommended to run multiple standbys
* with the same priority because we cannot gain full control of
* the selection of sync standbys from them.
*
* OTOH, that setting is OK if we understand the above problem
* regarding the selection of sync standbys and intentionally
* specify * to match all the standbys.
*/
if (syncrep_parse_result->num_sync >
list_length(syncrep_parse_result->members))
{
ListCell *l;
bool has_asterisk = false;
foreach(l, syncrep_parse_result->members)
{
char *standby_name = (char *) lfirst(l);
if (pg_strcasecmp(standby_name, "*") == 0)
{
has_asterisk = true;
break;
}
}
/*
* Only the postmaster warns this inappropriate setting
* to avoid cluttering the log.
*/
if (!has_asterisk && !IsUnderPostmaster)
ereport(WARNING,
(errmsg("The configured number of synchronous standbys (%d) exceeds the number of names of potential synchronous ones (%d)",
syncrep_parse_result->num_sync, list_length(syncrep_parse_result->members)),
errhint("Specify more names of potential synchronous standbys in synchronous_standby_names.")));
}
/*
* syncrep_yyparse sets the global syncrep_parse_result as side effect.
* But this function is required to just check, so frees it
* after parsing the parameter.
*/
SyncRepFreeConfig(syncrep_parse_result);
}
/*
* Any additional validation of standby names should go here.
*
* Don't attempt to set WALSender priority because this is executed by
* postmaster at startup, not WALSender, so the application_name is not
* yet correctly set.
*/
pfree(rawstring);
list_free(elemlist);
return true;
}

86
src/backend/replication/syncrep_gram.y Normal file
View File

@ -0,0 +1,86 @@
%{
/*-------------------------------------------------------------------------
*
* syncrep_gram.y - Parser for synchronous_standby_names
*
* Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* src/backend/replication/syncrep_gram.y
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "replication/syncrep.h"
#include "utils/formatting.h"
/* Result of the parsing is returned here */
SyncRepConfigData *syncrep_parse_result;
static SyncRepConfigData *create_syncrep_config(char *num_sync, List *members);
/*
* Bison doesn't allocate anything that needs to live across parser calls,
* so we can easily have it use palloc instead of malloc. This prevents
* memory leaks if we error out during parsing. Note this only works with
* bison >= 2.0. However, in bison 1.875 the default is to use alloca()
* if possible, so there's not really much problem anyhow, at least if
* you're building with gcc.
*/
#define YYMALLOC palloc
#define YYFREE pfree
%}
%expect 0
%name-prefix="syncrep_yy"
%union
{
char *str;
List *list;
SyncRepConfigData *config;
}
%token <str> NAME NUM
%type <config> result standby_config
%type <list> standby_list
%type <str> standby_name
%start result
%%
result:
standby_config { syncrep_parse_result = $1; }
;
standby_config:
standby_list { $$ = create_syncrep_config("1", $1); }
| NUM '(' standby_list ')' { $$ = create_syncrep_config($1, $3); }
;
standby_list:
standby_name { $$ = list_make1($1);}
| standby_list ',' standby_name { $$ = lappend($1, $3);}
;
standby_name:
NAME { $$ = $1; }
| NUM { $$ = $1; }
;
%%
static SyncRepConfigData *
create_syncrep_config(char *num_sync, List *members)
{
SyncRepConfigData *config =
(SyncRepConfigData *) palloc(sizeof(SyncRepConfigData));
config->num_sync = atoi(num_sync);
config->members = members;
return config;
}
#include "syncrep_scanner.c"

144
src/backend/replication/syncrep_scanner.l Normal file
View File

@ -0,0 +1,144 @@
%{
/*-------------------------------------------------------------------------
*
* syncrep_scanner.l
* a lexical scanner for synchronous_standby_names
*
* Portions Copyright (c) 1996-2016, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* src/backend/replication/syncrep_scanner.l
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "miscadmin.h"
#include "lib/stringinfo.h"
/*
* flex emits a yy_fatal_error() function that it calls in response to
* critical errors like malloc failure, file I/O errors, and detection of
* internal inconsistency. That function prints a message and calls exit().
* Mutate it to instead call ereport(FATAL), which terminates this process.
*
* The process that causes this fatal error should be terminated.
* Otherwise it has to abandon the new setting value of
* synchronous_standby_names and keep running with the previous one
* while the other processes switch to the new one.
* This inconsistency of the setting that each process is based on
* can cause a serious problem. Though it's basically not good idea to
* use FATAL here because it can take down the postmaster,
* we should do that in order to avoid such an inconsistency.
*/
#undef fprintf
#define fprintf(file, fmt, msg) syncrep_flex_fatal(fmt, msg)
static void
syncrep_flex_fatal(const char *fmt, const char *msg)
{
ereport(FATAL, (errmsg_internal("%s", msg)));
}
/* Handles to the buffer that the lexer uses internally */
static YY_BUFFER_STATE scanbufhandle;
static StringInfoData xdbuf;
%}
%option 8bit
%option never-interactive
%option nounput
%option noinput
%option noyywrap
%option warn
%option prefix="syncrep_yy"
/*
* <xd> delimited identifiers (double-quoted identifiers)
*/
%x xd
space [ \t\n\r\f\v]
undquoted_start [^ ,\(\)\"]
undquoted_cont [^ ,\(\)]
undquoted_name {undquoted_start}{undquoted_cont}*
dquoted_name [^\"]+
/* Double-quoted string */
dquote \"
xdstart {dquote}
xddouble {dquote}{dquote}
xdstop {dquote}
xdinside {dquoted_name}
%%
{space}+ { /* ignore */ }
{xdstart} {
initStringInfo(&xdbuf);
BEGIN(xd);
}
<xd>{xddouble} {
appendStringInfoChar(&xdbuf, '\"');
}
<xd>{xdinside} {
appendStringInfoString(&xdbuf, yytext);
}
<xd>{xdstop} {
yylval.str = pstrdup(xdbuf.data);
pfree(xdbuf.data);
BEGIN(INITIAL);
return NAME;
}
"," { return ','; }
"(" { return '('; }
")" { return ')'; }
[1-9][0-9]* {
yylval.str = pstrdup(yytext);
return NUM;
}
{undquoted_name} {
yylval.str = pstrdup(yytext);
return NAME;
}
%%
void
yyerror(const char *message)
{
ereport(IsUnderPostmaster ? DEBUG2 : LOG,
(errcode(ERRCODE_SYNTAX_ERROR),
errmsg("%s at or near \"%s\"", message, yytext)));
}
void
syncrep_scanner_init(const char *str)
{
Size slen = strlen(str);
char *scanbuf;
/*
* Might be left over after ereport()
*/
if (YY_CURRENT_BUFFER)
yy_delete_buffer(YY_CURRENT_BUFFER);
/*
* Make a scan buffer with special termination needed by flex.
*/
scanbuf = (char *) palloc(slen + 2);
memcpy(scanbuf, str, slen);
scanbuf[slen] = scanbuf[slen + 1] = YY_END_OF_BUFFER_CHAR;
scanbufhandle = yy_scan_buffer(scanbuf, slen + 2);
}
void
syncrep_scanner_finish(void)
{
yy_delete_buffer(scanbufhandle);
scanbufhandle = NULL;
}

19
src/backend/replication/walsender.c
View File

@ -2751,7 +2751,7 @@ pg_stat_get_wal_senders(PG_FUNCTION_ARGS)
Tuplestorestate *tupstore;
MemoryContext per_query_ctx;
MemoryContext oldcontext;
WalSnd *sync_standby;
List *sync_standbys;
int i;
/* check to see if caller supports us returning a tuplestore */
@ -2780,12 +2780,23 @@ pg_stat_get_wal_senders(PG_FUNCTION_ARGS)
MemoryContextSwitchTo(oldcontext);
/*
* Get the currently active synchronous standby.
* Allocate and update the config data of synchronous replication,
* and then get the currently active synchronous standbys.
*/
SyncRepUpdateConfig();
LWLockAcquire(SyncRepLock, LW_SHARED);
sync_standby = SyncRepGetSynchronousStandby();
sync_standbys = SyncRepGetSyncStandbys(NULL);
LWLockRelease(SyncRepLock);
/*
* Free the previously-allocated config data because a backend
* no longer needs it. The next call of this function needs to
* allocate and update the config data newly because the setting
* of sync replication might be changed between the calls.
*/
SyncRepFreeConfig(SyncRepConfig);
SyncRepConfig = NULL;
for (i = 0; i < max_wal_senders; i++)
{
WalSnd *walsnd = &WalSndCtl->walsnds[i];
@ -2856,7 +2867,7 @@ pg_stat_get_wal_senders(PG_FUNCTION_ARGS)
*/
if (priority == 0)
values[7] = CStringGetTextDatum("async");
else if (walsnd == sync_standby)
else if (list_member_int(sync_standbys, i))
values[7] = CStringGetTextDatum("sync");
else
values[7] = CStringGetTextDatum("potential");

2
src/backend/utils/misc/guc.c
View File

@ -3448,7 +3448,7 @@ static struct config_string ConfigureNamesString[] =
{
{"synchronous_standby_names", PGC_SIGHUP, REPLICATION_MASTER,
gettext_noop("List of names of potential synchronous standbys."),
gettext_noop("Number of synchronous standbys and list of names of potential synchronous ones."),
NULL,
GUC_LIST_INPUT
},

2
src/backend/utils/misc/postgresql.conf.sample
View File

@ -240,7 +240,7 @@
# These settings are ignored on a standby server.
#synchronous_standby_names = '' # standby servers that provide sync rep
# comma-separated list of application_name
# number of sync standbys and comma-separated list of application_name
# from standby(s); '*' = all
#vacuum_defer_cleanup_age = 0 # number of xacts by which cleanup is delayed

31
src/include/replication/syncrep.h
View File

@ -32,6 +32,18 @@
#define SYNC_REP_WAITING 1
#define SYNC_REP_WAIT_COMPLETE 2
/*
* Struct for the configuration of synchronous replication.
*/
typedef struct SyncRepConfigData
{
int num_sync; /* number of sync standbys that we need to wait for */
List *members; /* list of names of potential sync standbys */
} SyncRepConfigData;
extern SyncRepConfigData *syncrep_parse_result;
extern SyncRepConfigData *SyncRepConfig;
/* user-settable parameters for synchronous replication */
extern char *SyncRepStandbyNames;
@ -45,14 +57,25 @@ extern void SyncRepCleanupAtProcExit(void);
extern void SyncRepInitConfig(void);
extern void SyncRepReleaseWaiters(void);
/* called by wal sender and user backend */
extern List *SyncRepGetSyncStandbys(bool *am_sync);
extern void SyncRepUpdateConfig(void);
extern void SyncRepFreeConfig(SyncRepConfigData *config);
/* called by checkpointer */
extern void SyncRepUpdateSyncStandbysDefined(void);
/* forward declaration to avoid pulling in walsender_private.h */
struct WalSnd;
extern struct WalSnd *SyncRepGetSynchronousStandby(void);
extern bool check_synchronous_standby_names(char **newval, void **extra, GucSource source);
extern void assign_synchronous_commit(int newval, void *extra);
/*
* Internal functions for parsing synchronous_standby_names grammar,
* in syncrep_gram.y and syncrep_scanner.l
*/
extern int syncrep_yyparse(void);
extern int syncrep_yylex(void);
extern void syncrep_yyerror(const char *str);
extern void syncrep_scanner_init(const char *query_string);
extern void syncrep_scanner_finish(void);
#endif /* _SYNCREP_H */

2
src/tools/msvc/Mkvcbuild.pm
View File

@ -156,7 +156,7 @@ sub mkvcbuild
'bootparse.y');
$postgres->AddFiles('src/backend/utils/misc', 'guc-file.l');
$postgres->AddFiles('src/backend/replication', 'repl_scanner.l',
'repl_gram.y');
'repl_gram.y', 'syncrep_scanner.l', 'syncrep_gram.y');
$postgres->AddDefine('BUILDING_DLL');
$postgres->AddLibrary('secur32.lib');
$postgres->AddLibrary('ws2_32.lib');