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Commitea92368

Browse files
committed
Move max_wal_senders out of max_connections for connection slot handling
Since its introduction, max_wal_senders is counted as part ofmax_connections when it comes to define how many connection slots can beused for replication connections with a WAL sender context. This canlead to confusion for some users, as it could be possible to block abase backup or replication from happening because other backend sessionsare already taken for other purposes by an application, andsuperuser-only connection slots are not a correct solution to handlethat case.This commit makes max_wal_senders independent of max_connections for itshandling of PGPROC entries in ProcGlobal, meaning that connection slotsfor WAL senders are handled using their own free queue, like autovacuumworkers and bgworkers.One compatibility issue that this change creates is that a standby nowrequires to have a value of max_wal_senders at least equal to itsprimary. So, if a standby created enforces the value ofmax_wal_senders to be lower than that, then this could break failovers.Normally this should not be an issue though, as any settings of astandby are inherited from its primary as postgresql.conf gets normallycopied as part of a base backup, so parameters would be consistent.Author: Alexander KukushkinReviewed-by: Kyotaro Horiguchi, Petr Jelínek, Masahiko Sawada, OleksiiKliukinDiscussion:https://postgr.es/m/CAFh8B=nBzHQeYAu0b8fjK-AF1X4+_p6GRtwG+cCgs6Vci2uRuQ@mail.gmail.com
1 parent1d92a0c commitea92368

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15 files changed

+100
-55
lines changed

15 files changed

+100
-55
lines changed

‎doc/src/sgml/config.sgml

Lines changed: 17 additions & 17 deletions
Original file line numberDiff line numberDiff line change
@@ -697,8 +697,7 @@ include_dir 'conf.d'
697697

698698
<para>
699699
The default value is three connections. The value must be less
700-
than <varname>max_connections</varname> minus
701-
<xref linkend="guc-max-wal-senders"/>.
700+
than <varname>max_connections</varname>.
702701
This parameter can only be set at server start.
703702
</para>
704703
</listitem>
@@ -3495,24 +3494,25 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"' # Windows
34953494
</term>
34963495
<listitem>
34973496
<para>
3498-
Specifies the maximum number of concurrent connections from
3499-
standby servers or streaming base backup clients (i.e., the
3500-
maximum number of simultaneously running WAL sender
3501-
processes). The default is 10. The value 0 means replication is
3502-
disabled. WAL sender processes count towards the total number
3503-
of connections, so this parameter's value must be less than
3504-
<xref linkend="guc-max-connections"/> minus
3505-
<xref linkend="guc-superuser-reserved-connections"/>.
3506-
Abrupt streaming client disconnection might leave an orphaned
3507-
connection slot behind until
3508-
a timeout is reached, so this parameter should be set slightly
3509-
higher than the maximum number of expected clients so disconnected
3510-
clients can immediately reconnect. This parameter can only
3511-
be set at server start.
3512-
Also, <varname>wal_level</varname> must be set to
3497+
Specifies the maximum number of concurrent connections from standby
3498+
servers or streaming base backup clients (i.e., the maximum number of
3499+
simultaneously running WAL sender processes). The default is
3500+
<literal>10</literal>. The value <literal>0</literal> means
3501+
replication is disabled. Abrupt streaming client disconnection might
3502+
leave an orphaned connection slot behind until a timeout is reached,
3503+
so this parameter should be set slightly higher than the maximum
3504+
number of expected clients so disconnected clients can immediately
3505+
reconnect. This parameter can only be set at server start. Also,
3506+
<varname>wal_level</varname> must be set to
35133507
<literal>replica</literal> or higher to allow connections from standby
35143508
servers.
35153509
</para>
3510+
3511+
<para>
3512+
When running a standby server, you must set this parameter to the
3513+
same or higher value than on the master server. Otherwise, queries
3514+
will not be allowed in the standby server.
3515+
</para>
35163516
</listitem>
35173517
</varlistentry>
35183518

‎doc/src/sgml/high-availability.sgml

Lines changed: 5 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2177,6 +2177,11 @@ LOG: database system is ready to accept read only connections
21772177
<varname>max_locks_per_transaction</varname>
21782178
</para>
21792179
</listitem>
2180+
<listitem>
2181+
<para>
2182+
<varname>max_wal_senders</varname>
2183+
</para>
2184+
</listitem>
21802185
<listitem>
21812186
<para>
21822187
<varname>max_worker_processes</varname>

‎doc/src/sgml/runtime.sgml

Lines changed: 5 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -720,13 +720,13 @@ psql: could not connect to server: No such file or directory
720720
<row>
721721
<entry><varname>SEMMNI</varname></entry>
722722
<entry>Maximum number of semaphore identifiers (i.e., sets)</entry>
723-
<entry>at least <literal>ceil((max_connections + autovacuum_max_workers + max_worker_processes + 5) / 16)</literal> plus room for other applications</entry>
723+
<entry>at least <literal>ceil((max_connections + autovacuum_max_workers +wax_wal_senders +max_worker_processes + 5) / 16)</literal> plus room for other applications</entry>
724724
</row>
725725

726726
<row>
727727
<entry><varname>SEMMNS</varname></entry>
728728
<entry>Maximum number of semaphores system-wide</entry>
729-
<entry><literal>ceil((max_connections + autovacuum_max_workers + max_worker_processes + 5) / 16) * 17</literal> plus room for other applications</entry>
729+
<entry><literal>ceil((max_connections + autovacuum_max_workers +max_wal_senders +max_worker_processes + 5) / 16) * 17</literal> plus room for other applications</entry>
730730
</row>
731731

732732
<row>
@@ -785,13 +785,13 @@ psql: could not connect to server: No such file or directory
785785
other applications. The maximum number of semaphores in the system
786786
is set by <varname>SEMMNS</varname>, which consequently must be at least
787787
as high as <varname>max_connections</varname> plus
788-
<varname>autovacuum_max_workers</varname> plus <varname>max_worker_processes</varname>,
789-
plus one extra for each 16
788+
<varname>autovacuum_max_workers</varname> plus <varname>max_wal_senders</varname>,
789+
plus<varname>max_worker_processes</varname>, plusone extra for each 16
790790
allowed connections plus workers (see the formula in <xref
791791
linkend="sysvipc-parameters"/>). The parameter <varname>SEMMNI</varname>
792792
determines the limit on the number of semaphore sets that can
793793
exist on the system at one time. Hence this parameter must be at
794-
least <literal>ceil((max_connections + autovacuum_max_workers + max_worker_processes + 5) / 16)</literal>.
794+
least <literal>ceil((max_connections + autovacuum_max_workers +max_wal_senders +max_worker_processes + 5) / 16)</literal>.
795795
Lowering the number
796796
of allowed connections is a temporary workaround for failures,
797797
which are usually confusingly worded <quote>No space

‎src/backend/access/rmgrdesc/xlogdesc.c

Lines changed: 4 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -110,10 +110,11 @@ xlog_desc(StringInfo buf, XLogReaderState *record)
110110
}
111111

112112
appendStringInfo(buf,"max_connections=%d max_worker_processes=%d "
113-
"max_prepared_xacts=%dmax_locks_per_xact=%d "
114-
"wal_level=%s wal_log_hints=%s "
115-
"track_commit_timestamp=%s",
113+
"max_wal_senders=%dmax_prepared_xacts=%d "
114+
"max_locks_per_xact=%d wal_level=%s "
115+
"wal_log_hints=%strack_commit_timestamp=%s",
116116
xlrec.MaxConnections,
117+
xlrec.max_wal_senders,
117118
xlrec.max_worker_processes,
118119
xlrec.max_prepared_xacts,
119120
xlrec.max_locks_per_xact,

‎src/backend/access/transam/xlog.c

Lines changed: 9 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -5257,6 +5257,7 @@ BootStrapXLOG(void)
52575257
/* Set important parameter values for use when replaying WAL */
52585258
ControlFile->MaxConnections=MaxConnections;
52595259
ControlFile->max_worker_processes=max_worker_processes;
5260+
ControlFile->max_wal_senders=max_wal_senders;
52605261
ControlFile->max_prepared_xacts=max_prepared_xacts;
52615262
ControlFile->max_locks_per_xact=max_locks_per_xact;
52625263
ControlFile->wal_level=wal_level;
@@ -6170,6 +6171,9 @@ CheckRequiredParameterValues(void)
61706171
RecoveryRequiresIntParameter("max_worker_processes",
61716172
max_worker_processes,
61726173
ControlFile->max_worker_processes);
6174+
RecoveryRequiresIntParameter("max_wal_senders",
6175+
max_wal_senders,
6176+
ControlFile->max_wal_senders);
61736177
RecoveryRequiresIntParameter("max_prepared_transactions",
61746178
max_prepared_xacts,
61756179
ControlFile->max_prepared_xacts);
@@ -9460,6 +9464,7 @@ XLogReportParameters(void)
94609464
wal_log_hints!=ControlFile->wal_log_hints||
94619465
MaxConnections!=ControlFile->MaxConnections||
94629466
max_worker_processes!=ControlFile->max_worker_processes||
9467+
max_wal_senders!=ControlFile->max_wal_senders||
94639468
max_prepared_xacts!=ControlFile->max_prepared_xacts||
94649469
max_locks_per_xact!=ControlFile->max_locks_per_xact||
94659470
track_commit_timestamp!=ControlFile->track_commit_timestamp)
@@ -9478,6 +9483,7 @@ XLogReportParameters(void)
94789483

94799484
xlrec.MaxConnections=MaxConnections;
94809485
xlrec.max_worker_processes=max_worker_processes;
9486+
xlrec.max_wal_senders=max_wal_senders;
94819487
xlrec.max_prepared_xacts=max_prepared_xacts;
94829488
xlrec.max_locks_per_xact=max_locks_per_xact;
94839489
xlrec.wal_level=wal_level;
@@ -9493,6 +9499,7 @@ XLogReportParameters(void)
94939499

94949500
ControlFile->MaxConnections=MaxConnections;
94959501
ControlFile->max_worker_processes=max_worker_processes;
9502+
ControlFile->max_wal_senders=max_wal_senders;
94969503
ControlFile->max_prepared_xacts=max_prepared_xacts;
94979504
ControlFile->max_locks_per_xact=max_locks_per_xact;
94989505
ControlFile->wal_level=wal_level;
@@ -9896,6 +9903,7 @@ xlog_redo(XLogReaderState *record)
98969903
LWLockAcquire(ControlFileLock,LW_EXCLUSIVE);
98979904
ControlFile->MaxConnections=xlrec.MaxConnections;
98989905
ControlFile->max_worker_processes=xlrec.max_worker_processes;
9906+
ControlFile->max_wal_senders=xlrec.max_wal_senders;
98999907
ControlFile->max_prepared_xacts=xlrec.max_prepared_xacts;
99009908
ControlFile->max_locks_per_xact=xlrec.max_locks_per_xact;
99019909
ControlFile->wal_level=xlrec.wal_level;
@@ -9927,7 +9935,7 @@ xlog_redo(XLogReaderState *record)
99279935
UpdateControlFile();
99289936
LWLockRelease(ControlFileLock);
99299937

9930-
/* Check to see if anychanges to max_connections give problems */
9938+
/* Check to see if anyparameter change gives a problem on recovery */
99319939
CheckRequiredParameterValues();
99329940
}
99339941
elseif (info==XLOG_FPW_CHANGE)

‎src/backend/postmaster/postmaster.c

Lines changed: 4 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -885,11 +885,11 @@ PostmasterMain(int argc, char *argv[])
885885
/*
886886
* Check for invalid combinations of GUC settings.
887887
*/
888-
if (ReservedBackends+max_wal_senders>=MaxConnections)
888+
if (ReservedBackends >=MaxConnections)
889889
{
890-
write_stderr("%s: superuser_reserved_connections (%d)plus max_wal_senders (%d)must be less than max_connections (%d)\n",
890+
write_stderr("%s: superuser_reserved_connections (%d) must be less than max_connections (%d)\n",
891891
progname,
892-
ReservedBackends,max_wal_senders,MaxConnections);
892+
ReservedBackends,MaxConnections);
893893
ExitPostmaster(1);
894894
}
895895
if (XLogArchiveMode>ARCHIVE_MODE_OFF&&wal_level==WAL_LEVEL_MINIMAL)
@@ -5532,7 +5532,7 @@ int
55325532
MaxLivePostmasterChildren(void)
55335533
{
55345534
return2* (MaxConnections+autovacuum_max_workers+1+
5535-
max_worker_processes);
5535+
max_wal_senders+max_worker_processes);
55365536
}
55375537

55385538
/*

‎src/backend/replication/walsender.c

Lines changed: 4 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -2273,8 +2273,8 @@ InitWalSenderSlot(void)
22732273
Assert(MyWalSnd==NULL);
22742274

22752275
/*
2276-
* Find a free walsender slot and reserve it.If this fails, we must be
2277-
*out of WalSnd structures.
2276+
* Find a free walsender slot and reserve it.This must not fail due to
2277+
*the prior check for free WAL senders in InitProcess().
22782278
*/
22792279
for (i=0;i<max_wal_senders;i++)
22802280
{
@@ -2310,12 +2310,8 @@ InitWalSenderSlot(void)
23102310
break;
23112311
}
23122312
}
2313-
if (MyWalSnd==NULL)
2314-
ereport(FATAL,
2315-
(errcode(ERRCODE_TOO_MANY_CONNECTIONS),
2316-
errmsg("number of requested standby connections "
2317-
"exceeds max_wal_senders (currently %d)",
2318-
max_wal_senders)));
2313+
2314+
Assert(MyWalSnd!=NULL);
23192315

23202316
/* Arrange to clean up at walsender exit */
23212317
on_shmem_exit(WalSndKill,0);

‎src/backend/storage/lmgr/proc.c

Lines changed: 20 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -43,6 +43,7 @@
4343
#include"postmaster/autovacuum.h"
4444
#include"replication/slot.h"
4545
#include"replication/syncrep.h"
46+
#include"replication/walsender.h"
4647
#include"storage/condition_variable.h"
4748
#include"storage/standby.h"
4849
#include"storage/ipc.h"
@@ -147,8 +148,9 @@ ProcGlobalSemas(void)
147148
* running out when trying to start another backend is a common failure.
148149
* So, now we grab enough semaphores to support the desired max number
149150
* of backends immediately at initialization --- if the sysadmin has set
150-
* MaxConnections, max_worker_processes, or autovacuum_max_workers higher
151-
* than his kernel will support, he'll find out sooner rather than later.
151+
* MaxConnections, max_worker_processes, max_wal_senders, or
152+
* autovacuum_max_workers higher than his kernel will support, he'll
153+
* find out sooner rather than later.
152154
*
153155
* Another reason for creating semaphores here is that the semaphore
154156
* implementation typically requires us to create semaphores in the
@@ -180,6 +182,7 @@ InitProcGlobal(void)
180182
ProcGlobal->freeProcs=NULL;
181183
ProcGlobal->autovacFreeProcs=NULL;
182184
ProcGlobal->bgworkerFreeProcs=NULL;
185+
ProcGlobal->walsenderFreeProcs=NULL;
183186
ProcGlobal->startupProc=NULL;
184187
ProcGlobal->startupProcPid=0;
185188
ProcGlobal->startupBufferPinWaitBufId=-1;
@@ -253,13 +256,20 @@ InitProcGlobal(void)
253256
ProcGlobal->autovacFreeProcs=&procs[i];
254257
procs[i].procgloballist=&ProcGlobal->autovacFreeProcs;
255258
}
256-
elseif (i<MaxBackends)
259+
elseif (i<MaxConnections+autovacuum_max_workers+1+max_worker_processes)
257260
{
258261
/* PGPROC for bgworker, add to bgworkerFreeProcs list */
259262
procs[i].links.next= (SHM_QUEUE*)ProcGlobal->bgworkerFreeProcs;
260263
ProcGlobal->bgworkerFreeProcs=&procs[i];
261264
procs[i].procgloballist=&ProcGlobal->bgworkerFreeProcs;
262265
}
266+
elseif (i<MaxBackends)
267+
{
268+
/* PGPROC for walsender, add to walsenderFreeProcs list */
269+
procs[i].links.next= (SHM_QUEUE*)ProcGlobal->walsenderFreeProcs;
270+
ProcGlobal->walsenderFreeProcs=&procs[i];
271+
procs[i].procgloballist=&ProcGlobal->walsenderFreeProcs;
272+
}
263273

264274
/* Initialize myProcLocks[] shared memory queues. */
265275
for (j=0;j<NUM_LOCK_PARTITIONS;j++)
@@ -311,6 +321,8 @@ InitProcess(void)
311321
procgloballist=&ProcGlobal->autovacFreeProcs;
312322
elseif (IsBackgroundWorker)
313323
procgloballist=&ProcGlobal->bgworkerFreeProcs;
324+
elseif (am_walsender)
325+
procgloballist=&ProcGlobal->walsenderFreeProcs;
314326
else
315327
procgloballist=&ProcGlobal->freeProcs;
316328

@@ -341,6 +353,11 @@ InitProcess(void)
341353
* in the autovacuum case?
342354
*/
343355
SpinLockRelease(ProcStructLock);
356+
if (am_walsender)
357+
ereport(FATAL,
358+
(errcode(ERRCODE_TOO_MANY_CONNECTIONS),
359+
errmsg("number of requested standby connections exceeds max_wal_senders (currently %d)",
360+
max_wal_senders)));
344361
ereport(FATAL,
345362
(errcode(ERRCODE_TOO_MANY_CONNECTIONS),
346363
errmsg("sorry, too many clients already")));

‎src/backend/utils/init/postinit.c

Lines changed: 5 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -527,7 +527,7 @@ InitializeMaxBackends(void)
527527

528528
/* the extra unit accounts for the autovacuum launcher */
529529
MaxBackends=MaxConnections+autovacuum_max_workers+1+
530-
max_worker_processes;
530+
max_worker_processes+max_wal_senders;
531531

532532
/* internal error because the values were all checked previously */
533533
if (MaxBackends>MAX_BACKENDS)
@@ -811,12 +811,11 @@ InitPostgres(const char *in_dbname, Oid dboid, const char *username,
811811
}
812812

813813
/*
814-
* The last few connection slots are reserved for superusers. Although
815-
* replication connections currently require superuser privileges, we
816-
* don't allow them to consume the reserved slots, which are intended for
817-
* interactive use.
814+
* The last few connection slots are reserved for superusers. Replication
815+
* connections are drawn from slots reserved with max_wal_senders and not
816+
* limited by max_connections or superuser_reserved_connections.
818817
*/
819-
if ((!am_superuser||am_walsender)&&
818+
if (!am_superuser&& !am_walsender&&
820819
ReservedBackends>0&&
821820
!HaveNFreeProcs(ReservedBackends))
822821
ereport(FATAL,

‎src/backend/utils/misc/guc.c

Lines changed: 17 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -187,6 +187,7 @@ static const char *show_tcp_keepalives_count(void);
187187
staticboolcheck_maxconnections(int*newval,void**extra,GucSourcesource);
188188
staticboolcheck_max_worker_processes(int*newval,void**extra,GucSourcesource);
189189
staticboolcheck_autovacuum_max_workers(int*newval,void**extra,GucSourcesource);
190+
staticboolcheck_max_wal_senders(int*newval,void**extra,GucSourcesource);
190191
staticboolcheck_autovacuum_work_mem(int*newval,void**extra,GucSourcesource);
191192
staticboolcheck_effective_io_concurrency(int*newval,void**extra,GucSourcesource);
192193
staticvoidassign_effective_io_concurrency(intnewval,void*extra);
@@ -2090,7 +2091,7 @@ static struct config_int ConfigureNamesInt[] =
20902091
},
20912092

20922093
{
2093-
/* see max_connectionsand max_wal_senders*/
2094+
/* see max_connections */
20942095
{"superuser_reserved_connections",PGC_POSTMASTER,CONN_AUTH_SETTINGS,
20952096
gettext_noop("Sets the number of connection slots reserved for superusers."),
20962097
NULL
@@ -2608,14 +2609,13 @@ static struct config_int ConfigureNamesInt[] =
26082609
},
26092610

26102611
{
2611-
/* see max_connections and superuser_reserved_connections */
26122612
{"max_wal_senders",PGC_POSTMASTER,REPLICATION_SENDING,
26132613
gettext_noop("Sets the maximum number of simultaneously running WAL sender processes."),
26142614
NULL
26152615
},
26162616
&max_wal_senders,
26172617
10,0,MAX_BACKENDS,
2618-
NULL,NULL,NULL
2618+
check_max_wal_senders,NULL,NULL
26192619
},
26202620

26212621
{
@@ -10911,15 +10911,25 @@ static bool
1091110911
check_maxconnections(int*newval,void**extra,GucSourcesource)
1091210912
{
1091310913
if (*newval+autovacuum_max_workers+1+
10914-
max_worker_processes>MAX_BACKENDS)
10914+
max_worker_processes+max_wal_senders>MAX_BACKENDS)
1091510915
return false;
1091610916
return true;
1091710917
}
1091810918

1091910919
staticbool
1092010920
check_autovacuum_max_workers(int*newval,void**extra,GucSourcesource)
1092110921
{
10922-
if (MaxConnections+*newval+1+max_worker_processes>MAX_BACKENDS)
10922+
if (MaxConnections+*newval+1+
10923+
max_worker_processes+max_wal_senders>MAX_BACKENDS)
10924+
return false;
10925+
return true;
10926+
}
10927+
10928+
staticbool
10929+
check_max_wal_senders(int*newval,void**extra,GucSourcesource)
10930+
{
10931+
if (MaxConnections+autovacuum_max_workers+1+
10932+
max_worker_processes+*newval>MAX_BACKENDS)
1092310933
return false;
1092410934
return true;
1092510935
}
@@ -10950,7 +10960,8 @@ check_autovacuum_work_mem(int *newval, void **extra, GucSource source)
1095010960
staticbool
1095110961
check_max_worker_processes(int*newval,void**extra,GucSourcesource)
1095210962
{
10953-
if (MaxConnections+autovacuum_max_workers+1+*newval>MAX_BACKENDS)
10963+
if (MaxConnections+autovacuum_max_workers+1+
10964+
*newval+max_wal_senders>MAX_BACKENDS)
1095410965
return false;
1095510966
return true;
1095610967
}

‎src/bin/pg_controldata/pg_controldata.c

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -304,6 +304,8 @@ main(int argc, char *argv[])
304304
ControlFile->MaxConnections);
305305
printf(_("max_worker_processes setting: %d\n"),
306306
ControlFile->max_worker_processes);
307+
printf(_("max_wal_senders setting: %d\n"),
308+
ControlFile->max_wal_senders);
307309
printf(_("max_prepared_xacts setting: %d\n"),
308310
ControlFile->max_prepared_xacts);
309311
printf(_("max_locks_per_xact setting: %d\n"),

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