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authorTom Lane <tgl@sss.pgh.pa.us>2018-03-08 11:25:26 -0500
committerTom Lane <tgl@sss.pgh.pa.us>2018-03-08 11:25:26 -0500
commit4e0c743c18bf5435a4850510c5c74b3521c3e1e5 (patch)
tree548ba5c052c971a450f9f0bc5db10521b9946a69
parentf9f8784c8b3050aaec52da88a6e41b3e3f576b96 (diff)
downloadpostgresql-4e0c743c18bf5435a4850510c5c74b3521c3e1e5.tar.gz
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Fix cross-checking of ReservedBackends/max_wal_senders/MaxConnections.
We were independently checking ReservedBackends < MaxConnections and max_wal_senders < MaxConnections, but because walsenders aren't allowed to use superuser-reserved connections, that's really the wrong thing. Correct behavior is to insist on ReservedBackends + max_wal_senders being less than MaxConnections. Fix the code and associated documentation. This has been wrong for a long time, but since the situation probably hardly ever arises in the field (especially pre-v10, when the default for max_wal_senders was zero), no back-patch. Discussion: https://postgr.es/m/28271.1520195491@sss.pgh.pa.us
-rw-r--r--doc/src/sgml/config.sgml23
-rw-r--r--src/backend/postmaster/postmaster.c15
-rw-r--r--src/backend/utils/init/postinit.c2
-rw-r--r--src/backend/utils/misc/guc.c5
4 files changed, 24 insertions, 21 deletions
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 259a2d83b4a..3a8fc7d803c 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -696,8 +696,9 @@ include_dir 'conf.d'
<para>
The default value is three connections. The value must be less
- than the value of <varname>max_connections</varname>. This
- parameter can only be set at server start.
+ than <varname>max_connections</varname> minus
+ <xref linkend="guc-max-wal-senders"/>.
+ This parameter can only be set at server start.
</para>
</listitem>
</varlistentry>
@@ -2982,13 +2983,16 @@ include_dir 'conf.d'
maximum number of simultaneously running WAL sender
processes). The default is 10. The value 0 means replication is
disabled. WAL sender processes count towards the total number
- of connections, so the parameter cannot be set higher than
- <xref linkend="guc-max-connections"/>. Abrupt streaming client
- disconnection might cause an orphaned connection slot until
+ of connections, so this parameter's value must be less than
+ <xref linkend="guc-max-connections"/> minus
+ <xref linkend="guc-superuser-reserved-connections"/>.
+ Abrupt streaming client disconnection might leave an orphaned
+ connection slot behind until
a timeout is reached, so this parameter should be set slightly
higher than the maximum number of expected clients so disconnected
clients can immediately reconnect. This parameter can only
- be set at server start. <varname>wal_level</varname> must be set to
+ be set at server start.
+ Also, <varname>wal_level</varname> must be set to
<literal>replica</literal> or higher to allow connections from standby
servers.
</para>
@@ -3007,10 +3011,11 @@ include_dir 'conf.d'
(see <xref linkend="streaming-replication-slots"/>) that the server
can support. The default is 10. This parameter can only be set at
server start.
- <varname>wal_level</varname> must be set
- to <literal>replica</literal> or higher to allow replication slots to
- be used. Setting it to a lower value than the number of currently
+ Setting it to a lower value than the number of currently
existing replication slots will prevent the server from starting.
+ Also, <varname>wal_level</varname> must be set
+ to <literal>replica</literal> or higher to allow replication slots to
+ be used.
</para>
</listitem>
</varlistentry>
diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index f3ddf828bbe..660f3185e6b 100644
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -202,9 +202,9 @@ char *ListenAddresses;
/*
* ReservedBackends is the number of backends reserved for superuser use.
- * This number is taken out of the pool size given by MaxBackends so
+ * This number is taken out of the pool size given by MaxConnections so
* number of backend slots available to non-superusers is
- * (MaxBackends - ReservedBackends). Note what this really means is
+ * (MaxConnections - ReservedBackends). Note what this really means is
* "if there are <= ReservedBackends connections available, only superusers
* can make new connections" --- pre-existing superuser connections don't
* count against the limit.
@@ -882,14 +882,11 @@ PostmasterMain(int argc, char *argv[])
/*
* Check for invalid combinations of GUC settings.
*/
- if (ReservedBackends >= MaxConnections)
+ if (ReservedBackends + max_wal_senders >= MaxConnections)
{
- write_stderr("%s: superuser_reserved_connections must be less than max_connections\n", progname);
- ExitPostmaster(1);
- }
- if (max_wal_senders >= MaxConnections)
- {
- write_stderr("%s: max_wal_senders must be less than max_connections\n", progname);
+ write_stderr("%s: superuser_reserved_connections (%d) plus max_wal_senders (%d) must be less than max_connections (%d)\n",
+ progname,
+ ReservedBackends, max_wal_senders, MaxConnections);
ExitPostmaster(1);
}
if (XLogArchiveMode > ARCHIVE_MODE_OFF && wal_level == WAL_LEVEL_MINIMAL)
diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c
index 484628987f4..d8f45b3c43f 100644
--- a/src/backend/utils/init/postinit.c
+++ b/src/backend/utils/init/postinit.c
@@ -778,7 +778,7 @@ InitPostgres(const char *in_dbname, Oid dboid, const char *username,
}
/*
- * The last few connections slots are reserved for superusers. Although
+ * The last few connection slots are reserved for superusers. Although
* replication connections currently require superuser privileges, we
* don't allow them to consume the reserved slots, which are intended for
* interactive use.
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 0c4cc9160d4..a4f9b3668e0 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -1873,6 +1873,7 @@ static struct config_int ConfigureNamesInt[] =
},
{
+ /* see max_connections and max_wal_senders */
{"superuser_reserved_connections", PGC_POSTMASTER, CONN_AUTH_SETTINGS,
gettext_noop("Sets the number of connection slots reserved for superusers."),
NULL
@@ -2375,7 +2376,7 @@ static struct config_int ConfigureNamesInt[] =
},
{
- /* see max_connections */
+ /* see max_connections and superuser_reserved_connections */
{"max_wal_senders", PGC_POSTMASTER, REPLICATION_SENDING,
gettext_noop("Sets the maximum number of simultaneously running WAL sender processes."),
NULL
@@ -2386,7 +2387,7 @@ static struct config_int ConfigureNamesInt[] =
},
{
- /* see max_connections */
+ /* see max_wal_senders */
{"max_replication_slots", PGC_POSTMASTER, REPLICATION_SENDING,
gettext_noop("Sets the maximum number of simultaneously defined replication slots."),
NULL