From 2961ebbeb1e2910752fa4297f6aaa52492b30741 Mon Sep 17 00:00:00 2001 From: Nathan Bossart Date: Tue, 17 Jan 2023 15:36:59 -0800 Subject: [PATCH v1 2/2] Introduce reserved_connections and pg_use_reserved_connections. This provides a way to reserve connection slots for non-superusers. superuser_reserved_connections remains as a final reserve in case reserved_connections has been exhausted. --- doc/src/sgml/config.sgml | 40 +++++++++++++++++-- doc/src/sgml/user-manag.sgml | 5 +++ src/backend/postmaster/postmaster.c | 28 ++++++++----- src/backend/utils/init/postinit.c | 16 ++++++-- src/backend/utils/misc/guc_tables.c | 11 +++++ src/backend/utils/misc/postgresql.conf.sample | 1 + src/include/catalog/pg_authid.dat | 5 +++ src/include/postmaster/postmaster.h | 1 + 8 files changed, 92 insertions(+), 15 deletions(-) diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml index 89d53f2a64..aa100870b9 100644 --- a/doc/src/sgml/config.sgml +++ b/doc/src/sgml/config.sgml @@ -725,18 +725,52 @@ include_dir 'conf.d' number of active concurrent connections is at least max_connections minus superuser_reserved_connections, new - connections will be accepted only for superusers, and no - new replication connections will be accepted. + connections will be accepted only for superusers. The connection slots + reserved by this parameter are intended as final reserve for emergency + use after the slots reserved by + have been exhausted. The default value is three connections. The value must be less - than max_connections. + than max_connections minus + reserved_connections. This parameter can only be set at server start. + + reserved_connections (integer) + + reserved_connections configuration parameter + + + + + Determines the number of connection slots that are + reserved for connections by roles with privileges of the + pg_used_reserved_connections + role. Whenever the number of free connection slots is greater than + but less than or + equal to the sum of superuser_reserved_connections + and reserved_connections, new connections will be + accepted only for superusers and roles with privileges of + pg_use_reserved_connections. If + superuser_reserved_connections or fewer connection + slots are available, new connections will be accepted only for + superusers. + + + + The default value is three connections. The value must be less than + max_connections minus + superuser_reserved_connections. This parameter can + only be set at server start. + + + + unix_socket_directories (string) diff --git a/doc/src/sgml/user-manag.sgml b/doc/src/sgml/user-manag.sgml index 71a2d8f298..d553b1adab 100644 --- a/doc/src/sgml/user-manag.sgml +++ b/doc/src/sgml/user-manag.sgml @@ -689,6 +689,11 @@ DROP ROLE doomed_role; and LOCK TABLE on all relations. + + pg_use_reserved_backends + Allow use of connection slots reserved via + . + diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c index 470704f364..ac69d3fd9b 100644 --- a/src/backend/postmaster/postmaster.c +++ b/src/backend/postmaster/postmaster.c @@ -205,14 +205,23 @@ char *ListenAddresses; /* * SuperuserReservedBackends is the number of backends reserved for superuser - * use. This number is taken out of the pool size given by MaxConnections so - * number of backend slots available to non-superusers is - * (MaxConnections - SuperuserReservedBackends). Note what this really means - * is "if there are <= SuperuserReservedBackends connections available, only - * superusers can make new connections" --- pre-existing superuser connections - * don't count against the limit. + * use, and ReservedBackends is the number of backends reserved for use by + * roles with privileges of the pg_use_reserved_backends predefined role. + * These are taken out of the pool of MaxConnections backend slots, so the + * number of backend slots available for roles that are neither superuser nor + * have privileges of pg_use_reserved_backends is + * (MaxConnections - SuperuserReservedBackends - ReservedBackends). + * + * If the number of remaining slots is less than or equal to + * SuperuserReservedBackends, only superusers can make new connections. If the + * number of remaining slots is greater than SuperuserReservedBackends but less + * than or equal to (SuperuserReservedBackends + ReservedBackends), only + * superusers and roles with privileges of pg_use_reserved_backends can make + * new connections. Note that pre-existing superuser and + * pg_use_reserved_backends connections don't count against the limits. */ int SuperuserReservedBackends; +int ReservedBackends; /* The socket(s) we're listening to. */ #define MAXLISTEN 64 @@ -908,11 +917,12 @@ PostmasterMain(int argc, char *argv[]) /* * Check for invalid combinations of GUC settings. */ - if (SuperuserReservedBackends >= MaxConnections) + if (SuperuserReservedBackends + ReservedBackends >= MaxConnections) { - write_stderr("%s: superuser_reserved_connections (%d) must be less than max_connections (%d)\n", + write_stderr("%s: superuser_reserved_connections (%d) plus reserved_connections (%d) must be less than max_connections (%d)\n", progname, - SuperuserReservedBackends, MaxConnections); + SuperuserReservedBackends, ReservedBackends, + 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 6fa696fe8d..4e74cdbb9e 100644 --- a/src/backend/utils/init/postinit.c +++ b/src/backend/utils/init/postinit.c @@ -922,9 +922,11 @@ InitPostgres(const char *in_dbname, Oid dboid, } /* - * The last few connection slots are reserved for superusers. Replication - * connections are drawn from slots reserved with max_wal_senders and not - * limited by max_connections or superuser_reserved_connections. + * The last few connection slots are reserved for superusers and roles with + * privileges of pg_use_reserved_connections. Replication connections are + * drawn from slots reserved with max_wal_senders and are not limited by + * max_connections, superuser_reserved_connections, or + * reserved_connections. */ if (!am_superuser && !am_walsender && SuperuserReservedBackends > 0 && @@ -933,6 +935,14 @@ InitPostgres(const char *in_dbname, Oid dboid, (errcode(ERRCODE_TOO_MANY_CONNECTIONS), errmsg("remaining connection slots are reserved for non-replication superuser connections"))); + if (!has_privs_of_role(GetUserId(), ROLE_PG_USE_RESERVED_CONNECTIONS) && + !am_walsender && + ReservedBackends > 0 && + !HaveNFreeProcs(SuperuserReservedBackends + ReservedBackends)) + ereport(FATAL, + (errcode(ERRCODE_TOO_MANY_CONNECTIONS), + errmsg("remaining connection slots are reserved for roles with privileges of pg_use_reserved_backends"))); + /* Check replication permissions needed for walsender processes. */ if (am_walsender) { diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c index 5aa2cda8f9..1e94e70b42 100644 --- a/src/backend/utils/misc/guc_tables.c +++ b/src/backend/utils/misc/guc_tables.c @@ -2168,6 +2168,17 @@ struct config_int ConfigureNamesInt[] = NULL, NULL, NULL }, + { + {"reserved_connections", PGC_POSTMASTER, CONN_AUTH_SETTINGS, + gettext_noop("Sets the number of connection slots reserved for roles " + "with privileges of pg_use_reserved_connections."), + NULL + }, + &ReservedBackends, + 3, 0, MAX_BACKENDS, + NULL, NULL, NULL + }, + { {"min_dynamic_shared_memory", PGC_POSTMASTER, RESOURCES_MEM, gettext_noop("Amount of dynamic shared memory reserved at startup."), diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample index 4cceda4162..5107afe140 100644 --- a/src/backend/utils/misc/postgresql.conf.sample +++ b/src/backend/utils/misc/postgresql.conf.sample @@ -64,6 +64,7 @@ #port = 5432 # (change requires restart) #max_connections = 100 # (change requires restart) #superuser_reserved_connections = 3 # (change requires restart) +#reserved_connections = 3 # (change requires restart) #unix_socket_directories = '/tmp' # comma-separated list of directories # (change requires restart) #unix_socket_group = '' # (change requires restart) diff --git a/src/include/catalog/pg_authid.dat b/src/include/catalog/pg_authid.dat index 2a2fee7d28..f2e5663c9f 100644 --- a/src/include/catalog/pg_authid.dat +++ b/src/include/catalog/pg_authid.dat @@ -89,5 +89,10 @@ rolcreaterole => 'f', rolcreatedb => 'f', rolcanlogin => 'f', rolreplication => 'f', rolbypassrls => 'f', rolconnlimit => '-1', rolpassword => '_null_', rolvaliduntil => '_null_' }, +{ oid => '4550', oid_symbol => 'ROLE_PG_USE_RESERVED_CONNECTIONS', + rolname => 'pg_use_reserved_connections', rolsuper => 'f', rolinherit => 't', + rolcreaterole => 'f', rolcreatedb => 'f', rolcanlogin => 'f', + rolreplication => 'f', rolbypassrls => 'f', rolconnlimit => '-1', + rolpassword => '_null_', rolvaliduntil => '_null_' }, ] diff --git a/src/include/postmaster/postmaster.h b/src/include/postmaster/postmaster.h index 168d85a3d1..18ef5afa75 100644 --- a/src/include/postmaster/postmaster.h +++ b/src/include/postmaster/postmaster.h @@ -16,6 +16,7 @@ /* GUC options */ extern PGDLLIMPORT bool EnableSSL; extern PGDLLIMPORT int SuperuserReservedBackends; +extern PGDLLIMPORT int ReservedBackends; extern PGDLLIMPORT int PostPortNumber; extern PGDLLIMPORT int Unix_socket_permissions; extern PGDLLIMPORT char *Unix_socket_group; -- 2.25.1