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mirror of https://github.com/postgres/postgres.git synced 2025-07-15 19:21:59 +03:00

Move max_wal_senders out of max_connections for connection slot handling

Since its introduction, max_wal_senders is counted as part of
max_connections when it comes to define how many connection slots can be
used for replication connections with a WAL sender context.  This can
lead to confusion for some users, as it could be possible to block a
base backup or replication from happening because other backend sessions
are already taken for other purposes by an application, and
superuser-only connection slots are not a correct solution to handle
that case.

This commit makes max_wal_senders independent of max_connections for its
handling of PGPROC entries in ProcGlobal, meaning that connection slots
for WAL senders are handled using their own free queue, like autovacuum
workers and bgworkers.

One compatibility issue that this change creates is that a standby now
requires to have a value of max_wal_senders at least equal to its
primary.  So, if a standby created enforces the value of
max_wal_senders to be lower than that, then this could break failovers.
Normally this should not be an issue though, as any settings of a
standby are inherited from its primary as postgresql.conf gets normally
copied as part of a base backup, so parameters would be consistent.

Author: Alexander Kukushkin
Reviewed-by: Kyotaro Horiguchi, Petr Jelínek, Masahiko Sawada, Oleksii
Kliukin
Discussion: https://postgr.es/m/CAFh8B=nBzHQeYAu0b8fjK-AF1X4+_p6GRtwG+cCgs6Vci2uRuQ@mail.gmail.com
This commit is contained in:
Michael Paquier
2019-02-12 10:07:56 +09:00
parent 1d92a0c9f7
commit ea92368cd1
15 changed files with 100 additions and 55 deletions

View File

@ -187,6 +187,7 @@ static const char *show_tcp_keepalives_count(void);
static bool check_maxconnections(int *newval, void **extra, GucSource source);
static bool check_max_worker_processes(int *newval, void **extra, GucSource source);
static bool check_autovacuum_max_workers(int *newval, void **extra, GucSource source);
static bool check_max_wal_senders(int *newval, void **extra, GucSource source);
static bool check_autovacuum_work_mem(int *newval, void **extra, GucSource source);
static bool check_effective_io_concurrency(int *newval, void **extra, GucSource source);
static void assign_effective_io_concurrency(int newval, void *extra);
@ -2090,7 +2091,7 @@ static struct config_int ConfigureNamesInt[] =
},
{
/* see max_connections and max_wal_senders */
/* see max_connections */
{"superuser_reserved_connections", PGC_POSTMASTER, CONN_AUTH_SETTINGS,
gettext_noop("Sets the number of connection slots reserved for superusers."),
NULL
@ -2608,14 +2609,13 @@ static struct config_int ConfigureNamesInt[] =
},
{
/* 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
},
&max_wal_senders,
10, 0, MAX_BACKENDS,
NULL, NULL, NULL
check_max_wal_senders, NULL, NULL
},
{
@ -10911,7 +10911,7 @@ static bool
check_maxconnections(int *newval, void **extra, GucSource source)
{
if (*newval + autovacuum_max_workers + 1 +
max_worker_processes > MAX_BACKENDS)
max_worker_processes + max_wal_senders > MAX_BACKENDS)
return false;
return true;
}
@ -10919,7 +10919,17 @@ check_maxconnections(int *newval, void **extra, GucSource source)
static bool
check_autovacuum_max_workers(int *newval, void **extra, GucSource source)
{
if (MaxConnections + *newval + 1 + max_worker_processes > MAX_BACKENDS)
if (MaxConnections + *newval + 1 +
max_worker_processes + max_wal_senders > MAX_BACKENDS)
return false;
return true;
}
static bool
check_max_wal_senders(int *newval, void **extra, GucSource source)
{
if (MaxConnections + autovacuum_max_workers + 1 +
max_worker_processes + *newval > MAX_BACKENDS)
return false;
return true;
}
@ -10950,7 +10960,8 @@ check_autovacuum_work_mem(int *newval, void **extra, GucSource source)
static bool
check_max_worker_processes(int *newval, void **extra, GucSource source)
{
if (MaxConnections + autovacuum_max_workers + 1 + *newval > MAX_BACKENDS)
if (MaxConnections + autovacuum_max_workers + 1 +
*newval + max_wal_senders > MAX_BACKENDS)
return false;
return true;
}