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# Copyright (c) 2021-2025, PostgreSQL Global Development Group
# Test connection limits, i.e. max_connections, reserved_connections
# and superuser_reserved_connections.
use strict;
use warnings FATAL => 'all';
use PostgreSQL::Test::Cluster;
use PostgreSQL::Test::Utils;
use Test::More;
# Initialize the server with specific low connection limits
my $node = PostgreSQL::Test::Cluster->new('primary');
$node->init(
'auth_extra' => [
'--create-role', 'regress_regular,regress_reserved,regress_superuser'
]);
$node->append_conf('postgresql.conf', "max_connections = 6");
$node->append_conf('postgresql.conf', "reserved_connections = 2");
$node->append_conf('postgresql.conf', "superuser_reserved_connections = 1");
$node->append_conf('postgresql.conf', "log_connections = on");
$node->start;
$node->safe_psql(
'postgres', qq{
CREATE USER regress_regular LOGIN;
CREATE USER regress_reserved LOGIN;
GRANT pg_use_reserved_connections TO regress_reserved;
CREATE USER regress_superuser LOGIN SUPERUSER;
});
# With the limits we set in postgresql.conf, we can establish:
# - 3 connections for any user with no special privileges
# - 2 more connections for users belonging to "pg_use_reserved_connections"
# - 1 more connection for superuser
sub background_psql_as_user
{
my $user = shift;
return $node->background_psql(
'postgres',
on_error_die => 1,
extra_params => [ '-U', $user ]);
}
my @sessions = ();
my @raw_connections = ();
push(@sessions, background_psql_as_user('regress_regular'));
push(@sessions, background_psql_as_user('regress_regular'));
push(@sessions, background_psql_as_user('regress_regular'));
$node->connect_fails(
"dbname=postgres user=regress_regular",
"reserved_connections limit",
expected_stderr =>
qr/FATAL: remaining connection slots are reserved for roles with privileges of the "pg_use_reserved_connections" role/
);
push(@sessions, background_psql_as_user('regress_reserved'));
push(@sessions, background_psql_as_user('regress_reserved'));
$node->connect_fails(
"dbname=postgres user=regress_regular",
"reserved_connections limit",
expected_stderr =>
qr/FATAL: remaining connection slots are reserved for roles with the SUPERUSER attribute/
);
push(@sessions, background_psql_as_user('regress_superuser'));
$node->connect_fails(
"dbname=postgres user=regress_superuser",
"superuser_reserved_connections limit",
expected_stderr => qr/FATAL: sorry, too many clients already/);
# We can still open TCP (or Unix domain socket) connections, but
# beyond a certain number (roughly 2x max_connections), they will be
# "dead-end backends".
SKIP:
{
skip "this test requires working raw_connect()"
unless $node->raw_connect_works();
for (my $i = 0; $i <= 20; $i++)
{
my $sock = $node->raw_connect();
# On a busy system, the server might reject connections if
# postmaster cannot accept() them fast enough. The exact limit
# and behavior depends on the platform. To make this reliable,
# we attempt SSL negotiation on each connection before opening
# next one. The server will reject the SSL negotiations, but
# when it does so, we know that the backend has been launched
# and we should be able to open another connection.
# SSLRequest packet consists of packet length followed by
# NEGOTIATE_SSL_CODE.
my $negotiate_ssl_code = pack("Nnn", 8, 1234, 5679);
my $sent = $sock->send($negotiate_ssl_code);
# Read reply. We expect the server to reject it with 'N'
my $reply = "";
$sock->recv($reply, 1);
is($reply, "N", "dead-end connection $i");
push(@raw_connections, $sock);
}
}
# TODO: test that query cancellation is still possible. A dead-end
# backend can process a query cancellation packet.
# Clean up
foreach my $session (@sessions)
{
$session->quit;
}
foreach my $socket (@raw_connections)
{
$socket->close();
}
done_testing();
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