David,
> 2. amavisd-milter requires to use Unix domain sockets to communicate
> with amavisd. This is not really a problem except that when I was
> stress-testing my test setup with 10 backend amavisd processes, I
> noticed that, once in a while, amavisd-milter was getting a
> "Connection refused" on the socket.
>
> The problem is that even though I properly limited the number of
> amavisd connections in amavisd-milter, amavisd does have a listen
> backlog (queuing of connecting clients) of maximum 5 clients. That
> is, if I have configured to use at most 10 amavisd processes and by
> chance 6 amavisd-milter processes try to establish a connection
> simultaneously, it will fail.
I don't see why it would be 5. The program flow goes like:
amavisd leaves Net::Server's option 'listen' at a default.
Net::Server.pm turns undef into 128:
$prop->{listen} = Socket::SOMAXCONN()
unless defined($prop->{listen}) && $prop->{listen} =~ /^\d{1,3}$/;
Net::Server::Proto::Unix.pm:
if( $unix_type != SOCK_DGRAM ){
$args{Listen} = $prop->{listen}; # how many connections for kernel to queue
}
Inserting a debug printout for $lport into IO::Socket::UNIX.pm like:
if(exists $arg->{Listen} && $type != SOCK_DGRAM) {
printf STDERR ("HERE: %s\n", $arg->{Listen});
$sock->listen($arg->{Listen} || 5) or
return undef;
}
and starting 'amavisd foreground' gives me 128, the same as for INET sockets.
> That's why, it would be useful to have in amavisd a variable called
> $listen_backlog or something like that, which would allow you to
> specify the queue size for the listen sockets. amavisd would then
> just need to pass this as 'listen' parameter to Net::Server...
--- amavisd.orig Wed Jun 27 12:43:00 2007
+++ amavisd Fri Jul 27 17:48:57 2007
@@ -282,5 +282,5 @@
$child_timeout $smtpd_timeout
%current_policy_bank %policy_bank %interface_policy
- $unix_socketname $inet_socket_port $inet_socket_bind
+ $unix_socketname $inet_socket_port $inet_socket_bind $listen_queue_size
$relayhost_is_client $smtpd_recipient_limit
$enforce_smtpd_message_size_limit_64kb_min
@@ -11444,4 +11444,5 @@
host => (!defined($inet_socket_bind) || $inet_socket_bind eq '' ? '*'
: $inet_socket_bind),
+ listen => defined $listen_queue_size ? $listen_queue_size : undef,
max_servers => defined $max_servers_override ? $max_servers_override
: $max_servers, # number of pre-forked children
Unfortunately Net::Server does not allow to specify listen backlog queue size
individually for each socket.
> Note that this is also not really an issue with inet sockets because
> of the way connections to inet sockets are handled: if there is no
> free space in the connection queue, the SYN packet is just dropped
> so that the client comes back later. With unix sockets, it is not
> possible to do that so the client gets immediately a connection
> refused.
'netstat -L -a' is showing me 128 for all amavisd sockets.
Mark
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