hello together,
im experiencing weird timeouts from mongodb or the perl driver, but i guess its the server. i already tried to debug and track down whats happening(also searched the perl driver for any occurence of this timeout)

it seems its some hardcoded 20 second timeout..

i got to this conclusion through my scripts.. they end up like this:

[Thu Oct 25 01:26:57 2018] update_one @ collection foo..
MongoDB::WriteError: Write results unavailable from 192.168.91.187:5000 due to Couldn't get a connection within the time limit
script exit at: Don Okt 25 01:27:18 CEST 2018

and that works exactly like this:

print "[" . scalar localtime . "] collection (foo)..\n";
my $col=$con->get_database("foo")->get_collection("foo");

print "[" . scalar localtime . "] update_one @ collection foo..\n";
$col->update_one({"foo" => foo},{'$addToSet' => { "foo" => foo }}); <= kills the script

so the difference between the update call and the script exit is everytime 20 seconds..

it happens not only with addtoset.

i already connect to the the server with very high timeout values (for exact this debug purpose):

$con= MongoDB::MongoClient->new(
host => $constr,
connect_timeout_ms => 1000 * 60 * 10, #10 minutes
max_time_ms => 1000 * 60 * 60 * 3, #3 hours (max time for operation)
server_selection_timeout_ms => 1000 * 60 * 60 * 1, #1 hour
socket_timeout_ms => 1000 * 60 * 60 * 4, #4 hours (wait for reply)
server_selection_try_once => 0,
w => 1,
wtimeout => 1000 * 60 * 60 * 1, #1 hour
j => 0 );

so the question is, where does this timeout come from and what can i do, except from try/catch to prevent these errors?

im using MongoDB 3.6.5, and the Perl Driver 2.0.1 at Debian Stable.

kind regards,
Michael