How to optimise Percona MongoDB LDAP for more concurrent connections? - mongodb

Question

Percona MongoDB with LDAP is not working for more than 2 concurrent threads even if the connection pool configured for more than 2.
MongoDB Configuration,
setParameter:
saslauthdPath: /app/mongo/mongoldap/var/run/saslauthd/mux
authenticationMechanisms: PLAIN,SCRAM-SHA-1
ldapConnectionPoolSizePerHost: 10
ldapUseConnectionPool: true
ldapDebug: true
SASL Configuration,
ldap_servers: ldap://ldap.forumsys.com
ldap_mech: PLAIN
ldap_search_base: dc=example,dc=com
ldap_filter: (cn=%u)
ldap_bind_dn: cn=read-only-admin,dc=example,dc=com
ldap_password: password
Test Script (PHP),
<?php
use MongoDB\Driver\Manager as MongoDB;
use MongoDB\Driver\Query as Query;
use MongoDB\Driver\BulkWrite as BulkWrite;
try{
for($i=0;$i<3;$i++){
$handlerName = "handle".$i;
$$handlerName = new MongoDB("mongodb://xx.xx.xx.xx",array("authSource"=>"$external","authMechanism"=>"PLAIN","username"=>"cn=read-only-admin,dc=example,dc=com","password"=>"password","tls"=>true,"tlsCertificateKeyFile"=>"/xyzabc/dbs/mongoclient.pem","tlsCAFile"=>"/xyzabc/dbs/mongoca.pem","tlsAllowInvalidCertificates"=>true));
$filters=array();
$options=array();
$command = new Query($filters,$options);
$query="xyzabc.customerdetails";
$result = $$handlerName->executeQuery($query,$command);
$resultAsJson = $result->toArray();
$resultAsArray = json_decode(json_encode($resultAsJson), True);
print_r(count($resultAsArray));
echo "\n";
sleep(5);
}
for($i=0;$i<3;$i++){
$handlerName = "handle".$i;
$query="xyzabc.client";
$result = $$handlerName->executeQuery($query,$command);
$resultAsJson = $result->toArray();
$resultAsArray = json_decode(json_encode($resultAsJson), True);
print_r(count($resultAsArray));
echo "\n";
}
echo "Success";
}catch(Exception $e){
print_r($e);
echo "Failed";
}
?>
Test Script (Shell script for nohup),
nohup php test.php > output1.log 2>&1 &
nohup php test.php > output2.log 2>&1 &
nohup php test.php > output3.log 2>&1 &
nohup php test.php > output4.log 2>&1 &
nohup php test.php > output5.log 2>&1 &
Test Results,
Script executed in a single thread (same process ID) - there is no error it works for any number of connections
If the same script is executed on nohup (multi-thread or multiple process IDs) - only works for the first two threads, fails for 3rd and above
Error Message (MongoDB log),
LDAPLibraryError: Failed to authenticate 'cn=read-only-admin,dc=example,dc=com' using simple bind; LDAP error: Can't contact LDAP server
Percona MongoDB Version: 4.4.2-4
When the test PHP script is executed synchronously there is no error with the number of connections. I assume this is because the process ID is the same for all the DB connections so it uses the same connection pool.
On the other hand, if it is executed concurrently (with nohup), only the first 2 connections are working, by this, I assume only the first 2 connection pools are working and from 3rd connection pool, the requests are failing.
Since I have ldapConnectionPoolSizePerHost is set to 10, I don't understand why this is not working as expected.
Thanks in advance!