Thanks for your response. It’s Connection Timeout.
Some additional info - i just went ahead and for sake of trying updated the olcthread value to 1750 and post that was able to get 1650 concurrent connections working concurrently consistently, but anything beyond that again randomly threw connection timeout errors. 

Message sent from a mobile device, please excuse typos and brevity.

On Sep 13, 2021, at 9:28 PM, Howard Chu <> wrote: wrote:

Was load testing against openldap (slapd-meta) where we were trying to submit 1000 concurrent bind requests. This was done using the JMeter load testing tool. In every run approximately only 420-430 bind requests are successful and remaining 500+ bind requests fail with "Communication Exception" error. We also tried with 500 bind requests and the result was somewhat same - 420 odd successful and 70-80 failed with communication exception.

What does a "Communication exception" actually mean? Connection refused, connection timed out, what?

We've tested tens of thousands of concurrent connections with slapd. It is unlikely to be the problem here.

We have openldap 2.4.56 installed on a RHEL 8.1 host with 32GB memory and 8CPU. We have configured max open files for the slapd process to be 65K .

Our requirement is to support 6000 concurrent requests at minimum. Is there any configuration that can be tweaked to support this amount of concurrent load ? I do see "olcConcurrency" & "olcThreads" set to 0 and 16 respectively. Should we be tweaking these to support the required load, if yes what should be the values for those ? Please assist. Thank you for your help !

 -- Howard Chu
 CTO, Symas Corp. 
 Director, Highland Sun
 Chief Architect, OpenLDAP