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If you have high volumes of flows you should DISABLE DNS lookup, change 'opflow_resolve_endpoint_dns' => 'true', to false in /usr/local/omk/conf/opCommon.nmis to speed up performance. Each of the opflow processes will have to wait for each of the DNS lookups which means you will have a large number number processes waiting for DNS to return information. This is especially true on internet traffic as resolution will require a PTR lookup through to the SOA for that IP which could take a while.