Summary

If MarkLogic Server is installed on an Amazon Elastic Compute Cloud (EC2) instance and you execute queries in the MarkLogic Query Console, it is possible that the queries will be silently cancelled. Long running queries may time out because of an AWS attached Load Balancer.

Details,

The Amazon Elastic Load Balancer (ELB) performs health check on running instances using protocols, timeouts etc.  The ELB terminates a connection if it is idle for more than 60 seconds. An idle connection is established when there is no action or event performed i.e. read or write. Consequently, when queries run for more than 60 seconds, the load balancer will think the connection is idle and will terminate it. When the ELB terminates a Query Console connection, it does not give any message in the display. Instead, an “XDMP-CANCELLED” message is logged to the MarkLogic ErrorLog.txt file. An XDMP-CANCELLED message indicates that query was cancelled either explicitly or as a result of a system event.

Removing the Load balancer from your EC2 instance is one solutions to enable long running Query Console queries on an Amazon EC2 instance.

[ref: http://docs.aws.amazon.com/ElasticLoadBalancing/latest/DeveloperGuide/ts-elb-healthcheck.html]