This behavior is usually related to different types of constraints at the data source. It could be due to inserting duplicate values in the same index, concurrency limits and order of transactions to name a few. [Greenplum Deadlock Detection with Resource Queue]( https://community.pivotal.io/s/article/Greenplum-Deadlock-Detection-with-Resource-Queue) gives some information about how the situation works behind the scenes.
I suggest you execute the query through another client to check if the issue persists. If it does, you need to figure out how to fine tune your query to make sure that PostGres does not enter in deadlock situation.
In Denodo terms, it could either mean:
1. Rearranging the query
2. Changing the join type. You can refer to [Optimizing Join Operations]( https://community.denodo.com/docs/html/browse/7.0/vdp/administration/optimizing_queries/optimizing_join_operations/optimizing_join_operations) for more details
3. Prohibitting simultaneous query executions
Since this has to be seen on a case by case basis, I suggest that if you are a Denodo customer, you should open a support case if you have a valid support account, so that the views and logs can be analyzed to check what is causing this contention and how each use case needs to be addressed.
Hope this helps!