Hello, 

I am using Monetdb as the query engine of an application currently in development. I am connecting to monetdb via a jdbc connection. 

I can easily reproduce a scenario where monetdb gets stuck on a query, and never complete execution.

Although reproducible, the issue is non deterministic, and it can occur while executing different queries, or not occur at all. 

When it happens I can see the thread stuck at 

I extracted the queries submitted to monetdb, and execute them via a standalone client (both the native client and a jdbc-based one) rather than our application, but I have been unable to reproduce the issue that way. I guess timing is important.

The problem still occur even when queries are submitted sequentially and setting gdk_nr_threads=1 and sql_optimizer=sequential_pipe.

The issue happens in Jul 2017-SP3 bugfix release (11.27.11), running on a Windows 7 machine. I have not tried 11.27.13, but by looking at the bug fixes I can't see anything relevant to this issue.

Is there something that I can try, or a way to gather more information about what is happening ?

I can share both the data, and the complete list of queries used during this scenario.

Thanks,