When DQP is enabled and all servers are participating in DQP there are some known problems you may encounter – When the multiplex coordinator participates in distributed query processing (DQP) under
stress conditions, the server may become unresponsive.If a query is using a table which was modified in the same transaction, and has uncommitted data, and if the worker nodes are heavily loaded, there is a small timing window in which the leader node may abort.
Workaround – To avoid these issues, Sybase recommends you create logical servers to control which servers within the multiplex can participate in DQP. Sybase recommends that the coordinator does not participate in DQP and is not a part of the logical server. In addition, do not run batch loads or transactions that deal with read-write operations like LOAD, INSERT, UPDATE or DELETE in IQ base tables on a logical server that contains more than one physical server. The write batches should run on a single physical machine. By ensuring that all your read-write transactions are done on a single server with the use of logical servers, you will not run the risk of hitting this timing window.
The issue can also be prevented by temporarily disabling DQP by calling set temporary option dqp_enabled= 'off' before starting your read-write transaction, or batch load, and setting it back to 'on' only after a commit or rollback.