Performing any long running task or CPU intensive work on transport_worker threads is problematic. This is typically very bad for cluster stability.

This issue has been filed to examine the usage of transport_worked threads by ESQL, with the intention of "offloading" as much as possible, including deserialising large(ish) amounts of data.
x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/operator/DriverTaskRunner.java
private final Driver driver;
        DriverRequest(Driver driver) {
            this.driver = driver;
        }
        DriverRequest(StreamInput in) {
            throw new UnsupportedOperationException("Driver request should never leave the current node");
        }
        @Override
        public void writeTo(StreamOutput out) throws IOException {
            throw new UnsupportedOperationException("Driver request should never leave the current node");
        }
        @Override
        public ActionRequestValidationException validate() {
            return null;
        }
        @Override
        public Task createTask(long id, String type, String action, TaskId parentTaskId, Map<String, String> headers) {