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
if (parentTaskId.isSet() == false) {
                assert false : "DriverRequest must have a parent task";
                throw new IllegalStateException("DriverRequest must have a parent task");
            }
            return new CancellableTask(id, type, action, "", parentTaskId, headers) {
                @Override
                protected void onCancelled() {
                    String reason = Objects.requireNonNullElse(getReasonCancelled(), "cancelled");
                    driver.cancel(reason);
                }
                @Override
                public String getDescription() {
                    return driver.describe();
                }
                @Override
                public Status getStatus() {
                    return driver.status();
                }
            };
        }
    }
    private record DriverRequestHandler(Executor executor) implements TransportRequestHandler<DriverRequest> {
        @Override
        public void messageReceived(DriverRequest request, TransportChannel channel, Task task) {
            var listener = new ChannelActionListener<TransportResponse.Empty>(channel);
            Driver.start(executor, request.driver, Driver.DEFAULT_MAX_ITERATIONS, listener.map(unused -> TransportResponse.Empty.INSTANCE));
        }
    }
}