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/exchange/ExchangeService.java
@Override
        public void messageReceived(OpenExchangeRequest request, TransportChannel channel, Task task) throws Exception {
            createSinkHandler(request.sessionId, request.exchangeBuffer);
            channel.sendResponse(new TransportResponse.Empty());
        }
    }
    private class ExchangeTransportAction implements TransportRequestHandler<ExchangeRequest> {
        @Override
        public void messageReceived(ExchangeRequest request, TransportChannel channel, Task task) {
            final String exchangeId = request.exchangeId();
            ActionListener<ExchangeResponse> listener = new ChannelActionListener<>(channel);
            final ExchangeSinkHandler sinkHandler = sinks.get(exchangeId);
            if (sinkHandler == null) {
                listener.onResponse(new ExchangeResponse(null, true));
            } else {
                
                if (sinkHandler.hasData() == false) {
                    ((CancellableTask) task).addListener(() -> sinkHandler.onFailure(new TaskCancelledException("task cancelled")));
                }
                sinkHandler.fetchPageAsync(request.sourcesFinished(), listener);
            }
        }
    }
    private final class InactiveSinksReaper extends AbstractAsyncTask {