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/test/java/org/elasticsearch/compute/operator/exchange/ExchangeServiceTests.java
@Override
            public void messageReceived(
                TransportRequestHandler<TransportRequest> handler,
                TransportRequest request,
                TransportChannel channel,
                Task task
            ) throws Exception {
                FilterTransportChannel filterChannel = new FilterTransportChannel(channel) {
                    @Override
                    public void sendResponse(TransportResponse response) throws IOException {
                        ExchangeResponse exchangeResponse = (ExchangeResponse) response;
                        if (exchangeResponse.page() != null) {
                            IntBlock block = exchangeResponse.page().getBlock(0);
                            for (int i = 0; i < block.getPositionCount(); i++) {
                                if (block.getInt(i) == disconnectOnSeqNo) {
                                    throw new IOException("page is too large");
                                }
                            }
                        }
                        super.sendResponse(response);
                    }
                };
                handler.messageReceived(request, filterChannel, task);
            }
        });
        try (exchange0; exchange1; node0; node1) {
            String exchangeId = "exchange";
            Task task = new Task(1, "", "", "", null, Collections.emptyMap());
            ExchangeSourceHandler sourceHandler = exchange0.createSourceHandler(exchangeId, randomIntBetween(1, 128), ESQL_TEST_EXECUTOR);
            ExchangeSinkHandler sinkHandler = exchange1.createSinkHandler(exchangeId, randomIntBetween(1, 128));