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
sourceHandler.addRemoteSink(exchange0.newRemoteSink(task, exchangeId, node0, node1.getLocalNode()), randomIntBetween(1, 5));
            Exception err = expectThrows(
                Exception.class,
                () -> runConcurrentTest(maxSeqNo, maxSeqNo, sourceHandler::createExchangeSource, sinkHandler::createExchangeSink)
            );
            Throwable cause = ExceptionsHelper.unwrap(err, IOException.class);
            assertNotNull(cause);
            assertThat(cause.getMessage(), equalTo("page is too large"));
        }
    }
    private MockTransportService newTransportService() {
        List<NamedWriteableRegistry.Entry> namedWriteables = new ArrayList<>(ClusterModule.getNamedWriteables());
        namedWriteables.addAll(Block.getNamedWriteables());
        NamedWriteableRegistry namedWriteableRegistry = new NamedWriteableRegistry(namedWriteables);
        MockTransportService service = MockTransportService.createNewService(
            Settings.EMPTY,
            MockTransportService.newMockTransport(Settings.EMPTY, TransportVersion.current(), threadPool, namedWriteableRegistry),
            VersionInformation.CURRENT,
            threadPool,
            null,
            Collections.emptySet()
        );
        service.start();
        service.acceptIncomingRequests();
        return service;
    }
    private int randomExchangeBuffer() {
        return randomBoolean() ? randomIntBetween(1, 3) : randomIntBetween(1, 128);
    }
    private static class FilterTransportChannel implements TransportChannel {