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
ExchangeSinkOperator sinkOperator = new ExchangeSinkOperator(exchangeSink.get(), Function.identity());
            DriverContext dc = new DriverContext();
            Driver d = new Driver("test-session:1", dc, () -> description, seqNoGenerator.get(dc), List.of(), sinkOperator, () -> {});
            drivers.add(d);
        }
        for (int i = 0; i < numSources; i++) {
            String description = "source-" + i;
            ExchangeSourceOperator sourceOperator = new ExchangeSourceOperator(exchangeSource.get());
            DriverContext dc = new DriverContext();
            Driver d = new Driver("test-session:2", dc, () -> description, sourceOperator, List.of(), seqNoCollector.get(dc), () -> {});
            drivers.add(d);
        }
        PlainActionFuture<Void> future = new PlainActionFuture<>();
        new DriverRunner() {
            @Override
            protected void start(Driver driver, ActionListener<Void> listener) {
                Driver.start(threadPool.executor(ESQL_TEST_EXECUTOR), driver, between(1, 10000), listener);
            }
        }.runToCompletion(drivers, future);
        future.actionGet(TimeValue.timeValueMinutes(1));
        var expectedSeqNos = IntStream.range(0, Math.min(maxInputSeqNo, maxOutputSeqNo)).boxed().collect(Collectors.toSet());
        assertThat(seqNoCollector.receivedSeqNos, hasSize(expectedSeqNos.size()));
        assertThat(seqNoCollector.receivedSeqNos, equalTo(expectedSeqNos));
    }
    public void testConcurrentWithHandlers() {
        var sourceExchanger = new ExchangeSourceHandler(randomExchangeBuffer(), threadPool.executor(ESQL_TEST_EXECUTOR));
        List<ExchangeSinkHandler> sinkHandlers = new ArrayList<>();
        Supplier<ExchangeSink> exchangeSink = () -> {
            final ExchangeSinkHandler sinkHandler;
            if (sinkHandlers.isEmpty() == false && randomBoolean()) {