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
sinkHandler = randomFrom(sinkHandlers);
            } else {
                sinkHandler = new ExchangeSinkHandler(randomExchangeBuffer(), threadPool::relativeTimeInMillis);
                sourceExchanger.addRemoteSink(sinkHandler::fetchPageAsync, randomIntBetween(1, 3));
                sinkHandlers.add(sinkHandler);
            }
            return sinkHandler.createExchangeSink();
        };
        final int maxInputSeqNo = rarely() ? -1 : randomIntBetween(0, 50_000);
        final int maxOutputSeqNo = rarely() ? -1 : randomIntBetween(0, 50_000);
        runConcurrentTest(maxInputSeqNo, maxOutputSeqNo, sourceExchanger::createExchangeSource, exchangeSink);
    }
    public void testEarlyTerminate() {
        IntBlock block = new ConstantIntVector(1, 2).asBlock();
        Page p1 = new Page(block);
        Page p2 = new Page(block);
        ExchangeSinkHandler sinkExchanger = new ExchangeSinkHandler(2, threadPool::relativeTimeInMillis);
        ExchangeSink sink = sinkExchanger.createExchangeSink();
        sink.addPage(p1);
        sink.addPage(p2);
        assertFalse(sink.waitForWriting().isDone());
        PlainActionFuture<ExchangeResponse> future = new PlainActionFuture<>();
        sinkExchanger.fetchPageAsync(true, future);
        ExchangeResponse resp = future.actionGet();
        assertTrue(resp.finished());
        assertNull(resp.page());
        assertTrue(sink.waitForWriting().isDone());
        assertTrue(sink.isFinished());
    }
    public void testConcurrentWithTransportActions() throws Exception {