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 boolean isFinished() {
                    return nextSeqNo.get() >= maxInputSeqNo;
                }
                @Override
                public Page getOutput() {
                    if (randomInt(100) < 5) {
                        return null;
                    }
                    int size = randomIntBetween(1, 10);
                    IntBlock.Builder builder = IntBlock.newBlockBuilder(size);
                    for (int i = 0; i < size; i++) {
                        int seqNo = nextSeqNo.incrementAndGet();
                        if (seqNo < maxInputSeqNo) {
                            builder.appendInt(seqNo);
                        }
                    }
                    return new Page(builder.build());
                }
                @Override
                public void close() {
                }
            };
        }
    }
    /**
     * Collects the received sequence numbers that are less than {@code maxOutputSeqNo}.
     */
    static final class SeqNoCollector implements SinkOperator.SinkOperatorFactory {