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
final AtomicInteger nextSeqNo = new AtomicInteger(-1);
        final int maxInputSeqNo;
        SeqNoGenerator(int maxInputSeqNo) {
            this.maxInputSeqNo = maxInputSeqNo;
        }
        @Override
        public String describe() {
            return "SeqNoGenerator(maxInputSeqNo=" + maxInputSeqNo + ")";
        }
        @Override
        public SourceOperator get(DriverContext driverContext) {
            return new SourceOperator() {
                @Override
                public void finish() {