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/src/main/java/org/elasticsearch/xpack/esql/plugin/ComputeService.java
}),
            threadContext
        );
        try (ThreadContext.StoredContext ignored = threadContext.newStoredContextPreservingResponseHeaders()) {
            threadContext.markAsSystemContext();
            SearchShardsRequest searchShardsRequest = new SearchShardsRequest(
                originalIndices,
                SearchRequest.DEFAULT_INDICES_OPTIONS,
                filter,
                null,
                null,
                false,
                null
            );
            transportService.sendChildRequest(
                transportService.getLocalNode(),
                SearchShardsAction.NAME,
                searchShardsRequest,
                parentTask,
                TransportRequestOptions.EMPTY,
                new ActionListenerResponseHandler<>(
                    preservingContextListener,
                    SearchShardsResponse::new,
                    TransportResponseHandler.TRANSPORT_WORKER
                )
            );
        }
    }
    
    private static class DataNodeResponse extends TransportResponse {