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/EsqlPlugin.java
import org.elasticsearch.common.settings.Setting;
import org.elasticsearch.common.settings.Settings;
import org.elasticsearch.common.settings.SettingsFilter;
import org.elasticsearch.common.util.concurrent.EsExecutors;
import org.elasticsearch.compute.data.Block;
import org.elasticsearch.compute.lucene.LuceneSourceOperator;
import org.elasticsearch.compute.lucene.ValuesSourceReaderOperator;
import org.elasticsearch.compute.operator.AbstractPageMappingOperator;
import org.elasticsearch.compute.operator.DriverStatus;
import org.elasticsearch.compute.operator.LimitOperator;
import org.elasticsearch.compute.operator.MvExpandOperator;
import org.elasticsearch.compute.operator.exchange.ExchangeService;
import org.elasticsearch.compute.operator.exchange.ExchangeSinkOperator;
import org.elasticsearch.compute.operator.exchange.ExchangeSourceOperator;
import org.elasticsearch.env.Environment;
import org.elasticsearch.env.NodeEnvironment;
import org.elasticsearch.indices.IndicesService;
import org.elasticsearch.plugins.ActionPlugin;
import org.elasticsearch.plugins.Plugin;
import org.elasticsearch.repositories.RepositoriesService;
import org.elasticsearch.rest.RestController;
import org.elasticsearch.rest.RestHandler;
import org.elasticsearch.script.ScriptService;
import org.elasticsearch.threadpool.ExecutorBuilder;
import org.elasticsearch.threadpool.FixedExecutorBuilder;
import org.elasticsearch.threadpool.ThreadPool;
import org.elasticsearch.tracing.Tracer;
import org.elasticsearch.watcher.ResourceWatcherService;
import org.elasticsearch.xcontent.NamedXContentRegistry;
import org.elasticsearch.xpack.core.action.XPackInfoFeatureAction;