Reduce concurrent clients (elastic#128841) (elastic#128879)

Author: idegtiarenko

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/plugin/QueryPragmas.java

@@ -31,7 +31,7 @@
  */
 public final class QueryPragmas implements Writeable {
     public static final Setting<Integer> EXCHANGE_BUFFER_SIZE = Setting.intSetting("exchange_buffer_size", 10);
-    public static final Setting<Integer> EXCHANGE_CONCURRENT_CLIENTS = Setting.intSetting("exchange_concurrent_clients", 3);
+    public static final Setting<Integer> EXCHANGE_CONCURRENT_CLIENTS = Setting.intSetting("exchange_concurrent_clients", 2);
     public static final Setting<Integer> ENRICH_MAX_WORKERS = Setting.intSetting("enrich_max_workers", 1);
 
     private static final Setting<Integer> TASK_CONCURRENCY = Setting.intSetting(