increase execute thread pool size (opensearch-project#2691) (opensearch-project#2699)

Signed-off-by: Yaliang Wu <ylwu@amazon.com>
(cherry picked from commit b980199)

Co-authored-by: Yaliang Wu <ylwu@amazon.com>

Author: opensearch-trigger-bot[bot]

plugin/src/main/java/org/opensearch/ml/plugin/MachineLearningPlugin.java

@@ -835,8 +835,8 @@ public List<ExecutorBuilder<?>> getExecutorBuilders(Settings settings) {
         FixedExecutorBuilder executeThreadPool = new FixedExecutorBuilder(
             settings,
             EXECUTE_THREAD_POOL,
-            Math.max(1, OpenSearchExecutors.allocatedProcessors(settings) - 1),
-            10,
+            OpenSearchExecutors.allocatedProcessors(settings) * 4,
+            10000,
             ML_THREAD_POOL_PREFIX + EXECUTE_THREAD_POOL,
             false
         );