Disable concurrent segment search for system indices and throttled search requests

Signed-off-by: Jay Deng <jayd0104@gmail.com>

Author: jed326

CHANGELOG.md

@@ -107,6 +107,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Add a counter to node stat api to track shard going from idle to non-idle ([#12768](https://github.com/opensearch-project/OpenSearch/pull/12768))
 - Allow setting KEYSTORE_PASSWORD through env variable ([#12865](https://github.com/opensearch-project/OpenSearch/pull/12865))
 - [Concurrent Segment Search] Perform buildAggregation concurrently and support Composite Aggregations ([#12697](https://github.com/opensearch-project/OpenSearch/pull/12697))
+- [Concurrent Segment Search] Disable concurrent segment search for system indices and throttled requests ([#12697](https://github.com/opensearch-project/OpenSearch/pull/12697))
 
 ### Dependencies
 - Bump `org.apache.commons:commons-configuration2` from 2.10.0 to 2.10.1 ([#12896](https://github.com/opensearch-project/OpenSearch/pull/12896))

server/src/main/java/org/opensearch/search/DefaultSearchContext.java

@@ -902,7 +902,11 @@ public boolean shouldUseConcurrentSearch() {
      * Evaluate if parsed request supports concurrent segment search
      */
     public void evaluateRequestShouldUseConcurrentSearch() {
-        if (sort != null && sort.isSortOnTimeSeriesField()) {
+        // Do not use concurrent segment search for system indices or throttled requests. See:
+        // https://github.com/opensearch-project/OpenSearch/issues/12951
+        if (indexShard.isSystem() || indexShard.indexSettings().isSearchThrottled()) {
+            requestShouldUseConcurrentSearch.set(false);
+        } else if (sort != null && sort.isSortOnTimeSeriesField()) {
             requestShouldUseConcurrentSearch.set(false);
         } else if (aggregations() != null
             && aggregations().factories() != null