[GitHub] [calcite] danny0405 commented on a change in pull request #1529: [CALCITE-3442] In ElasticSearch adapter, set `stored_fields = _none_` to prohibit FetchPhase get involved

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danny0405 commented on a change in pull request #1529: [CALCITE-3442] In ElasticSearch adapter, set `stored_fields = _none_` to prohibit FetchPhase get involved 
URL: https://github.com/apache/calcite/pull/1529#discussion_r339441621
 
 

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 File path: elasticsearch/src/main/java/org/apache/calcite/adapter/elasticsearch/ElasticsearchTable.java
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 @@ -186,6 +186,11 @@ String scriptedFieldPrefix() {
     query.put("_source", false);
     query.put("size", 0);
     query.remove("script_fields");
+    // set _source = false and size = 0, `FetchPhase` would still be executed
+    // to fetch the metadata fields and visit the Lucene stored_fields,
+    // which would lead to performance declined dramatically.
+    // `stored_fields = _none` can prohibit such behavior entirely
+    query.put("stored_fields", "_none_");
 
 Review comment:
   Sounds reasonable, do you think we can add a test case for this ? Some code to  illustrates that the `FetchPhase` you mentioned has indeed been triggered without your fix.

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