[CALCITE-3442] In ElasticSearch adapter, set `stored_fields = _none_` to prohibit FetchPhase get involved

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 1.22.0
• Component/s: elasticsearch-adapter
• Labels: performance pull-request-available
• Flags: Patch, Important
• Assignee: Danny Chen
• Reporter: yunfeng
• Created: 24/Oct/19 07:29
• Updated: 06/Mar/20 04:34
• Resolved: 29/Oct/19 02:37

Description

For elasticsearch-adapter, when ElasticsearchAggregate involved , set _source = false and size = 0 , Elasticsearch `FetchPhase` would still be executed against the current search process and visit the Lucene stored_fields, which would lead to performance declined dramatically.
We can set `stored_fields = _none` prohibit this such behavior entirely, and skip the Elasticsearch's `fetch phase` which would bring time-consuming `fetch phase` for metadata fields such as '_id' etc.

Issue Links

• links to: GitHub Pull Request #1529