Elastic Search synonyms - Delete Action

Question

Are synonyms in Elastic Search (version 6.2.3) stored in the items when these are created/updated or are synonyms applied in every search query to the index?

We need to remove the synonyms of an index with 6 million items and I cannot see in the documentation if removing these synonyms from the index will be enough

DELETE /api/as/v1/engines/{ENGINE_NAME}/synonyms/{SYNONYM_SET_ID}

Or it is needed to reindex all the items afterwards, in which case it might be better to delete the current index and create a new one.

Answer 1

1. If synonyms are applied during inserting the document

   • Deletion of current synonyms, won't change anything in the existing data of an index, existing data should be searchable by synonyms.

2. If synonyms are applied during query time

   • In this case, removing the synonyms will stop searching the document using synonym.

Now the question is whether you are using index-time-analysis or query-time-analysis. You can check in your mappings. E.g

"mappings": {
    "properties": {
      "text": {
        "type": "text",
        "analyzer": "autocomplete", // <======== For index time analysis
        "search_analyzer": "synonym_analyzer" //<====== For Query time analysis  
      }
    }
  }
}