When indexing signals, Fusion uses a default index pipeline named _signals_ingest unless you specify a different index pipeline. The _signals_ingest index pipeline has five stages:
  1. Format Signals stage
  2. Field Mapping stage
  3. GeoIP Lookup stage
  4. Solr Indexer stage
  5. Update has_clicks flag stage
    The Update has_clicks flag stage is an instance of the Update Related Document stage that updates the has_clicks flag to “true” on an existing request signal after the first click signal is processed for the request.     Update Related Documents stage configuration
The update stage works as follows:
  1. When a click signal is encountered (type == click)
  2. Look at the incoming click signal for a field named request_id_s, which gets set by the Format Signals stage using a distributed cache of recently processed request signals. If the request_id_s field is set, then send a real-time GET query to Solr to find a request signal with ID equal to the value of the request_id_s field on the click signal. To avoid re-updating request signals, the RTG query also filters on has_clicks==false, which avoids duplicate atomic updates on the same document in Solr. Real-time GET is used to avoid timing issues between a request signal being sent to Solr and when it gets committed. This prevents missing updates when clicks occur soon after the initial request signal is sent by the search app.
  3. If the click signal does not have the request_id_s field set, then do a normal Solr lookup for the request signal using: +query_id:"${query_id}" +type:request +has_clicks:false. A click signal may not have a request_id_s if there is a cache miss in the distributed cache used by the Format Signals stage.
  4. If the stage performs a normal query, there may be multiple request signals that have the same query_id. This is because the query_id is based on session + query + filter, so if a user sends the same query + filter during the same session, there will be multiple request signals with the same query_id value. Thus, the stage sorts to get the latest request signal to update.
  5. If a related document is found (in this case a request signal), then the stage updates the has_clicks field to true and performs an atomic update in Solr.
This stage performs its work in a background thread, so it does not impact the indexing performance of the click signal.