Logstash filter for parsing nested json

I am trying to ingest a nested json file from couchdb using couchdb_changes plugin ,since the number of fields are very huge I tried with increasing the maximum number of field parameter for the index
but finally Elasticsearch crashed due to out of memory . so now I want to a configure the logstash filter to forward only the minimal required fields to Elasticsearch , i tried ingesting only part of the data to see the the field names in ES ,it appears like below ...

doc.docs.data.<cluster_name>.<domain_name>.numCpuCores , As you can see here numCpuCores only contant in this field , Please suggest a way to parse only the required fields to ES .