During ingestion createField in FieldType is being called for each field on each document. For the subclasses of FieldType without their own implementation of createField the lucene version of FieldType is created to be stored along with the value. However the lucene FieldType object is identical when created from the same SchemaField. In testing ingestion of one million rows with 22 field each we were creating 22 million lucene FieldType objects when only 22 are needed. Solr should lazily initialize a lucene FieldType for each SchemaField and reuse them for future ingestion. Not only does this relieve memory usage but also relieves significant pressure on the gc.
There are also subclasses of Solr FieldType which create separate Lucene FieldType for stored fields instead of reusing the static in StoredField.