BlobReferenceIterator in DocumentMK makes use of DocumentStore API to query the NodeDocument. This would cause all those NodeDocuments to be added to cache in DocumentStore. Due to this when blob gc is running cache usage would not be that effective due to all the associated churn.
As these NodeDocument are only required for BlobGC logic and its not expected that this document would read again soon it would be better to skip caching of these documents within DocumentStore
Similar requirement exist in VersionGC logic but there we use direct store based API which does not add such documents to the cache