I’m not an index expert, but since the index usage doesn’t depend on the number of documents, why not do your iterative testing with a small number of documents? That’s the best advice I have for reducing the index building time.
I’m a bit confused with :
“Now when I try to create a new index, the remaining mutations is climbing to 670m. I remember initially it was around 85m, a little over number of documents in the collection.”
It was 300m according to your first post. Almost 4x the number of documents.
“One collection has 84.5m items. However when I tried to create a new index, it showed 300m+ mutations were remaining.”
“Now when I try to create a new index, the remaining mutations is climbing to 670m”
It appears that the number of mutations depends on the index definition. I wonder if that 670m includes deleting the original index?