why ivf index so big?

[huaimin016]

I use select * from pg_vector_index_stat; to checkout index size, here is the result:

19176892	19177456	pgvecto_rs_90_ivf	pgvecto_rs_90_ivf_vector_idx	NORMAL	false	2781540	{2781540}	{}	0	1580896555	{"vector":{"dimensions":512,"vector":"Veci8","distance":"Cos"},"segment":{"max_growing_segment_size":20000,"max_sealed_segment_size":30000000},"indexing":{"ivf":{"least_iterations":16,"iterations":500,"nlist":1000,"nsample":65536,"quantization":{"trivial":{}}}}}

In disk:

postgres@dddddd:~/16/main/pg_vectors/indexes/0000000000000000000000000000000066d137b44b7ae9220000000501249ff0$ du . -h
21M	./segments/51f8e269-845f-4154-8558-629302f1fa7f/indexing/quantization
1.5G	./segments/51f8e269-845f-4154-8558-629302f1fa7f/indexing/raw
1.5G	./segments/51f8e269-845f-4154-8558-629302f1fa7f/indexing
1.5G	./segments/51f8e269-845f-4154-8558-629302f1fa7f
1.5G	./segments
8.0K	./startup
1.5G	.

why need raw index data? This increases the memory usage a lot. Is it necessary to save raw index data? Will this data be loaded into memory?