Cluster becomes too slow when indexing knn_vector data

Hi all,

I have a 6 node cluster (2 master and 4 data) and I created an index with nested knn_vector field. I am noticing the whole cluster becoming too slow during indexing. Once indexing is complete, the performance gradually becomes better.

Note that I am indexing around 36000 document with each document may have 100 nested vectors. Each vector is of size 64.

Any recommendation on how to overcome such slowness?