Migrating large ArrayInvertedLists into OnDiskInvertedLists with write permission

[pablocael]

Hi there, I have several really large indices, and I would like to start managing them using odil, but I dont want recreate the index. I want to ask if there is a way of migrating and existing index creating in a regular way to OnDiskInvertedLists with write permissions and unpacked data (e.g: separate ivf files on disk).
I could imagine I can go through the lists and add to the odil similar to what merge_ondisk does (here).
Is there an api for that? Will just migrating the lists to the odil class work?

Thanks in advance

[pablocael]

One solution worked for me to make indices writable on disk is:

1. load in RAM memory using large RAM specs
2. remove all elements from index and save the trained empty index
3. use merge_ondisk to merge both full and empty trained index and move the IVF to an external unpacked file.

from there onwards the index can be loaded and updated in disk as OnDiskInvertedLists will have read-only flag to false.