set_ef causes Segmentation Fault

[louisabraham]

The following code segfaults:

import hnswlib

n_docs, dim = 7571305, 100

index = hnswlib.Index("l2", dim)
index.set_num_threads(16)
index.set_ef(10)

Python 3.7.1
hnswlib==0.3

I installed it yesterday from github with python3 setup.py install.

[louisabraham]

I think the index must be initialized before.

It is not clear what parameters are dumped with the index and what parameters must be reset.

As a side note, https://docs.python.org/3/library/faulthandler.html is super useful to diagnose segfaults!

[yurymalkov]

Hi @louisabraham
Yes, the index has to be initialized first. There is no check for that - it should be fixed.

ef_ is not currently dumped with the index. I'll update the docs to reflect this.
It is a good idea to store the ef_ in the dumped index, but this needs an overhaul of the format to make it extendable and avoid such problems in the future.