Online insertion, removal of points

[zgornel]

Mostly refering to https://github.com/andrusha97/online-hnsw
Have no ideea of the costs involved but it may prove useful. The mechanism is probably mostly in place through insert_point! but it would be cool to have

# we assume to some `hnsw` object already defined with an index
# hnsw = HierarchicalNSW(...)
# add_to_graph!(hnsw)
push!(hnsw, point)  # point::AbstractVector
remove!(hnsw, index)  # index::Int

[JonasIsensee]

This should be possible.
I opted out of doing this initially because for a fixed-size graph I can preallocate all the relevant arrays.
Also, at the moment the implementation does not modify nor copy the input dataset.
Instead it indexes into the data.

To push! a point into the graph one would need to push it into the data set.

Deleting is a bit more difficult. What do you do with the nodes that pointed towards the deleted nodes. (And how do you find them? I'm don't remember if we have only bidirectional links)

[zgornel]

I do not know; deletion may be indeed complex and the structure (probably all nsw's) not designed for fast updates.