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https://issues.apache.org/jira/browse/LUCENE-10318?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17581016#comment-17581016
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Julie Tibshirani edited comment on LUCENE-10318 at 8/17/22 8:51 PM:
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[~jmazanec15] it's great you're interested in looking into this! I don't have 
any prototype or experiments, you're welcome to pick it up.

Removing nodes and repairing the graph could be a nice direction. But for now 
we can keep things simple and assume there's a segment without deletes. If 
that's looking good and shows a nice improvement in index/ merge benchmarks, 
then we can handle deletes in a follow-up.

Edit: Oops, I didn't refresh the page so I missed Mayya's comment. It looks 
like we're in agreement!


was (Author: julietibs):
[~jmazanec15] it's great you're interested in looking into this! I don't have 
any prototype or experiments, you're welcome to pick it up.

Removing nodes and repairing the graph could be a nice direction. But for now 
we can keep things simple and assume there's a segment without deletes. If 
that's looking good and shows a nice improvement in index/ merge benchmarks, 
then we can handle deletes in a follow-up.

> Reuse HNSW graphs when merging segments?
> ----------------------------------------
>
>                 Key: LUCENE-10318
>                 URL: https://issues.apache.org/jira/browse/LUCENE-10318
>             Project: Lucene - Core
>          Issue Type: Improvement
>            Reporter: Julie Tibshirani
>            Priority: Major
>
> Currently when merging segments, the HNSW vectors format rebuilds the entire 
> graph from scratch. In general, building these graphs is very expensive, and 
> it'd be nice to optimize it in any way we can. I was wondering if during 
> merge, we could choose the largest segment with no deletes, and load its HNSW 
> graph into heap. Then we'd add vectors from the other segments to this graph, 
> through the normal build process. This could cut down on the number of 
> operations we need to perform when building the graph.
> This is just an early idea, I haven't run experiments to see if it would 
> help. I'd guess that whether it helps would also depend on details of the 
> MergePolicy.



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