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https://issues.apache.org/jira/browse/LUCENE-8635?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16743137#comment-16743137
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Michael McCandless commented on LUCENE-8635:
--------------------------------------------
Thanks for testing [~sokolov] – the results make sense: the most terms
dictionary intensive queries are impacted the most, with {{PKLookup}} being
heavily impacted since that's just purely exercising the terms dictionary with
no postings visited. Fuzzy queries, and then queries matching few hits
(conjunctions with low/medium freq terms) also spend relatively more time in
the terms dictionary ...
So net/net it looks like we should not make this the default, but expose it
somehow as an option for those use cases that don't want to dedicate heap
memory to storing FSTs?
> Lazy loading Lucene FST offheap using mmap
> ------------------------------------------
>
> Key: LUCENE-8635
> URL: https://issues.apache.org/jira/browse/LUCENE-8635
> Project: Lucene - Core
> Issue Type: New Feature
> Components: core/FSTs
> Environment: I used below setup for es_rally tests:
> single node i3.xlarge running ES 6.5
> es_rally was running on another i3.xlarge instance
> Reporter: Ankit Jain
> Priority: Major
> Attachments: offheap.patch, rally_benchmark.xlsx
>
>
> Currently, FST loads all the terms into heap memory during index open. This
> causes frequent JVM OOM issues if the term size gets big. A better way of
> doing this will be to lazily load FST using mmap. That ensures only the
> required terms get loaded into memory.
>
> Lucene can expose API for providing list of fields to load terms offheap. I'm
> planning to take following approach for this:
> # Add a boolean property fstOffHeap in FieldInfo
> # Pass list of offheap fields to lucene during index open (ALL can be
> special keyword for loading ALL fields offheap)
> # Initialize the fstOffHeap property during lucene index open
> # FieldReader invokes default FST constructor or OffHeap constructor based
> on fstOffHeap field
>
> I created a patch (that loads all fields offheap), did some benchmarks using
> es_rally and results look good.
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