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https://issues.apache.org/jira/browse/LUCENE-8635?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16755389#comment-16755389
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Ankit Jain edited comment on LUCENE-8635 at 1/29/19 9:20 PM:
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{quote}Given that the performance hit is mostly on PK lookups, maybe a starting
point could be to always put the FST off-heap except when docCount ==
sumDocFreq, which suggests the field is an ID field.{quote}
[~jpountz] - Does that exlude autogenerated id fields that are uuid, resulting
in large FSTs? Elasticsearch for example has _id field, which IMO is better
offheap.
was (Author: akjain):
{quote}Given that the performance hit is mostly on PK lookups, maybe a starting
point could be to always put the FST off-heap except when docCount ==
sumDocFreq, which suggests the field is an ID field.{quote}
[~jpountz] - Does that exlude autogenerated id fields that are uuid, resulting
in huge FST? Elasticsearch for example has _id field, that is better offheap.
> 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: fst-offheap-ra-rev.patch, fst-offheap-rev.patch,
> offheap.patch, optional_offheap_ra.patch, ra.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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