# Elastic's plain to support Lucene Load FST offHeap features

**URL:** <https://discuss.elastic.co/t/elastics-plain-to-support-lucene-load-fst-offheap-features/231679>\
**Category:** Elasticsearch\
**Created:** [May 8, 2020, 8:37am UTC](https://discuss.elastic.co/t/elastics-plain-to-support-lucene-load-fst-offheap-features/231679 "2020-05-08T08:37:30Z")\
**Posts on this page:** 9\
**Page:** 1

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**Author:** ![hackerwin7](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/hackerwin7/32/43223_2.png) [@hackerwin7](https://discuss.elastic.co/u/hackerwin7)\
**Post date:** [May 8, 2020, 8:37am UTC](https://discuss.elastic.co/t/elastics-plain-to-support-lucene-load-fst-offheap-features/231679/1 "2020-05-08T08:37:30Z")

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Related to this: [https://issues.apache.org/jira/browse/LUCENE-8635](https://issues.apache.org/jira/browse/LUCENE-8635)

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**Author:** ![DavidTurner](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/davidturner/32/22453_2.png) [@DavidTurner](https://discuss.elastic.co/u/DavidTurner)\
**Post date:** [May 8, 2020, 9:08am UTC](https://discuss.elastic.co/t/elastics-plain-to-support-lucene-load-fst-offheap-features/231679/2 "2020-05-08T09:08:39Z")

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What's the question?

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**Author:** ![hackerwin7](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/hackerwin7/32/43223_2.png) [@hackerwin7](https://discuss.elastic.co/u/hackerwin7)\
**Post date:** [May 8, 2020, 9:19am UTC](https://discuss.elastic.co/t/elastics-plain-to-support-lucene-load-fst-offheap-features/231679/3 "2020-05-08T09:19:20Z")

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[https://issues.apache.org/jira/browse/LUCENE-8671](https://issues.apache.org/jira/browse/LUCENE-8671)

According to this, Lucene have attribute to put On/OffHeapStore when creating its FST.  
dose ES plain to import this to set the attribute to put which FST to heap or offHeap store.

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<div class="post-metadata">

**Author:** ![hackerwin7](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/hackerwin7/32/43223_2.png) [@hackerwin7](https://discuss.elastic.co/u/hackerwin7)\
**Post date:** [May 8, 2020, 9:24am UTC](https://discuss.elastic.co/t/elastics-plain-to-support-lucene-load-fst-offheap-features/231679/4 "2020-05-08T09:24:06Z")

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background: [https://www.elastic.co/blog/significantly-decrease-your-elasticsearch-heap-memory-usage](https://www.elastic.co/blog/significantly-decrease-your-elasticsearch-heap-memory-usage)

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<div class="post-metadata">

**Author:** ![DavidTurner](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/davidturner/32/22453_2.png) [@DavidTurner](https://discuss.elastic.co/u/DavidTurner)\
**Post date:** [May 8, 2020, 9:30am UTC](https://discuss.elastic.co/t/elastics-plain-to-support-lucene-load-fst-offheap-features/231679/5 "2020-05-08T09:30:37Z")

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Ok, yes, Elasticsearch already uses off-heap FSTs quite a lot and 7.7.0 will do so even more as detailed in the blog post you linked.

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<div class="post-metadata">

**Author:** ![hackerwin7](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/hackerwin7/32/43223_2.png) [@hackerwin7](https://discuss.elastic.co/u/hackerwin7)\
**Post date:** [May 8, 2020, 9:34am UTC](https://discuss.elastic.co/t/elastics-plain-to-support-lucene-load-fst-offheap-features/231679/6 "2020-05-08T09:34:46Z")

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> <https://github.com/elastic/elasticsearch/issues/38390>
>
> Lucene is adding support for loading terms index offheap using mapped files. Elasticsearch should expose settings to specify list of fields...

It seems like ES do not intend to expose this level settings to load lazily FST offHeap ?

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<div class="post-metadata">

**Author:** ![DavidTurner](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/davidturner/32/22453_2.png) [@DavidTurner](https://discuss.elastic.co/u/DavidTurner)\
**Post date:** [May 8, 2020, 9:38am UTC](https://discuss.elastic.co/t/elastics-plain-to-support-lucene-load-fst-offheap-features/231679/7 "2020-05-08T09:38:30Z")

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Correct, it's not something you can directly control with a setting. It's done automatically.

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<div class="post-metadata">

**Author:** ![hackerwin7](https://sea2.discourse-cdn.com/elastic/user_avatar/discuss.elastic.co/hackerwin7/32/43223_2.png) [@hackerwin7](https://discuss.elastic.co/u/hackerwin7)\
**Post date:** [May 8, 2020, 9:44am UTC](https://discuss.elastic.co/t/elastics-plain-to-support-lucene-load-fst-offheap-features/231679/8 "2020-05-08T09:44:33Z")

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Thanks

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**Author:** ![system](https://us1.discourse-cdn.com/elastic/original/3X/1/a/1ac57faf039f6b580b3f104ef42a2a89e41014de.png) [@system](https://discuss.elastic.co/u/system)\
**Post date:** [June 5, 2020, 9:44am UTC](https://discuss.elastic.co/t/elastics-plain-to-support-lucene-load-fst-offheap-features/231679/9 "2020-06-05T09:44:52Z")

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