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From "Ankit Jain (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENE-8635) Lazy loading Lucene FST offheap using mmap
Date Wed, 16 Jan 2019 03:05:00 GMT

    [ https://issues.apache.org/jira/browse/LUCENE-8635?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16743577#comment-16743577
] 

Ankit Jain commented on LUCENE-8635:
------------------------------------

 Rally tests use underlying elasticsearch cluster which use cases other than search like
log analytics. I ran 1 iteration for multiple data sets and did not notice significant performance
degradations. Rather, I noticed 6% improvement in indexing throughput for all the data sets.
Though, I should leave it running for more iterations, to get more conclusive evidence.

Thanks [~sokolov] for testing the changes. I think the impact is as expected, maybe slightly
more for the PKLookup. Do the tests use randomized key for each PKLookup query or the keys
are reused across queries? That will impact the overall throughput as mmap is inherently lazily
loaded.

Though, I'm open to exposing per field setting in Lucene, I agree with [~dsmiley] about 25%
reduction in throughput being tiny fraction of typical usage. And, throughput should be better
if same keys get used for PKLookup queries. Adding per field setting might require code change
and will be effective only for data indexed using new codec. My knowledge of Lucene settings
is limited and I might be wrong.

> 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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