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From "Adrien Grand (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (LUCENE-5780) OrdinalMap's mapping from global ords to segment ords is sometimes wasteful
Date Fri, 20 Jun 2014 10:04:24 GMT

     [ https://issues.apache.org/jira/browse/LUCENE-5780?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Adrien Grand updated LUCENE-5780:
---------------------------------

    Fix Version/s:     (was: 4.9)
                   4.10

> OrdinalMap's mapping from global ords to segment ords is sometimes wasteful
> ---------------------------------------------------------------------------
>
>                 Key: LUCENE-5780
>                 URL: https://issues.apache.org/jira/browse/LUCENE-5780
>             Project: Lucene - Core
>          Issue Type: Bug
>            Reporter: Adrien Grand
>            Assignee: Adrien Grand
>             Fix For: 5.0, 4.10
>
>
> Robert found a case when the ordinal map can be quite wasteful in terms of memory usage:
in order to be able to resolve values given a global ordinals, it stores two things:
>  - an identifier of the segment where the value is
>  - the difference between the ordinal on the segment and the global ordinal
> The issue is that OrdinalMap currently picks any of the segments that contain the value
but we can do better: we can pick the first segment that has the value. This will help for
two reasons:
>  - it will potentially require fewer bits per value to store the segment ids if NRT segments
don't introduce new values
>  - if all values happen to appear in the first segment, then the map from global ords
to deltas only stores zeros.
> I just tested on an index where all values are in the first segment and this helped reduce
memory usage of the ordinal map by 4x (from 3.5MB to 800KB).



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