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https://issues.apache.org/jira/browse/LUCENE-5609?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13974356#comment-13974356
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Robert Muir commented on LUCENE-5609:
-------------------------------------
To be simple, i think a change we make has to be a multiple of 4: the current
default.
This way we have easy backwards compat with existing indexes for users that
just go with the default (since NumericRangeQuery has ctors that use the
default precisionStep, and multiples of the index-time work at query-time).
Otherwise, it could cause a lot of confusion.
> Should we revisit the default numeric precision step?
> -----------------------------------------------------
>
> Key: LUCENE-5609
> URL: https://issues.apache.org/jira/browse/LUCENE-5609
> Project: Lucene - Core
> Issue Type: Improvement
> Components: core/search
> Reporter: Michael McCandless
> Fix For: 4.9, 5.0
>
>
> Right now it's 4, for both 8 (long/double) and 4 byte (int/float)
> numeric fields, but this is a pretty big hit on indexing speed and
> disk usage, especially for tiny documents, because it creates many (8
> or 16) terms for each value.
> Since we originally set these defaults, a lot has changed... e.g. we
> now rewrite MTQs per-segment, we have a faster (BlockTree) terms dict,
> a faster postings format, etc.
> Index size is important because it limits how much of the index will
> be hot (fit in the OS's IO cache). And more apps are using Lucene for
> tiny docs where the overhead of individual fields is sizable.
> I used the Geonames corpus to run a simple benchmark (all sources are
> committed to luceneutil). It has 8.6 M tiny docs, each with 23 fields,
> with these numeric fields:
> * lat/lng (double)
> * modified time, elevation, population (long)
> * dem (int)
> I tested 4, 8 and 16 precision steps:
> {noformat}
> indexing:
> PrecStep Size IndexTime
> 4 1812.7 MB 651.4 sec
> 8 1203.0 MB 443.2 sec
> 16 894.3 MB 361.6 sec
> searching:
> Field PrecStep QueryTime TermCount
> geoNameID 4 2872.5 ms 20306
> geoNameID 8 2903.3 ms 104856
> geoNameID 16 3371.9 ms 5871427
> latitude 4 2160.1 ms 36805
> latitude 8 2249.0 ms 240655
> latitude 16 2725.9 ms 4649273
> modified 4 2038.3 ms 13311
> modified 8 2029.6 ms 58344
> modified 16 2060.5 ms 77763
> longitude 4 3468.5 ms 33818
> longitude 8 3629.9 ms 214863
> longitude 16 4060.9 ms 4532032
> {noformat}
> Index time is with 1 thread (for identical index structure).
> The query time is time to run 100 random ranges for that field,
> averaged over 20 iterations. TermCount is the total number of terms
> the MTQ rewrote to across all 100 queries / segments, and it gets
> higher as expected as precStep gets higher, but the search time is not
> that heavily impacted ... negligible going from 4 to 8, and then some
> impact from 8 to 16.
> Maybe we should increase the int/float default precision step to 8 and
> long/double to 16? Or both to 16?
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