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https://issues.apache.org/jira/browse/SOLR-7730?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14660748#comment-14660748
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Yonik Seeley commented on SOLR-7730:
------------------------------------
bq. how much gain did you evidence?
I actually didn't benchmark it because after I looked at the code in context,
it became obvious :-) (and I didn't have a docvalues index lying around...)
Remember to backport your last commit to 5x! In case you're not familiar with
the standard way, to merge back a commit from trunk to 5x, it's
{code}
#execute in the root of an up-to-date 5x checkout:
svn merge -c 1694563 https://svn.apache.org/repos/asf/lucene/dev/trunk
{code}
I actually have a shell variable set up to make it shorter:
T=https://svn.apache.org/repos/asf/lucene/dev/trunk
> speed-up faceting on doc values fields
> --------------------------------------
>
> Key: SOLR-7730
> URL: https://issues.apache.org/jira/browse/SOLR-7730
> Project: Solr
> Issue Type: Improvement
> Components: faceting
> Affects Versions: 5.2.1
> Reporter: Mikhail Khludnev
> Labels: patch
> Fix For: 5.3
>
> Attachments: LUCENE-7730.patch, LUCENE-7730.patch, SOLR-7730.patch
>
>
> every time we count facets on DocValues fields in Solr on many segments index
> we see the unnecessary hotspot:
> {code}
> ....
> at
> org.apache.lucene.index.MultiFields.getMergedFieldInfos(MultiFields.java:248)
> at
> org.apache.lucene.index.SlowCompositeReaderWrapper.getFieldInfos(SlowCompositeReaderWrapper.java:239)
> at
> org.apache.lucene.index.SlowCompositeReaderWrapper.getSortedSetDocValues(SlowCompositeReaderWrapper.java:176)
> at
> org.apache.solr.request.DocValuesFacets.getCounts(DocValuesFacets.java:72)
> at
> org.apache.solr.request.SimpleFacets.getTermCounts(SimpleFacets.java:460) ....
> {code}
> the reason is SlowCompositeReaderWrapper.getSortedSetDocValues() Line 136 and
> SlowCompositeReaderWrapper.getSortedDocValues() Line 174
> before return composite doc values, SCWR merges segment field infos, which is
> expensive, but after fieldinfo is merged, it checks *only* docvalue type in
> it. This dv type check can be done much easier in per segment basis.
> This patch gets some performance gain for those who count DV facets in Solr.
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