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https://issues.apache.org/jira/browse/LUCENE-8836?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17000923#comment-17000923
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Joel Bernstein commented on LUCENE-8836:
----------------------------------------
This ticket SOLR-13892 implements this as one of many optimizations of a cross
core join. Here is the impl from the patch:
{code:java}
+ private long lookupTerm(SortedSetDocValues docValues, BytesRef key, long
startOrd) throws IOException {
+ long low = startOrd;
+ long high = docValues.getValueCount()-1;
+
+ while (low <= high) {
+ long mid = (low + high) >>> 1;
+ final BytesRef term = docValues.lookupOrd(mid);
+ int cmp = term.compareTo(key);
+
+ if (cmp < 0) {
+ low = mid + 1;
+ } else if (cmp > 0) {
+ high = mid - 1;
+ } else {
+ return mid; // key found
+ }
+ }
+
+ return -(low + 1); // key not found.
+ }
+ {code}
Having this in Lucene would be great.
> Optimize DocValues TermsDict to continue scanning from the last position when
> possible
> --------------------------------------------------------------------------------------
>
> Key: LUCENE-8836
> URL: https://issues.apache.org/jira/browse/LUCENE-8836
> Project: Lucene - Core
> Issue Type: Improvement
> Reporter: Bruno Roustant
> Priority: Major
> Labels: docValues, optimization
> Time Spent: 1h 10m
> Remaining Estimate: 0h
>
> Lucene80DocValuesProducer.TermsDict is used to lookup for either a term or a
> term ordinal.
> Currently it does not have the optimization the FSTEnum has: to be able to
> continue a sequential scan from where the last lookup was in the IndexInput.
> For sparse lookups (when searching only a few terms or ordinal) it is not an
> issue. But for multiple lookups in a row this optimization could save
> re-scanning all the terms from the block start (since they are delat encoded).
> This patch proposes the optimization.
> To estimate the gain, we ran 3 Lucene tests while counting the seeks and the
> term reads in the IndexInput, with and without the optimization:
> TestLucene70DocValuesFormat - the optimization saves 24% seeks and 15% term
> reads.
> TestDocValuesQueries - the optimization adds 0.7% seeks and 0.003% term reads.
> TestDocValuesRewriteMethod.testRegexps - the optimization saves 71% seeks and
> 82% term reads.
> In some cases, when scanning many terms in lexicographical order, the
> optimization saves a lot. In some case, when only looking for some sparse
> terms, the optimization does not bring improvement, but does not penalize
> neither. It seems to be worth to always have it.
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