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https://issues.apache.org/jira/browse/LUCENE-7255?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15258025#comment-15258025
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Andrés de la Peña commented on LUCENE-7255:
-------------------------------------------
I was thinking in being able to build a {{EarlyTerminatingSortingCollector}}
just with the number of wanted documents, either changing the meaning of the
argument:
{code}
- public EarlyTerminatingSortingCollector(Collector in, Sort sort, int
numDocsToCollect, Sort mergePolicySort) {
- ...
- }
+ public EarlyTerminatingSortingCollector(Collector in, Sort sort, int
numWanted, Sort mergePolicySort) {
+ ...
+ }
{code}
or maybe adding a new method:
{code}
+ public EarlyTerminatingSortingCollector buildWithWanted(Collector in, Sort
sort, int numWanted, Sort mergePolicySort) {
+ ...
+ }
{code}
This way, if it is possible, the paging state managed by users would be
composed only by the last {{FieldDoc}}, as it is done by other collectors.
Otherwise, if I'm right, the paging state managed by users using sorted indexes
should be composed by both the last {{FieldDoc}} and also the number of already
collected documents, and an hypothetical {{IndexSearcher}} aware of index
sorting such as the proposed by
[LUCENE-6766|https://issues.apache.org/jira/browse/LUCENE-6766] should modify
its {{searchAfter}} method to require the number of documents to skip.
> Paging with SortingMergePolicy and EarlyTerminatingSortingCollector
> -------------------------------------------------------------------
>
> Key: LUCENE-7255
> URL: https://issues.apache.org/jira/browse/LUCENE-7255
> Project: Lucene - Core
> Issue Type: Bug
> Affects Versions: 5.3, 5.4, 5.5, 6.0
> Reporter: Andrés de la Peña
> Labels: EarlyTerminatingSortingCollector, pagination, paging,
> searchafter, sortingmergepolicy
>
> {{EarlyTerminatingSortingCollector}} seems to don't work when used with a
> {{TopDocsCollector}} searching for documents after a certain {{FieldDoc}}.
> That is, it can't be used for paging. The following code allows to reproduce
> the problem:
> {code}
> // Sort to be used both with merge policy and queries
> Sort sort = new Sort(new SortedNumericSortField(FIELD_NAME,
> SortField.Type.INT));
> // Create directory
> RAMDirectory directory = new RAMDirectory();
> // Setup merge policy
> TieredMergePolicy tieredMergePolicy = new TieredMergePolicy();
> SortingMergePolicy sortingMergePolicy = new
> SortingMergePolicy(tieredMergePolicy, sort);
> // Setup index writer
> IndexWriterConfig indexWriterConfig = new IndexWriterConfig(new
> SimpleAnalyzer());
> indexWriterConfig.setOpenMode(IndexWriterConfig.OpenMode.CREATE_OR_APPEND);
> indexWriterConfig.setMergePolicy(sortingMergePolicy);
> IndexWriter indexWriter = new IndexWriter(directory, indexWriterConfig);
> // Index values
> for (int i = 1; i <= 1000; i++) {
> Document document = new Document();
> document.add(new NumericDocValuesField(FIELD_NAME, i));
> indexWriter.addDocument(document);
> }
> // Force index merge to ensure early termination
> indexWriter.forceMerge(1, true);
> indexWriter.commit();
> // Create index searcher
> IndexReader reader = DirectoryReader.open(directory);
> IndexSearcher searcher = new IndexSearcher(reader);
> // Paginated read
> int pageSize = 10;
> FieldDoc pageStart = null;
> while (true) {
> logger.info("Collecting page starting at: {}", pageStart);
> Query query = new MatchAllDocsQuery();
> TopDocsCollector tfc = TopFieldCollector.create(sort, pageSize,
> pageStart, true, false, false);
> EarlyTerminatingSortingCollector collector = new
> EarlyTerminatingSortingCollector(tfc, sort, pageSize, sort);
> searcher.search(query, collector);
> ScoreDoc[] scoreDocs = tfc.topDocs().scoreDocs;
> for (ScoreDoc scoreDoc : scoreDocs) {
> pageStart = (FieldDoc) scoreDoc;
> logger.info("FOUND {}", scoreDoc);
> }
> logger.info("Terminated early: {}", collector.terminatedEarly());
> if (scoreDocs.length < pageSize) break;
> }
> // Close
> reader.close();
> indexWriter.close();
> directory.close();
> {code}
> The query for the second page doesn't return any results. However, it gets
> the expected results when if we don't wrap the {{TopFieldCollector}} with the
> {{EarlyTerminatingSortingCollector}}.
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