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https://issues.apache.org/jira/browse/LUCENE-10518?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17524408#comment-17524408
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Adrien Grand commented on LUCENE-10518:
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I'm unsure of the value of the consistency checks on 8.x indices. My gut
feeling is that either users have created indices with consistent fields until
now, and they'll keep their indices consistent after 9.0, or they have created
indices with inconsistent fields and this consistency check is making upgrades
harder without helping much. I wonder if we should just disable the check on
8.x indices based on the index created version?
> FieldInfos consistency check can refuse to open Lucene 8 index
> --------------------------------------------------------------
>
> Key: LUCENE-10518
> URL: https://issues.apache.org/jira/browse/LUCENE-10518
> Project: Lucene - Core
> Issue Type: Bug
> Components: core/index
> Affects Versions: 8.10.1
> Reporter: Nhat Nguyen
> Priority: Major
>
> A field-infos consistency check introduced in Lucene 9 (LUCENE-9334) can
> refuse to open a Lucene 8 index. Lucene 8 can create a partial FieldInfo if
> hitting a non-aborting exception (for example [term is too
> long|https://github.com/apache/lucene-solr/blob/6a6484ba396927727b16e5061384d3cd80d616b2/lucene/core/src/java/org/apache/lucene/index/DefaultIndexingChain.java#L944])
> during processing fields of a document. We don't have this problem in Lucene
> 9 as we process fields in two phases with the [first
> phase|https://github.com/apache/lucene/blob/10ebc099c846c7d96f4ff5f9b7853df850fa8442/lucene/core/src/java/org/apache/lucene/index/IndexingChain.java#L589-L614]
> processing only FieldInfos.
> The issue can be reproduced with this snippet.
> {code:java}
> public void testWriteIndexOn8x() throws Exception {
> FieldType KeywordField = new FieldType();
> KeywordField.setTokenized(false);
> KeywordField.setOmitNorms(true);
> KeywordField.setIndexOptions(IndexOptions.DOCS);
> KeywordField.freeze();
> try (Directory dir = newDirectory()) {
> IndexWriterConfig config = new IndexWriterConfig();
> config.setCommitOnClose(false);
> config.setMergePolicy(NoMergePolicy.INSTANCE);
> try (IndexWriter writer = new IndexWriter(dir, config)) {
> // first segment
> writer.addDocument(new Document()); // an empty doc
> Document d1 = new Document();
> byte[] chars = new byte[IndexWriter.MAX_STORED_STRING_LENGTH + 1];
> Arrays.fill(chars, (byte) 'a');
> d1.add(new Field("field", new BytesRef(chars), KeywordField));
> d1.add(new BinaryDocValuesField("field", new BytesRef(chars)));
> expectThrows(IllegalArgumentException.class, () ->
> writer.addDocument(d1));
> writer.flush();
> // second segment
> Document d2 = new Document();
> d2.add(new Field("field", new BytesRef("hello world"), KeywordField));
> d2.add(new SortedDocValuesField("field", new BytesRef("hello world")));
> writer.addDocument(d2);
> writer.flush();
> writer.commit();
> // Check for doc values types consistency
> Map<String, DocValuesType> docValuesTypes = new HashMap<>();
> try(DirectoryReader reader = DirectoryReader.open(dir)){
> for (LeafReaderContext leaf : reader.leaves()) {
> for (FieldInfo fi : leaf.reader().getFieldInfos()) {
> DocValuesType current = docValuesTypes.putIfAbsent(fi.name,
> fi.getDocValuesType());
> if (current != null && current != fi.getDocValuesType()) {
> fail("cannot change DocValues type from " + current + " to " +
> fi.getDocValuesType() + " for field \"" + fi.name + "\"");
> }
> }
> }
> }
> }
> }
> }
> {code}
> I would like to propose to:
> - Backport the two-phase fields processing from Lucene9 to Lucene8. The patch
> should be small and contained.
> - Introduce an option in Lucene9 to skip checking field-infos consistency
> (i.e., behave like Lucene 8 when the option is enabled).
> /cc [~mayya] and [~jpountz]
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