Fixing JDK-11 and HighlighterSearchIT::testPostingsHighlighter

[reta]

Signed-off-by: Andriy Redko andriy.redko@aiven.io

Description

Fixing JDK-11 and HighlighterSearchIT::testPostingsHighlighter

Issues Resolved

[List any issues this PR will resolve]

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• Commits are signed per the DCO using --signoff

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[reta]

@nknize for HighlighterSearchIT::testWithNestedQuery (and very likely all other), there is more profound issue. The problem is related to org.opensearch.index.cache.bitset.BitsetFilterCache:

    private BitSet getAndLoadIfNotPresent(final Query query, final LeafReaderContext context) throws ExecutionException {
        final IndexReader.CacheHelper cacheHelper = context.reader().getCoreCacheHelper();
        if (cacheHelper == null) {
            throw new IllegalArgumentException("Reader " + context.reader() + " does not support caching");
        }
     ...
    }

The UnifiedHighlighter uses MemoryIndexOffsetStrategy with OverlaySingleDocTermsLeafReader as the LeafReaderContext, and this guy has no caching support:

public class OverlaySingleDocTermsLeafReader extends FilterLeafReader {
 ...
  @Override
  public CacheHelper getCoreCacheHelper() {
    return null;
  }

  @Override
  public CacheHelper getReaderCacheHelper() {
    return null;
  }
}

I don't have solution for now, looking into it (if you have please feel free to share). I found the solution but Opensearch Highlighters do not work properly with new HighlightFlag.WEIGHT_MATCHES, introduced by https://issues.apache.org/jira/browse/LUCENE-9431. This could be part of opensearch-project#2063

[nknize]

nice! thx for taking care of this one!