MoreLikeThis and unified highlighter

Elastic Stack Elasticsearch
1

When I use an MLT query and the unified highlighter I don't get highlighting. It works with the plain highlighter. I was just wondering whether the unified highlighter isn't yet meant to work with specialised queries such as MLT yet- or whether this is a bug. I'm on ES 5.5.0

Cheers,
Phil

2

You are right, the unified highlighter does not handle MLT query correctly. The reason is that this highlighter rewrites query with an empty reader and the MLT query relies on index reader stats to build the Lucene query.
It works with the plain highlighter but only if you set min_doc_freq to 1 so it's also a problem for other highlighters.
Can you open an issue on github for this ? I am not sure if we'll be able to handle this query correctly but we should at least have an issue that explains why.

3

Thanks. Issue raised: https://github.com/elastic/elasticsearch/issues/26357

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