This change removes the `postings` highlighter. This highlighter has been removed from Lucene master (7.x) because it behaves
exactly like the `unified` highlighter when index_options is set to `offsets`:
https://issues.apache.org/jira/browse/LUCENE-7815
It also makes the `unified` highlighter the default choice for highlighting a field (if `type` is not provided).
The strategy used internally by this highlighter remain the same as before, it checks `term_vectors` first, then `postings` and ultimately it re-analyzes the text.
Ultimately it rewrites the docs so that the options that the `unified` highlighter cannot handle are clearly marked as such.
There are few features that the `unified` highlighter is not able to handle which is why the other highlighters (`plain` and `fvh`) are still available.
I'll open separate issues for these features and we'll deprecate the `fvh` and `plain` highlighters when full support for these features have been added to the `unified`.
* Add support for fragment_length in the unified highlighter
This commit introduce a new break iterator (a BoundedBreakIterator) designed for the unified highlighter
that is able to limit the size of fragments produced by generic break iterator like `sentence`.
The `unified` highlighter now supports `boundary_scanner` which can `words` or `sentence`.
The `sentence` mode will use the bounded break iterator in order to limit the size of the sentence to `fragment_length`.
When sentences bigger than `fragment_length` are produced, this mode will break the sentence at the next word boundary **after**
`fragment_length` is reached.
This commit adds a boundary_scanner property to the search highlight
request so the user can specify different boundary scanners:
* `chars` (default, current behavior)
* `word` Use a WordBreakIterator
* `sentence` Use a SentenceBreakIterator
This commit also adds "boundary_scanner_locale" to define which locale
should be used when scanning the text.
* Integrate UnifiedHighlighter
This change integrates the Lucene highlighter called "unified" in the list of supported highlighters for ES.
This highlighter can extract offsets from either postings, term vectors, or via re-analyzing text.
The best strategy is picked automatically at query time and depends on the field and the query to highlight.
Previously, this doc was using a field called "content". This is
confusing, especially when the doc starts talking about the content of
the content field. This change makes the field name "comment" which
is less ambiguous and also changes some related field names in the doc
to make a consistent example theme of editing docs around blog posts.
Adds `warnings` syntax to the yaml test that allows you to expect
a `Warning` header that looks like:
```
- do:
warnings:
- '[index] is deprecated'
- quotes are not required because yaml
- but this argument is always a list, never a single string
- no matter how many warnings you expect
get:
index: test
type: test
id: 1
```
These are accessible from the docs with:
```
// TEST[warning:some warning]
```
This should help to force you to update the docs if you deprecate
something. You *must* add the warnings marker to the docs or the build
will fail. While you are there you *should* update the docs to add
deprecation warnings visible in the rendered results.
Rename `fields` to `stored_fields` and add `docvalue_fields`
`stored_fields` parameter will no longer try to retrieve fields from the _source but will only return stored fields.
`fields` will throw an exception if the user uses it.
Add `docvalue_fields` as an adjunct to `fielddata_fields` which is deprecated. `docvalue_fields` will try to load the value from the docvalue and fallback to fielddata cache if docvalues are not enabled on that field.
Closes#18943
`stored_fields` parameter will no longer try to retrieve fields from the _source but will only return stored fields.
`fields` will throw an exception if the user uses it.
Add `docvalue_fields` as an adjunct to `fielddata_fields` which is deprecated. `docvalue_fields` will try to load the value from the docvalue and fallback to fielddata cache if docvalues are not enabled on that field.
Closes#18943
We should prevent highlighting if a field is anything but a text or keyword field.
However, someone might implement a custom field type that has text and still want to
highlight on that. We cannot know in advance if the highlighter will be able to
highlight such a field and so we do the following:
If the field is only highlighted because the field matches a wildcard we assume
it was a mistake and do not process it.
If the field was explicitly given we assume that whoever issued the query knew
what they were doing and try to highlight anyway.
closes#17537
IMHO the original text here was incomplete. Adding the simple words 'in the index mapping' makes this sentence more clear. Perhaps a be more clear to make this a link.
The only way to refer to the plain highlighter is now `plain`, the only way to refer to the fast vector highlighter is `fvh` and the only way to refer to the postings highlighter is `postings`. The name variants like `highlighter`, `postings-highlighter` and `fast-vector-highlighter` have been removed.
The default `false` for `require_field_match` is a bit odd and confusing for users, given that field names get ignored by default and every field gets highlighted if it contains terms extracted out of the query, regardless of which fields were queries. Changed the default to `true`, it can always be changed per request.
Closes#10627Closes#11067
Our own fork of the lucene PostingsHighlighter is not easy to maintain and doesn't give us any added value at this point. In particular, it was introduced to support the require_field_match option and discrete per value highlighting, used in case one wants to highlight the whole content of a field, but get back one snippet per value. These two features won't
make it into lucene as they slow things down and shouldn't have been supported from day one on our end probably.
One other customization we had was support for a wider range of queries via custom rewrite etc. (yet another way to slow
things down), which got added to lucene and works much much better than what we used to do (instead of or rewrite, term
s are pulled out of the automata for multi term queries).
Removing our fork means the following in terms of features:
- dropped support for require_field_match: the postings highlighter will only highlight fields that were queried
- some custom es queries won't be supported anymore, meaning they won't be highlighted. The only one I found up until now is the phrase_prefix. Postings highlighter rewrites against an empty reader to avoid slow operations (like the ones that we were performing with the fork that we are removing here), thus the prefix will not be expanded to any term. What the postings highlighter does instead is pulling the automata out of multi term queries, but this is not supported at the moment with our MultiPhrasePrefixQuery.
Closes#10625Closes#11077
Because json objects are unordered this also adds an explicit order syntax
that looks like
"highlight": {
"fields": [
{"title":{ /*params*/ }},
{"text":{ /*params*/ }}
]
}
This is not useful for any of the builtin highlighters but will be useful
in plugins.
Closes#4649
In #4052 we added support for highlighting multi term queries using the postings highlighter. That worked only for top-level queries though, and not for multi term queries that are nested for instance within a bool query, or filtered query, or a constant score query.
The way we make this work is by walking the query structure and temporarily overriding the query rewrite method with a method that allows for multi terms extraction.
Closes#5102
The FVH was throwing away some boosts on queries stopping a number of
ways to boost phrase matches to the top of the list of fragments from
working.
The plain highlighter also doesn't work for this but that is because it
doesn't support the concept of the same term having a different score at
different positions.
Also update documentation claiming that FHV is nicer for weighing terms
found by query combinations.
Closes#4351
The percolator uses this option to deal with the fact that the MemoryIndex doesn't support stored fields,
this is possible b/c the _source of the document being percolated is always present.
Closes#4348
The Fast Vector Highlighter can combine matches on multiple fields to
highlight a single field using `matched_fields`. This is most
intuitive for multifields that analyze the same string in different
ways. Example:
{
"query": {
"query_string": {
"query": "content.plain:running scissors",
"fields": ["content"]
}
},
"highlight": {
"order": "score",
"fields": {
"content": {
"matched_fields": ["content", "content.plain"],
"type" : "fvh"
}
}
}
}
Closes#3750
Requires field index_options set to "offsets" in order to store positions and offsets in the postings list.
Considerably faster than the plain highlighter since it doesn't require to reanalyze the text to be highlighted: the larger the documents the better the performance gain should be.
Requires less disk space than term_vectors, needed for the fast_vector_highlighter.
Breaks the text into sentences and highlights them. Uses a BreakIterator to find sentences in the text. Plays really well with natural text, not quite the same if the text contains html markup for instance.
Treats the document as the whole corpus, and scores individual sentences as if they were documents in this corpus, using the BM25 algorithm.
Uses forked version of lucene postings highlighter to support:
- per value discrete highlighting for fields that have multiple values, needed when number_of_fragments=0 since we want to return a snippet per value
- manually passing in query terms to avoid calling extract terms multiple times, since we use a different highlighter instance per doc/field, but the query is always the same
The lucene postings highlighter api is quite different compared to the existing highlighters api, the main difference being that it allows to highlight multiple fields in multiple docs with a single call, ensuring sequential IO.
The way it is introduced in elasticsearch in this first round is a compromise trying not to change the current highlight api, which works per document, per field. The main disadvantage is that we lose the sequential IO, but we can always refactor the highlight api to work with multiple documents.
Supports pre_tag, post_tag, number_of_fragments (0 highlights the whole field), require_field_match, no_match_size, order by score and html encoding.
Closes#3704
You can configure the highlighting api to return an excerpt of a field
even if there wasn't a match on the field.
The FVH makes excerpts from the beginning of the string to the first
boundary character after the requested length or the boundary_max_scan,
whichever comes first. The Plain highlighter makes excerpts from the
beginning of the string to the end of the last token before the requested
length.
Closes#1171
Jim Ferenczi
Suhas Karanth
Nik Everett
Shai Erera
Clinton Gormley
Joshua Rich
Isabel Drost-Fromm
Britta Weber
Jeff
javanna
markharwood
Hannes Korte
Martijn van Groningen
Lee Hinman