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Completion Suggester
editCompletion Suggester
editIn order to understand the format of suggestions, please read the Suggesters page first.
The completion
suggester is a so-called prefix suggester. It does not
do spell correction like the term
or phrase
suggesters but allows
basic auto-complete
functionality.
Why another suggester? Why not prefix queries?
editThe first question which comes to mind when reading about a prefix suggestion is, why you should use it at all, if you have prefix queries already. The answer is simple: Prefix suggestions are fast.
The data structures are internally backed by Lucenes
AnalyzingSuggester
, which uses FSTs (finite state transducers) to
execute suggestions. Usually these data structures are costly to
create, stored in-memory and need to be rebuilt every now and then to
reflect changes in your indexed documents. The completion
suggester
circumvents this by storing the FST (finite state transducer) as part
of your index during index time. This allows for really fast
loads and executions.
Mapping
editIn order to use this feature, you have to specify a special mapping for this field, which enables the special storage of the field.
curl -X PUT localhost:9200/music curl -X PUT localhost:9200/music/song/_mapping -d '{ "song" : { "properties" : { "name" : { "type" : "string" }, "suggest" : { "type" : "completion", "analyzer" : "simple", "search_analyzer" : "simple", "payloads" : true } } } }'
Mapping supports the following parameters:
-
analyzer
-
The index analyzer to use, defaults to
simple
. In case you are wondering why we did not opt for thestandard
analyzer: We try to have easy to understand behaviour here, and if you index the field contentAt the Drive-in
, you will not get any suggestions fora
, nor ford
(the first non stopword). -
search_analyzer
-
The search analyzer to use, defaults to value of
analyzer
. -
payloads
-
Enables the storing of payloads, defaults to
false
-
preserve_separators
-
Preserves the separators, defaults to
true
. If disabled, you could find a field starting withFoo Fighters
, if you suggest forfoof
. -
preserve_position_increments
-
Enables position increments, defaults
to
true
. If disabled and using stopwords analyzer, you could get a field starting withThe Beatles
, if you suggest forb
. Note: You could also achieve this by indexing two inputs,Beatles
andThe Beatles
, no need to change a simple analyzer, if you are able to enrich your data. -
max_input_length
-
Limits the length of a single input, defaults to
50
UTF-16 code points. This limit is only used at index time to reduce the total number of characters per input string in order to prevent massive inputs from bloating the underlying datastructure. The most usecases won’t be influenced by the default value since prefix completions hardly grow beyond prefixes longer than a handful of characters. (Old name "max_input_len" is deprecated)
Indexing
editcurl -X PUT 'localhost:9200/music/song/1?refresh=true' -d '{ "name" : "Nevermind", "suggest" : { "input": [ "Nevermind", "Nirvana" ], "output": "Nirvana - Nevermind", "payload" : { "artistId" : 2321 }, "weight" : 34 } }'
The following parameters are supported:
-
input
- The input to store, this can be a an array of strings or just a string. This field is mandatory.
-
output
-
The string to return, if a suggestion matches. This is very
useful to normalize outputs (i.e. have them always in the format
artist - songname
). This is optional. Note: The result is de-duplicated if several documents have the same output, i.e. only one is returned as part of the suggest result. -
payload
-
An arbitrary JSON object, which is simply returned in the
suggest option. You could store data like the id of a document, in order
to load it from elasticsearch without executing another search (which
might not yield any results, if
input
andoutput
differ strongly). -
weight
- A positive integer or a string containing a positive integer, which defines a weight and allows you to rank your suggestions. This field is optional.
Even though you will lose most of the features of the completion suggest, you can choose to use the following shorthand form. Keep in mind that you will not be able to use several inputs, an output, payloads or weights. This form does still work inside of multi fields.
{ "suggest" : "Nirvana" }
The suggest data structure might not reflect deletes on
documents immediately. You may need to do an Optimize for that.
You can call optimize with the only_expunge_deletes=true
to only target
deletions for merging. By default only_expunge_deletes=true
will only select
segments for merge where the percentage of deleted documents is greater than 10%
of
the number of document in that segment. To adjust this index.merge.policy.expunge_deletes_allowed
can
be updated to a value between [0..100]
. Please remember even with this option set, optimize
is considered a extremely heavy operation and should be called rarely.
Querying
editSuggesting works as usual, except that you have to specify the suggest
type as completion
.
curl -X POST 'localhost:9200/music/_suggest?pretty' -d '{ "song-suggest" : { "text" : "n", "completion" : { "field" : "suggest" } } }' { "_shards" : { "total" : 5, "successful" : 5, "failed" : 0 }, "song-suggest" : [ { "text" : "n", "offset" : 0, "length" : 1, "options" : [ { "text" : "Nirvana - Nevermind", "score" : 34.0, "payload" : {"artistId":2321} } ] } ] }
As you can see, the payload is included in the response, if configured
appropriately. If you configured a weight for a suggestion, this weight
is used as score
. Also the text
field uses the output
of your
indexed suggestion, if configured, otherwise the matched part of the
input
field.
The basic completion suggester query supports the following two parameters:
-
field
- The name of the field on which to run the query (required).
-
size
-
The number of suggestions to return (defaults to
5
).
The completion suggester considers all documents in the index. See Context Suggester for an explanation of how to query a subset of documents instead.
Fuzzy queries
editThe completion suggester also supports fuzzy queries - this means, you can actually have a typo in your search and still get results back.
curl -X POST 'localhost:9200/music/_suggest?pretty' -d '{ "song-suggest" : { "text" : "n", "completion" : { "field" : "suggest", "fuzzy" : { "fuzziness" : 2 } } } }'
The fuzzy query can take specific fuzzy parameters. The following parameters are supported:
|
The fuzziness factor, defaults to |
|
if set to |
|
Minimum length of the input before fuzzy
suggestions are returned, defaults |
|
Minimum length of the input, which is not
checked for fuzzy alternatives, defaults to |
|
Sets all are measurements (like edit distance, transpositions and lengths) in unicode code points (actual letters) instead of bytes. |
If you want to stick with the default values, but
still use fuzzy, you can either use fuzzy: {}
or fuzzy: true
.