Full-Text Search Explained - Philipp Krenn - Codemotion Rome 2017

Full-Text Search
Explained
Philipp Krenn @xeraa

Infrastructure | Developer Advocate

But I can do...
SELECT *
FROM my_table
WHERE my_text LIKE ‘%my_term%’

2. Features
Fuzziness, synonyms, scoring,...

Indexing
Stemming
http://snowballstem.org

https://cloud.elastic.co

---
version: '2'
services:
kibana:
image: docker.elastic.co/kibana/kibana:5.2.2
links:
- elasticsearch
ports:
- 5601:5601
elasticsearch:
image: docker.elastic.co/elasticsearch/elasticsearch:5.2.2
cap_add:
- IPC_LOCK
volumes:
- esdata1:/usr/share/elasticsearch/data
ports:
- 9200:9200
volumes:
esdata1:
driver: local

Example
These are not the droids you
are looking for.

html_strip Char Filter
These are not the droids you are looking
for.

standard Tokenizer
These are not the droids you are
looking for

lowercase Token Filter
these are not the droids you are
looking for

stop Token Filter
droids you looking

snowball Token Filter
droid you look

GET /_analyze
{
"analyzer": "english",
"text": "These are not the droids you are looking for."
}

{
"tokens": [
{
"token": "droid",
"start_offset": 18,
"end_offset": 24,
"type": "<ALPHANUM>",
"position": 4
},
{
"token": "you",
"start_offset": 25,
"end_offset": 28,
"position": 5
},
...
]
}

GET /_analyze
{
"char_filter": [
"html_strip"
],
"tokenizer": "standard",
"filter": [
"lowercase",
"stop",
"snowball"
],
"text": "These are not the droids you are looking for."
}

{
"tokens": [
{
"token": "droid",
"start_offset": 27,
"end_offset": 33,
"position": 4
},
{
"token": "you",
"start_offset": 34,
"end_offset": 37,
"position": 5
},
...
]
}

Stop Words
a an and are as at be but by for if in into is
it no not of on or such that the their then
there these they this to was will with
https://github.com/apache/lucene-solr/blob/master/lucene/
core/src/java/org/apache/lucene/analysis/standard/
StandardAnalyzer.java#L44-L50

Italian
Questi non sono i droidi che state
cercando.

GET /_analyze
{
"analyzer": "italian",
"text": "Questi non sono i droidi che state cercando."
}

{
"tokens": [
{
"token": "droid",
"start_offset": 18,
"end_offset": 24,
"position": 4
},
{
"token": "state",
"start_offset": 29,
"end_offset": 34,
"position": 6
},
...
]
}

Italian Stop Words
https://github.com/apache/lucene-solr/blob/master/lucene/
analysis/common/src/resources/org/apache/lucene/analysis/
snowball/italian_stop.txt

Italian with the English
Analyzer
questi non sono i droidi che
state cercand

Detecting Languages
https://github.com/spinscale/
elasticsearch-ingest-langdetect

Languages in 5.0
arabic, armenian, basque, brazilian, bulgarian, catalan, cjk,
czech, danish, dutch, english, ﬁnnish, french, galician, german,
greek, hindi, hungarian, indonesian, irish, italian, latvian,
lithuanian, norwegian, persian, portuguese, romanian, russian,
sorani, spanish, swedish, turkish, thai

Language Rules
English: Philipp's → philipp
French: l'église → eglis
German: äußerst → ausserst

Another Example
Obi-Wan never told you what happened to
your father.

Another Example
obi wan never told you what
happen your father

Another Example
No. I am your father.

Another Example
i am your father

Elasticsearch
Index, typ, mapping

Multi-Language Support
One language per index
One language per type
One language per ﬁeld

PUT /starwars
{
"settings": {
"analysis": {
"filter": {
"my_synonym_filter": {
"type": "synonym",
"synonyms": [
"droid,machine",
"father,dad"
]
}
},

"analyzer": {
"my_analyzer": {
"char_filter": [
"html_strip"
],
"filter": [
"lowercase",
"stop",
"snowball",
"my_synonym_filter"
]
}
}
}
},

"mappings": {
"quotes": {
"properties": {
"quote": {
"type": "text",
"analyzer": "my_analyzer"
}
}
}
}
}

GET /starwars/_mapping
GET /starwars/_settings

PUT /starwars/quotes/1
{
"quote": "These are not the droids you are looking for."
}
{
"quote": "Obi-Wan never told you what happened to your father."
}
{
"quote": "No. I am your father."
}

GET /starwars/quotes/1
GET /starwars/quotes/1/_source

Inverted Index
ID 1 ID 2 ID 3
am 0 0 1[2]
droid 1[4] 0 0
father 0 1[9] 1[4]
happen 0 1[6] 0
i 0 0 1[1]
look 1[7] 0 0
never 0 1[2] 0
obi 0 1[0] 0
told 0 1[3] 0
wan 0 1[1] 0
what 0 1[5] 0
you 1[5] 1[4] 0
your 0 1[8] 1[3]

POST /starwars/_search
{
"query": {
"match_all": { }
}
}

{
"took": 1,
"timed_out": false,
"_shards": {
"total": 5,
"successful": 5,
"failed": 0
},
"hits": {
"total": 3,
"max_score": 1,
"hits": [
{
"_index": "starwars",
"_type": "my_type",
"_id": "2",
"_score": 1,
"_source": {
}
},
...

{
"query": {
"match": {
"quote": "droid"
}
}
}

{
"took": 2,
"timed_out": false,
"_shards": {
"total": 5,
"successful": 5,
"failed": 0
},
"hits": {
"total": 1,
"max_score": 0.39556286,
"hits": [
{
"_type": "quotes",
"_id": "1",
"_score": 0.39556286,
"_source": {
"quote": "These are not the droids you are looking for."
}
}
]
}
}

{
"query": {
"match": {
"quote": "dad"
}
}
}

...
"hits": {
"total": 2,
"max_score": 0.41913947,
"hits": [
{
"_type": "quotes",
"_id": "3",
"_score": 0.41913947,
"_source": {
}
},
{
"_type": "quotes",
"_id": "2",
"_score": 0.39291072,
"_source": {
}
}
]
}
}

{
"query": {
"match_phrase": {
"quote": "I am your father"
}
}
}

{
"took": 3,
"timed_out": false,
"_shards": {
"total": 5,
"successful": 5,
"failed": 0
},
"hits": {
"total": 1,
"max_score": 1.5665855,
"hits": [
{
"_type": "quotes",
"_id": "3",
"_score": 1.5665855,
"_source": {
}
}
]
}
}

{
"query": {
"match_phrase": {
"quote": "I am not your father"
}
}
}

{
"took": 15,
"timed_out": false,
"_shards": {
"total": 5,
"successful": 5,
"failed": 0
},
"hits": {
"total": 0,
"max_score": null,
"hits": []
}
}

{
"query": {
"match_phrase": {
"quote": {
"query": "I am not your father",
"slop": 1
}
}
}
}

{
"took": 5,
"timed_out": false,
"_shards": {
"total": 5,
"successful": 5,
"failed": 0
},
"hits": {
"total": 1,
"max_score": 1.0409548,
"hits": [
{
"_type": "quotes",
"_id": "3",
"_score": 1.0409548,
"_source": {
}
}
]
}
}

{
"query": {
"match": {
"quote": {
"query": "van",
"fuzziness": "AUTO"
}
}
}
}

{
"took": 14,
"timed_out": false,
"_shards": {
"total": 5,
"successful": 5,
"failed": 0
},
"hits": {
"total": 1,
"max_score": 0.18155496,
"hits": [
{
"_type": "quotes",
"_id": "2",
"_score": 0.18155496,
"_source": {
}
}
]
}
}

{
"query": {
"match": {
"quote": {
"query": "ovi-van",
"fuzziness": 1
}
}
}
}

{
"took": 109,
"timed_out": false,
"_shards": {
"total": 5,
"successful": 5,
"failed": 0
},
"hits": {
"total": 1,
"max_score": 0.3798467,
"hits": [
{
"_type": "quotes",
"_id": "2",
"_score": 0.3798467,
"_source": {
}
}
]
}
}

FuzzyQuery History
http://blog.mikemccandless.com/2011/03/lucenes-fuzzyquery-is-100-times-faster.html
Before: Brute force
Now: Levenshtein Automaton

http://blog.notdot.net/2010/07/Damn-Cool-Algorithms-Levenshtein-Automata

SELECT *
FROM starwars
WHERE quote LIKE "?an" OR
quote LIKE "V?n" OR
quote LIKE "Va?"

Term Frequency /
Inverse Document
Frequency (TF/IDF)
Search one term

BM25
Default in Elasticsearch 5.0
https://speakerdeck.com/elastic/improved-text-scoring-with-
bm25

Putting it Together
score(q,d) =
queryNorm(q)
· coord(q,d)
· ∑ (
tf(t in d)
· idf(t)²
· t.getBoost()
· norm(t,d)
) (t in q)

POST /starwars/_search?explain
{
"query": {
"match": {
"quote": "father"
}
}
}

...
"_explanation": {
"value": 0.41913947,
"description": "weight(Synonym(quote:dad quote:father) in 0) [PerFieldSimilarity], result of:",
"details": [
{
"value": 0.41913947,
"description": "score(doc=0,freq=2.0 = termFreq=2.0n), product of:",
"details": [
{
"value": 0.2876821,
"description": "idf(docFreq=1, docCount=1)",
"details": []
},
{
"value": 1.4569536,
"description": "tfNorm, computed from:",
"details": [
{
"value": 2,
"description": "termFreq=2.0",
"details": []
},
...

Score
0.41913947: i am your father
0.39291072: obi wan never told you
what happen your father

Vector Space Model
Search multiple terms

Score each term
Vectorize
Calculate angle

Function Score
Script, weight, random, ﬁeld value, decay
(geo or date)

{
"query": {
"function_score": {
"query": {
"match": {
"quote": "father"
}
},
"random_score": {}
}
}
}

Indexing
Formatting
Tokenize
Lowercase, Stop Words, Stemming
Synonyms

Scoring
Term Frequency
Inverse Document Frequency
Field-Length Norm
Vector Space Model

Grazie!
Questions?
Philipp Krenn @xeraa
PS: Stickers

{
"query": {
"match": {
"quote": "father"
}
},
"highlight": {
"pre_tags": [
"<tag>"
],
"post_tags": [
"</tag>"
],
"fields": {
"quote": {}
}
}
}

...
"hits": [
{
"_type": "quotes",
"_id": "3",
"_score": 0.41913947,
"_source": {
},
"highlight": {
"quote": [
"No. I am your <tag>father</tag>."
]
}
},
...

Boolean Queries
must must_not should filter

{
"query": {
"bool": {
"must": {
"match": {
"quote": {
"query": "father"
}
}
},
"should": [
{
"match": {
"quote": {
"query": "your"
}
}
},
{
"match": {
"quote": {
"query": "obi"
}
}
}
]
}
}
}

...
"hits": {
"total": 2,
"max_score": 0.96268076,
"hits": [
{
"_type": "quotes",
"_id": "2",
"_score": 0.96268076,
"_source": {
}
},
{
"_type": "quotes",
"_id": "3",
"_score": 0.73245656,
"_source": {
}
}
]
}
}

{
"query": {
"bool": {
"filter": {
"match": {
"quote": {
"query": "father"
}
}
},
"should": [
{
"match": {
"quote": {
"query": "your"
}
}
},
{
"match": {
"quote": {
"query": "obi"
}
}
}
]
}
}
}

...
"hits": {
"total": 2,
"max_score": 0.56977004,
"hits": [
{
"_type": "quotes",
"_id": "2",
"_score": 0.56977004,
"_source": {
}
},
{
"_type": "quotes",
"_id": "3",
"_score": 0.31331712,
"_source": {
}
}
]
}
}

{
"query": {
"bool": {
"must": {
"match": {
"quote": {
"query": "father"
}
}
},
"should": [
{
"match": {
"quote": {
"query": "your"
}
}
},
{
"match": {
"quote": {
"query": "obi"
}
}
},
{
"match": {
"quote": {
"query": "droid"
}
}
}
],
"minimum_number_should_match": 2
}
}
}

...
"hits": {
"total": 1,
"max_score": 0.96268076,
"hits": [
{
"_type": "quotes",
"_id": "2",
"_score": 0.96268076,
"_source": {
}
}
]
}
}

Boosting
Default 1 — greater or smaller

{
"query": {
"bool": {
"must": {
"match": {
"quote": {
"query": "father"
}
}
},
"should": [
{
"match": {
"quote": {
"query": "your"
}
}
},
{
"match": {
"quote": {
"query": "obi",
"boost": 3
}
}
}
]
}
}
}

...
"hits": {
"total": 2,
"max_score": 1.5324509,
"hits": [
{
"_type": "quotes",
"_id": "2",
"_score": 1.5324509,
"_source": {
}
},
{
"_type": "quotes",
"_id": "3",
"_score": 0.73245656,
"_source": {
}
}
]
}
}

Suggestion
Suggest a similar text
_search end point
_suggest deprecated

{
"query": {
"match": {
"quote": "fath"
}
},
"suggest": {
"my_suggestion" : {
"text" : "drui",
"term" : {
"field" : "quote"
}
}
}
}

...
"hits": {
"total": 0,
"max_score": null,
"hits": []
},
"suggest": {
"my_suggestion": [
{
"text": "drui",
"offset": 0,
"length": 4,
"options": [
{
"text": "droid",
"score": 0.5,
"freq": 1
}
]
}
]
}
}

NGram
Partial matches
Trigram
Edge Gram

GET /_analyze
{
"char_filter": [
"html_strip"
],
"tokenizer": {
"type": "ngram",
"min_gram": "3",
"max_gram": "3",
"token_chars": [
"letter"
]
},
"filter": [
"lowercase"
],
}

{
"tokens": [
{
"token": "the",
"start_offset": 0,
"end_offset": 3,
"type": "word",
"position": 0
},
{
"token": "hes",
"start_offset": 1,
"end_offset": 4,
"type": "word",
"position": 1
},
{
"token": "ese",
"start_offset": 2,
"end_offset": 5,
"type": "word",
"position": 2
},
{
"token": "are",
"start_offset": 6,
"end_offset": 9,
"type": "word",
"position": 3
},
...

GET /_analyze
{
"char_filter": [
"html_strip"
],
"tokenizer": {
"type": "edge_ngram",
"min_gram": "1",
"max_gram": "3",
"token_chars": [
"letter"
]
},
"filter": [
"lowercase"
],
}

{
"tokens": [
{
"token": "t",
"start_offset": 0,
"end_offset": 1,
"type": "word",
"position": 0
},
{
"token": "th",
"start_offset": 0,
"end_offset": 2,
"type": "word",
"position": 1
},
{
"token": "the",
"start_offset": 0,
"end_offset": 3,
"type": "word",
"position": 2
},
{
"token": "a",
"start_offset": 6,
"end_offset": 7,
"type": "word",
"position": 3
},
{
"token": "ar",
"start_offset": 6,
"end_offset": 8,
"type": "word",
"position": 4
},
...

Combining Analyzers
Reindex
Store multiple times
Combine scores

PUT /starwars_extended
{
"settings": {
"analysis": {
"filter": {
"my_synonym_filter": {
"type": "synonym",
"synonyms": [
"droid,machine",
"father,dad"
]
},
"my_ngram_filter": {
"type": "ngram",
"min_gram": "3",
"max_gram": "3",
"token_chars": [
"letter"
]
}
},

"analyzer": {
"my_lowercase_analyzer": {
"char_filter": [
"html_strip"
],
"tokenizer": "whitespace",
"filter": [
"lowercase"
]
},
"my_full_analyzer": {
"char_filter": [
"html_strip"
],
"filter": [
"lowercase",
"stop",
"snowball",
"my_synonym_filter"
]
},

"my_ngram_analyzer": {
"char_filter": [
"html_strip"
],
"filter": [
"lowercase",
"stop",
"my_ngram_filter"
]
}
}
}
},

"mappings": {
"quotes": {
"properties": {
"quote": {
"type": "text",
"fields": {
"lowercase": {
"type": "text",
"analyzer": "my_lowercase_analyzer"
},
"full": {
"type": "text",
"analyzer": "my_full_analyzer"
},
"ngram": {
"type": "text",
"analyzer": "my_ngram_analyzer"
}
}
}
}
}
}
}

POST /_reindex
{
"source": {
"index": "starwars"
},
"dest": {
"index": "starwars_extended"
}
}

POST /starwars_extended/_search?explain
{
"query": {
"multi_match": {
"query": "obiwan",
"fields": [
"quote",
"quote.lowercase",
"quote.full",
"quote.ngram"
],
"type": "most_fields"
}
}
}

...
"hits": {
"total": 1,
"max_score": 0.47685796,
"hits": [
{
"_shard": "[starwars_extended][2]",
"_node": "OsGbL-tZQJ-A8HO2PyDfhA",
"_index": "starwars_extended",
"_type": "quotes",
"_id": "2",
"_score": 0.47685796,
"_source": {
},
...

"weight(
Synonym(quote.ngram:biw quote.ngram:iwa quote.ngram:obi quote.ngram:wan)
in 0) [PerFieldSimilarity], result of:"

DELETE /starwars
DELETE /starwars_extended

Different Analyzers for
Indexing and Searching
Per query
In the mapping

GET /starwars_extended/_search
{
"query": {
"match": {
"quote.ngram": {
"query": "the",
"analyzer": "standard"
}
}
}
}

...
"hits": [
{
"_type": "quotes",
"_id": "2",
"_score": 0.38254172,
"_source": {
}
},
{
"_type": "quotes",
"_id": "3",
"_score": 0.36165747,
"_source": {
}
}
]
...

POST /starwars_extended/_close
PUT /starwars_extended/_settings
{
"analysis": {
"filter": {
"my_edgegram_filter": {
"type": "edge_ngram",
"min_gram": 1,
"max_gram": 10
}
},
"analyzer": {
"my_edgegram_analyzer": {
"char_filter": [
"html_strip"
],
"filter": [
"lowercase",
"my_edgegram_filter"
]
}
}
}
}
POST /starwars_extended/_open

PUT /starwars_extended/quotes/_mapping
{
"properties": {
"quote": {
"type": "text",
"fields": {
"edgegram": {
"type": "text",
"analyzer": "my_edgegram_analyzer",
"search_analyzer": "standard"
}
}
}
}
}

PUT /starwars_extended/quotes/4
{
"quote": "I find your lack of faith disturbing."
}
PUT /starwars_extended/quotes/5
{
"quote": "That... is why you fail."
}

POST /starwars_extended/_search
{
"query": {
"match": {
"quote.ngram": "faith"
}
}
}

...
"hits": [
{
"_type": "quotes",
"_id": "4",
"_score": 1.3019705,
"_source": {
}
},
{
"_type": "quotes",
"_id": "5",
"_score": 0.3812654,
"_source": {
"quote": "That... is why you fail."
}
}
]
...

POST /starwars_extended/_search
{
"query": {
"match": {
"quote.edgegram": "faith"
}
}
}

...
"hits": {
"total": 1,
"max_score": 0.41821626,
"hits": [
{
"_type": "quotes",
"_id": "4",
"_score": 0.41821626,
"_source": {
}
}
]
...

Image Credits
Schnitzel https://flic.kr/p/9m27wm
Architecture https://flic.kr/p/6dwCAe
Conchita https://flic.kr/p/nBqSHT

Full-Text Search Explained - Philipp Krenn - Codemotion Rome 2017

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