ElasticSearch
Sorting and Relevance
http://elastic.openthinklabs.com/

Sorting
GET /_search
{
"query" : {
"bool" : {
"filter" : {
"term" : {
"user_id" : 1
}
}
}
}
}
GET /_search
{
"query" : {
"constant_score" : {
"filter" : {
"term" : {
"user_id" : 1
}
}
}
}
}

Sorting
Sorting by Field Values
GET /_search
{
"query" : {
"bool" : {
"filter" : { "term" : { "user_id" : 1 }}
}
},
"sort": { "date": { "order": "desc" }}
}
"hits" : {
"total" : 6,
"max_score" : null,
"hits" : [ {
"_index" : "us",
"_type" : "tweet",
"_id" : "14",
"_score" : null,
"_source" : {
"date": "2014-09-24",
...
},
"sort" : [ 1411516800000 ]
},
...
}

Sorting
Multilevel Sorting
GET /_search
{
"query" : {
"bool" : {
"must": { "match": { "tweet": "manage text
search" }},
"filter" : { "term" : { "user_id" : 2 }}
}
},
"sort": [
{ "date": { "order": "desc" }},
{ "_score": { "order": "desc" }}
]
}

Sorting
Multilevel Sorting
GET /_search
{
"query" : {
"bool" : {
"must": { "match": { "tweet": "manage text
search" }},
"filter" : { "term" : { "user_id" : 2 }}
}
},
"sort": [
{ "date": { "order": "desc" }},
{ "_score": { "order": "desc" }}
]
}

Sorting
Sorting on Multivalue Fields
"sort": {
"dates": {
"order": "asc",
"mode": "min"
}
}

String Sorting and Multifields
"tweet": {
"type":
"string",
"analyzer":
"english"
}
"tweet": {
"type": "string",
"analyzer":
"english",
"fields": {
"raw": {
"type":
"string",
"index":
"not_analyzed"
}
}
}
GET /_search
{
"query": {
"match": {
"tweet":
"elasticsearch"
}
},
"sort": "tweet.raw"
}

What Is Relevance?
● The standard similarity algorithm used in Elasticsearch :
● Term frequency : How often does the term appear in the
field? The more often, the more relevant. A field containing
five mentions of the same term is more likely to be relevant
than a field containing just one mention.
● Inverse document frequency : How often does each term
appear in the index? The more often, the less relevant.
Terms that appear in many documents have a lower weight
than more-uncommon terms.
● Field-length norm : How long is the field? The longer it is,
the less likely it is that words in the field will be relevant. A
term appearing in a short title field carries more weight than
the same term appearing in a long content field

What Is Relevance?
Understanding the Score
GET /_search?explain
{
"query" : { "match" : { "tweet" :
"honeymoon" }}
}

What Is Relevance?
Understanding Why a Document Matched
GET /us/tweet/12/_explain
{
"query" : {
"bool" : {
"filter" : { "term" : { "user_id" : 2 }},
"must" : { "match" : { "tweet" : "honeymoon" }}
}
}
}
"failure to match filter: cache(user_id:[2 TO 2])"

Doc Values Intro
● Doc values are used in several places in
Elasticsearch:
● Sorting on a field
● Aggregations on a field
● Certain filters (for example, geolocation filters)
● Scripts that refer to fields

Referensi
● ElasticSearch, The Definitive Guide, A Distrib
uted Real-Time Search and Analytics Engine, Cl
inton Gormely & Zachary Tong, O’Reilly