515 lines
20 KiB
Plaintext
515 lines
20 KiB
Plaintext
[[search-percolate]]
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== Percolator
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Traditionally you design documents based on your data, store them into an index, and then define queries via the search API
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in order to retrieve these documents. The percolator works in the opposite direction. First you store queries into an
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index and then, via the percolate API, you define documents in order to retrieve these queries.
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The reason that queries can be stored comes from the fact that in Elasticsearch both documents and queries are defined in
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JSON. This allows you to embed queries into documents via the index API. Elasticsearch can extract the query from a
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document and make it available to the percolate API. Since documents are also defined as JSON, you can define a document
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in a request to the percolate API.
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The percolator and most of its features work in realtime, so once a percolate query is indexed it can immediately be used
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in the percolate API.
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[IMPORTANT]
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=====================================
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Fields referred to in a percolator query must *already* exist in the mapping
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associated with the index used for percolation.
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There are two ways to make sure that a field mapping exist:
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* Add or update a mapping via the <<indices-create-index,create index>> or
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<<indices-put-mapping,put mapping>> APIs.
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* Percolate a document before registering a query. Percolating a document can
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add field mappings dynamically, in the same way as happens when indexing a
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document.
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=====================================
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[float]
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=== Sample Usage
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Create an index with a mapping for the field `message`:
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[source,js]
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--------------------------------------------------
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curl -XPUT 'localhost:9200/my-index' -d '{
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"mappings": {
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"my-type": {
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"properties": {
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"message": {
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"type": "string"
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}
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}
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}
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}
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}'
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--------------------------------------------------
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Register a query in the percolator:
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[source,js]
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--------------------------------------------------
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curl -XPUT 'localhost:9200/my-index/.percolator/1' -d '{
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"query" : {
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"match" : {
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"message" : "bonsai tree"
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}
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}
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}'
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--------------------------------------------------
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Match a document to the registered percolator queries:
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[source,js]
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--------------------------------------------------
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curl -XGET 'localhost:9200/my-index/my-type/_percolate' -d '{
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"doc" : {
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"message" : "A new bonsai tree in the office"
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}
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}'
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--------------------------------------------------
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The above request will yield the following response:
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[source,js]
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--------------------------------------------------
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{
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"took" : 19,
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"_shards" : {
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"total" : 5,
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"successful" : 5,
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"failed" : 0
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},
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"total" : 1,
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"matches" : [ <1>
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{
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"_index" : "my-index",
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"_id" : "1"
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}
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]
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}
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--------------------------------------------------
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<1> The percolate query with id `1` matches our document.
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[float]
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=== Indexing Percolator Queries
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Percolate queries are stored as documents in a specific format and in an arbitrary index under a reserved type with the
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name `.percolator`. The query itself is placed as is in a JSON object under the top level field `query`.
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[source,js]
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--------------------------------------------------
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{
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"query" : {
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"match" : {
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"field" : "value"
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}
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}
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}
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--------------------------------------------------
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Since this is just an ordinary document, any field can be added to this document. This can be useful later on to only
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percolate documents by specific queries.
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[source,js]
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--------------------------------------------------
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{
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"query" : {
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"match" : {
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"field" : "value"
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}
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},
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"priority" : "high"
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}
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--------------------------------------------------
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On top of this, also a mapping type can be associated with this query. This allows to control how certain queries
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like range queries, shape filters, and other query & filters that rely on mapping settings get constructed. This is
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important since the percolate queries are indexed into the `.percolator` type, and the queries / filters that rely on
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mapping settings would yield unexpected behaviour. Note: By default, field names do get resolved in a smart manner,
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but in certain cases with multiple types this can lead to unexpected behavior, so being explicit about it will help.
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[source,js]
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--------------------------------------------------
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{
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"query" : {
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"range" : {
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"created_at" : {
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"gte" : "2010-01-01T00:00:00",
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"lte" : "2011-01-01T00:00:00"
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}
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}
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},
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"type" : "tweet",
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"priority" : "high"
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}
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--------------------------------------------------
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In the above example the range query really gets parsed into a Lucene numeric range query, based on the settings for
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the field `created_at` in the type `tweet`.
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Just as with any other type, the `.percolator` type has a mapping, which you can configure via the mappings APIs.
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The default percolate mapping doesn't index the query field, only stores it.
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Because `.percolate` is a type it also has a mapping. By default the following mapping is active:
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[source,js]
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--------------------------------------------------
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{
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".percolator" : {
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"properties" : {
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"query" : {
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"type" : "object",
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"enabled" : false
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}
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}
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}
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}
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--------------------------------------------------
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If needed, this mapping can be modified with the update mapping API.
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In order to un-register a percolate query the delete API can be used. So if the previous added query needs to be deleted
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the following delete requests needs to be executed:
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[source,js]
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--------------------------------------------------
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curl -XDELETE localhost:9200/my-index/.percolator/1
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--------------------------------------------------
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[float]
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=== Percolate API
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The percolate API executes in a distributed manner, meaning it executes on all shards an index points to.
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.Required options
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* `index` - The index that contains the `.percolator` type. This can also be an alias.
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* `type` - The type of the document to be percolated. The mapping of that type is used to parse document.
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* `doc` - The actual document to percolate. Unlike the other two options this needs to be specified in the request body. Note: This isn't required when percolating an existing document.
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[source,js]
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--------------------------------------------------
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curl -XGET 'localhost:9200/twitter/tweet/_percolate' -d '{
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"doc" : {
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"created_at" : "2010-10-10T00:00:00",
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"message" : "some text"
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}
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}'
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--------------------------------------------------
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.Additional supported query string options
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* `routing` - In case the percolate queries are partitioned by a custom routing value, that routing option makes sure
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that the percolate request only gets executed on the shard where the routing value is partitioned to. This means that
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the percolate request only gets executed on one shard instead of all shards. Multiple values can be specified as a
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comma separated string, in that case the request can be be executed on more than one shard.
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* `preference` - Controls which shard replicas are preferred to execute the request on. Works the same as in the search API.
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* `ignore_unavailable` - Controls if missing concrete indices should silently be ignored. Same as is in the search API.
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* `percolate_format` - If `ids` is specified then the matches array in the percolate response will contain a string
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array of the matching ids instead of an array of objects. This can be useful to reduce the amount of data being send
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back to the client. Obviously if there are two percolator queries with same id from different indices there is no way
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to find out which percolator query belongs to what index. Any other value to `percolate_format` will be ignored.
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.Additional request body options
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* `filter` - Reduces the number queries to execute during percolating. Only the percolator queries that match with the
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filter will be included in the percolate execution. The filter option works in near realtime, so a refresh needs to have
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occurred for the filter to included the latest percolate queries.
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* `query` - Same as the `filter` option, but also the score is computed. The computed scores can then be used by the
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`track_scores` and `sort` option.
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* `size` - Defines to maximum number of matches (percolate queries) to be returned. Defaults to unlimited.
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* `track_scores` - Whether the `_score` is included for each match. The `_score` is based on the query and represents
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how the query matched the *percolate query's metadata*, *not* how the document (that is being percolated) matched
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the query. The `query` option is required for this option. Defaults to `false`.
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* `sort` - Define a sort specification like in the search API. Currently only sorting `_score` reverse (default relevancy)
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is supported. Other sort fields will throw an exception. The `size` and `query` option are required for this setting. Like
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`track_score` the score is based on the query and represents how the query matched to the percolate query's metadata
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and *not* how the document being percolated matched to the query.
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* `aggs` - Allows aggregation definitions to be included. The aggregations are based on the matching percolator queries,
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look at the aggregation documentation on how to define aggregations.
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* `highlight` - Allows highlight definitions to be included. The document being percolated is being highlight for each
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matching query. This allows you to see how each match is highlighting the document being percolated. See highlight
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documentation on how to define highlights. The `size` option is required for highlighting, the performance of highlighting
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in the percolate API depends of how many matches are being highlighted.
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[float]
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=== Dedicated Percolator Index
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Percolate queries can be added to any index. Instead of adding percolate queries to the index the data resides in,
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these queries can also be added to a dedicated index. The advantage of this is that this dedicated percolator index
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can have its own index settings (For example the number of primary and replica shards). If you choose to have a dedicated
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percolate index, you need to make sure that the mappings from the normal index are also available on the percolate index.
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Otherwise percolate queries can be parsed incorrectly.
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[float]
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=== Filtering Executed Queries
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Filtering allows to reduce the number of queries, any filter that the search API supports, (except the ones mentioned in important notes)
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can also be used in the percolate API. The filter only works on the metadata fields. The `query` field isn't indexed by
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default. Based on the query we indexed before, the following filter can be defined:
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[source,js]
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--------------------------------------------------
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curl -XGET localhost:9200/test/type1/_percolate -d '{
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"doc" : {
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"field" : "value"
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},
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"filter" : {
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"term" : {
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"priority" : "high"
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}
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}
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}'
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--------------------------------------------------
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[float]
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=== Percolator Count API
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The count percolate API, only keeps track of the number of matches and doesn't keep track of the actual matches
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Example:
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[source,js]
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--------------------------------------------------
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curl -XGET 'localhost:9200/my-index/my-type/_percolate/count' -d '{
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"doc" : {
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"message" : "some message"
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}
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}'
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--------------------------------------------------
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Response:
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[source,js]
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--------------------------------------------------
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{
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... // header
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"total" : 3
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}
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--------------------------------------------------
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[float]
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=== Percolating an Existing Document
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In order to percolate a newly indexed document, the percolate existing document can be used. Based on the response
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from an index request, the `_id` and other meta information can be used to immediately percolate the newly added
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document.
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.Supported options for percolating an existing document on top of existing percolator options:
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* `id` - The id of the document to retrieve the source for.
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* `percolate_index` - The index containing the percolate queries. Defaults to the `index` defined in the url.
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* `percolate_type` - The percolate type (used for parsing the document). Default to `type` defined in the url.
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* `routing` - The routing value to use when retrieving the document to percolate.
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* `preference` - Which shard to prefer when retrieving the existing document.
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* `percolate_routing` - The routing value to use when percolating the existing document.
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* `percolate_preference` - Which shard to prefer when executing the percolate request.
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* `version` - Enables a version check. If the fetched document's version isn't equal to the specified version then the request fails with a version conflict and the percolation request is aborted.
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Internally the percolate API will issue a GET request for fetching the `_source` of the document to percolate.
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For this feature to work, the `_source` for documents to be percolated needs to be stored.
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[float]
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==== Example
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Index response:
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[source,js]
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--------------------------------------------------
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{
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"_index" : "my-index",
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"_type" : "message",
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"_id" : "1",
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"_version" : 1,
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"created" : true
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}
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--------------------------------------------------
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Percolating an Existing Document:
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[source,js]
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--------------------------------------------------
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curl -XGET 'localhost:9200/my-index1/message/1/_percolate'
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--------------------------------------------------
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The response is the same as with the regular percolate API.
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[float]
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=== Multi Percolate API
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The multi percolate API allows to bundle multiple percolate requests into a single request, similar to what the multi
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search API does to search requests. The request body format is line based. Each percolate request item takes two lines,
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the first line is the header and the second line is the body.
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The header can contain any parameter that normally would be set via the request path or query string parameters.
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There are several percolate actions, because there are multiple types of percolate requests.
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.Supported actions:
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* `percolate` - Action for defining a regular percolate request.
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* `count` - Action for defining a count percolate request.
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Depending on the percolate action different parameters can be specified. For example the percolate and percolate existing
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document actions support different parameters.
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.The following endpoints are supported
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* `GET|POST /[index]/[type]/_mpercolate`
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* `GET|POST /[index]/_mpercolate`
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* `GET|POST /_mpercolate`
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The `index` and `type` defined in the url path are the default index and type.
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[float]
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==== Example
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Request:
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[source,js]
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--------------------------------------------------
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curl -XGET 'localhost:9200/twitter/tweet/_mpercolate' --data-binary @requests.txt; echo
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--------------------------------------------------
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The index `twitter` is the default index, and the type `tweet` is the default type and will be used in the case a header
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doesn't specify an index or type.
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requests.txt:
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[source,js]
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--------------------------------------------------
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{"percolate" : {"index" : "twitter", "type" : "tweet"}}
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{"doc" : {"message" : "some text"}}
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{"percolate" : {"index" : "twitter", "type" : "tweet", "id" : "1"}}
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{}
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{"percolate" : {"index" : "users", "type" : "user", "id" : "3", "percolate_index" : "users_2012" }}
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{"size" : 10}
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{"count" : {"index" : "twitter", "type" : "tweet"}}
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{"doc" : {"message" : "some other text"}}
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{"count" : {"index" : "twitter", "type" : "tweet", "id" : "1"}}
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{}
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--------------------------------------------------
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For a percolate existing document item (headers with the `id` field), the response can be an empty JSON object.
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All the required options are set in the header.
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Response:
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[source,js]
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--------------------------------------------------
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{
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"responses" : [
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{
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"took" : 24,
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"_shards" : {
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"total" : 5,
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"successful" : 5,
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"failed" : 0,
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},
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"total" : 3,
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"matches" : [
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{
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"_index": "twitter",
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"_id": "1"
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},
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{
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"_index": "twitter",
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"_id": "2"
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},
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{
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"_index": "twitter",
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"_id": "3"
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}
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]
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},
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{
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"took" : 12,
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"_shards" : {
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"total" : 5,
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"successful" : 5,
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"failed" : 0,
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},
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"total" : 3,
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"matches" : [
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{
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"_index": "twitter",
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"_id": "4"
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},
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{
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"_index": "twitter",
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"_id": "5"
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},
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{
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"_index": "twitter",
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"_id": "6"
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}
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]
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},
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{
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"error" : "DocumentMissingException[[_na][_na] [user][3]: document missing]"
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},
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{
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"took" : 12,
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"_shards" : {
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"total" : 5,
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"successful" : 5,
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"failed" : 0,
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},
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"total" : 3
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},
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{
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"took" : 14,
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"_shards" : {
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"total" : 5,
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"successful" : 5,
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"failed" : 0,
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},
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"total" : 3
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}
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]
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}
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--------------------------------------------------
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Each item represents a percolate response, the order of the items maps to the order in which the percolate requests
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were specified. In case a percolate request failed, the item response is substituted with an error message.
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[float]
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=== How it Works Under the Hood
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When indexing a document that contains a query in an index and the `.percolator` type, the query part of the documents gets
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parsed into a Lucene query and is kept in memory until that percolator document is removed or the index containing the
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`.percolator` type gets removed. So, all the active percolator queries are kept in memory.
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At percolate time, the document specified in the request gets parsed into a Lucene document and is stored in a in-memory
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Lucene index. This in-memory index can just hold this one document and it is optimized for that. Then all the queries
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that are registered to the index that the percolate request is targeted for, are going to be executed on this single document
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in-memory index. This happens on each shard the percolate request needs to execute.
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By using `routing`, `filter` or `query` features the amount of queries that need to be executed can be reduced and thus
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the time the percolate API needs to run can be decreased.
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[float]
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=== Important Notes
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Because the percolator API is processing one document at a time, it doesn't support queries and filters that run
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against child documents such as `has_child` and `has_parent`.
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The `inner_hits` feature on the `nested` query isn't supported in the percolate api.
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The `wildcard` and `regexp` query natively use a lot of memory and because the percolator keeps the queries into memory
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this can easily take up the available memory in the heap space. If possible try to use a `prefix` query or ngramming to
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achieve the same result (with way less memory being used).
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The delete-by-query API doesn't work to unregister a query, it only deletes the percolate documents from disk. In order
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to update the registered queries in memory the index needs be closed and opened.
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[float]
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=== Forcing Unmapped Fields to be Handled as Strings
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In certain cases it is unknown what kind of percolator queries do get registered, and if no field mapping exists for fields
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that are referred by percolator queries then adding a percolator query fails. This means the mapping needs to be updated
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to have the field with the appropriate settings, and then the percolator query can be added. But sometimes it is sufficient
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if all unmapped fields are handled as if these were default string fields. In those cases one can configure the
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`index.percolator.map_unmapped_fields_as_string` setting to `true` (default to `false`) and then if a field referred in
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a percolator query does not exist, it will be handled as a default string field so that adding the percolator query doesn't
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fail.
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