71 lines
1.8 KiB
Plaintext
71 lines
1.8 KiB
Plaintext
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[[geohash]]
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=== `geohash`
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Geohashes are a form of lat/lon encoding which divides the earth up into
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a grid. Each cell in this grid is represented by a geohash string. Each
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cell in turn can be further subdivided into smaller cells which are
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represented by a longer string. So the longer the geohash, the smaller
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(and thus more accurate) the cell is.
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Because geohashes are just strings, they can be stored in an inverted
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index like any other string, which makes querying them very efficient.
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If you enable the `geohash` option, a `geohash` ``sub-field'' will be indexed
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as, eg `.geohash`. The length of the geohash is controlled by the
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<<geohash-precision,`geohash_precision`>> parameter.
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If the <<geohash-prefix,`geohash_prefix`>> option is enabled, the `geohash`
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option will be enabled automatically.
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For example:
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[source,js]
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--------------------------------------------------
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PUT my_index
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{
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"mappings": {
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"my_type": {
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"properties": {
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"location": {
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"type": "geo_point", <1>
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"geohash": true
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}
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}
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}
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}
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}
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PUT my_index/my_type/1
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{
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"location": {
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"lat": 41.12,
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"lon": -71.34
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}
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}
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GET my_index/_search?fielddata_fields=location.geohash <2>
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{
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"query": {
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"prefix": {
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"location.geohash": "drm3b" <3>
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}
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}
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}
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--------------------------------------------------
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// AUTOSENSE
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<1> A `location.geohash` field will be indexed for each geo-point.
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<2> The geohash can be retrieved with <<doc-values,`doc_values`>>.
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<3> A <<query-dsl-prefix-query,`prefix`>> query can find all geohashes which start with a particular prefix.
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[WARNING]
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============================================
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A `prefix` query on geohashes is expensive. Instead, consider using the
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<<geohash-prefix,`geohash_prefix`>> to pay the expense once at index time
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instead of on every query.
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============================================
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