38_Reducing_memory.asciidoc

Reducing Memory Usage

Each lat/lon pair requires 16 bytes of memory, memory that is in short supply. It needs this much memory in order to provide very accurate results. But as we have commented before, such exacting precision is seldom required.

You can reduce the amount of memory that is used by switching to a compressed fielddata format and by specifying how precise you need your geo-points to be. Even reducing precision to 1mm reduces memory usage by a third. A more realistic setting of 3m reduces usage by 62%, and 1km saves a massive 75%!

This setting can be changed on a live index with the update-mapping API:

POST /attractions/_mapping/restaurant
{
  "location": {
    "type": "geo_point",
    "fielddata": {
      "format":    "compressed",
      "precision": "1km" (1)
    }
  }
}

1. Each lat/lon pair will require only 4 bytes, instead of 16.

Alternatively, you can avoid using memory for geo-points altogether, either by using the technique described in [optimize-bounding-box], or by storing geo-points as doc values:

PUT /attractions
{
  "mappings": {
    "restaurant": {
      "properties": {
        "name": {
          "type": "string"
        },
        "location": {
          "type":       "geo_point",
          "doc_values": true (1)
        }
      }
    }
  }
}

1. Geo-points will not be loaded into memory, but instead stored on disk.

Mapping a geo-point to use doc values can be done only when the field is first created. There is a small performance cost in using doc values instead of fielddata, but with memory in such short supply, it is often worth doing.