Mappings: Deprecate index_name and path

[jpountz]

Today we allow for custom index names. This adds ambiguity as fields might be referred to either according to their index name or their field name. What should happen when several fields have the same index name or if the index name of a field is the same as the full name of another field?

My understanding is that custom index_names are not useful anymore now that we have copy_to in order to index several logical fields into a single physical one, so I'd like to deprecate custom index_names so that the index name would always be the same as the full name.

Relates to #4081, #8870

[clintongormley]

++

[s1monw]

huge +1 IMO we should start rejecting this setting on new created indices!

[dakrone]

Yes! Deprecate in 1.3 and remove in master?

[s1monw]

the removal is a problem IMO since this is a index level BWC issue :/

[clintongormley]

The index_name and path parameters are no longer needed now that we have copy_to. From 2.0, we should:

• refuse to create new indices which contain these mappings
• maintain the ability to understand index_name and path on existing indices
• change the upgrade API to complain about the use of deprecated params (see Upgrade API should also migrate index settings/mappings #8682)

From 3.0:

• remove index_name and path completely

[InfinitiesLoop]

For your consideration, please review this issue. Perhaps removing index_name will have a greater impact than intended.
#8980

[clintongormley]

In 2.0, I think we can upgrade the mapping in a way that is not perfect, but will cover most use cases and help users to upgrade without reindexing.

index_name and path are used for two main purposes:

• the old way to do copy_to
• provide fieldname aliases, eg tag points to tags

We can't distinguish between these two use cases automatically, but we can handle the first use case gracefully, and the second use case is an easy change to make application side (ie just change all use of tags to tag in searches)

A mapping that looks like this (with path set to just_name):

{
  "mappings": {
    "test": {
      "properties": {
        "name": {
          "type": "object",
          "path": "just_name", 
          "properties": {
            "first": {
              "type": "string",
              "index_name": "fullname"
            },
            "last": {
              "type": "string",
              "index_name": "fullname"
            }
          }
        }
      }
    }
  }
}

could be rewritten to:

{
  "mappings": {
    "test": {
      "properties": {
        "fullname": {
          "type": "string"
        },
        "name": {
          "type": "object",
          "properties": {
            "first": {
              "index": "no",
              "copy_to": "fullname"
            },
            "last": {
              "index": "no",
              "copy_to": "fullname"
            }
          }
        }
      }
    }
  }
}

The mapping for the new fullname field can just be the same as the mapping of the first field which uses index_name (without the index_name) setting. The original field will not be indexed (or searchable).

In the case where path is set to full, the same rules apply, but the new field uses the full path name, ie this:

{
  "mappings": {
    "test": {
      "properties": {
        "name": {
          "type": "object",
          "path": "full", 
          "properties": {
            "first": {
              "type": "string",
              "index_name": "fullname"
            },
            "last": {
              "type": "string",
              "index_name": "fullname"
            }
          }
        }
      }
    }
  }
}

could be rewritten as:

{
  "mappings": {
    "test": {
      "properties": {
        "name": {
          "type": "object",
          "properties": {
            "first": {
              "index": "no",
              "copy_to": "name.fullname"
            },
            "last": {
              "index": "no",
              "copy_to": "name.fullname"
            },
            "fullname": {
              "type": "string"
            }
          }
        }
      }
    }
  }
}