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_routing
edit_routing
editThe routing field allows to control the _routing
aspect when indexing
data and explicit routing control is required.
store / index
editThe first thing the _routing
mapping does is to store the routing
value provided (store
set to true
) and index it (index
set to
not_analyzed
). The reason why the routing is stored by default is so
reindexing data will be possible if the routing value is completely
external and not part of the docs.
required
editAnother aspect of the _routing
mapping is the ability to define it as
required by setting required
to true
. This is very important to set
when using routing features, as it allows different APIs to make use of
it. For example, an index operation will be rejected if no routing value
has been provided (or derived from the doc). A delete operation will be
broadcasted to all shards if no routing value is provided and _routing
is required.
path
editDeprecated in 1.5.0.
The routing value can be provided as an external value when indexing
(and still stored as part of the document, in much the same way
_source
is stored). But, it can also be automatically extracted from
the index doc based on a path
. For example, having the following
mapping:
{ "comment" : { "_routing" : { "required" : true, "path" : "blog.post_id" } } }
Will cause the following doc to be routed based on the 111222
value:
{ "text" : "the comment text" "blog" : { "post_id" : "111222" } }
Note, using path
without explicit routing value provided required an
additional (though quite fast) parsing phase.
id uniqueness
editWhen indexing documents specifying a custom _routing
, the uniqueness
of the _id
is not guaranteed throughout all the shards that the index
is composed of. In fact, documents with the same _id
might end up in
different shards if indexed with different _routing
values.