Known limitations
Here is a summary of the known limitations:
-
A join query involving one or more runtime fields is currently supported using
HASH_JOIN
orBROADCAST_JOIN
algorithms. TheINDEX_JOIN
andROUTING_JOIN
algorithms only support joins with the runtime field on the child set. -
Regarding fields of
nested
type:-
The
join
filter within anested
query is currently not supported. -
A
nested
query within ajoin
filter is supported if and only if the join key does not refer to a field of the nested object. -
The projection of fields of the nested data type is only possible by using runtime fields. See Joining your data .
-
-
The projection of fields of runtime
lookup
data type is currently not supported. -
A
has_child
orhas_parent
query in a join query is supported, but a join query in ahas_child
orhas_parent
query is currently not supported. -
Regarding the
_id
field:-
The
_id
field is supported as a join key field with concrete indices, but its projection as a secondary field is not supported. When the_id
field is used as the join key on the child side, no other field can be projected. -
The
_id
field can only be projected as a secondary field using a script or runtime mapping. The script needs to access the stored field of Elasticsearch for the_id
, e.g.,params._fields._id.value
. This access pattern can be slow.
-
-
Spatial joins, as well as multi-conditional joins are limited to the
INDEX_JOIN
algorithm
Limitations specific to the ROUTING_JOIN
-
The
ROUTING_JOIN
cannot be selected when joining on something other than the parent set’s_id
. -
The
ROUTING_JOIN
must not be selected when the parent set’s indices use custom routing as this can result in incorrect joins.-
When using custom routing, the best practice is to declare the routing value as required in the index mapping, as per Elasticsearch’s documentation.
-
Following this best practice from Elasticsearch will also prevent incorrect join results to be generated inadvertently by Federate.
-
If this best practice is followed, Federate will prompt users with a meaningful error message when they select the
ROUTING JOIN
algorithm despite the custom routing on the parent set’s indices. -
If this best practice is followed, Federate’s query planner will never select the
ROUTING JOIN
in case of custom routing on the parent set’s indices.
-
-
-
The
ROUTING_JOIN
cannot be selected when the parent set’s indices are referred by some alias that uses custom routing for indexing (see Alias routing). -
The
ROUTING_JOIN
cannot be selected when the parent set is a data stream with propertyallow_custom_routing
set totrue
(see_routing
field).