Today we require users to prepare their indices for split operations.
Yet, we can do this automatically when an index is created which would
make the split feature a much more appealing option since it doesn't have
any 3rd party prerequisites anymore.
This change automatically sets the number of routinng shards such that
an index is guaranteed to be able to split once into twice as many shards.
The number of routing shards is scaled towards the default shard limit per index
such that indices with a smaller amount of shards can be split more often than
larger ones. For instance an index with 1 or 2 shards can be split 10x
(until it approaches 1024 shards) while an index created with 128 shards can only
be split 3x by a factor of 2. Please note this is just a default value and users
can still prepare their indices with `index.number_of_routing_shards` for custom
splitting.
NOTE: this change has an impact on the document distribution since we are changing
the hash space. Documents are still uniformly distributed across all shards but since
we are artificually changing the number of buckets in the consistent hashign space
document might be hashed into different shards compared to previous versions.
This is a 7.0 only change.
`_search_shards`API today only returns aliases names if there is an alias
filter associated with one of them. Now it can be useful to see which aliases
have been expanded for an index given the index expressions. This change also includes non-filtering aliases even without a filtering alias being present.
Add indices and filter information to search shards api output
The search shards api returns info about which shards are going to be hit by executing a search with provided parameters: indices, routing, preference. Indices can also be aliases, which can also hold filters. The output includes an array of shards and a summary of all the nodes the shards are allocated on. This commit adds a new indices section to the search shards output that includes one entry per index, where each index can be associated with an optional filter in case the index was hit through a filtered alias.
This is relevant since we have moved parsing of alias filters to the coordinating node.
Relates to #20916
The `type` parameter has always been accepted by the search_shards api, probably to make the api and its urls the same as search. Truth is that the type never had any effect, it's been ignored from day one while accepting it may make users think that we actually do something with it.
This commit removes support for the type parameter from the REST layer and the Java API. Backwards compatibility is maintained on the transport layer though.
The new added serialization test also uncovered a bug in the java API where the `ClusterSearchShardsRequest` could be created with no arguments, but the indices were required to be not null otherwise the request couldn't be serialized as `writeTo` would throw NPE. Fixed by setting a default value (empty array) for indices.
Simon Willnauer
Luca Cavanna
Nik Everett
Clinton Gormley