多文档模式

The patterns for the mget and bulk APIs are similar to those for
individual documents. The difference is that the requesting node knows in
which shard each document lives. It breaks up the multi-document request into
a multi-document request per shard, and forwards these in parallel to each
participating node.

Once it receives answers from each node, it collates their responses
into a single response, which it returns to the client.

[[img-distrib-mget]]
.Retrieving multiple documents with mget
image::images/04-05_mget.png[“Retrieving multiple documents with mget”]

Below we list the sequence of steps necessary to retrieve multiple documents
with a single mget request, as depicted in <>:

1. The client sends an mget request to Node_1.

2. Node 1 builds a multi-get request per shard, and forwards these
   requests in parallel to the nodes hosting each required primary or replica
   shard. Once all replies have been received, Node 1 builds the response
   and returns it to the client.

A routing parameter can be set for each document in the docs array,
and the preference parameter can be set for the top-level mget
request.

[[img-distrib-bulk]]
.Multiple document changes with bulk
image::images/04-06_bulk.png[“Multiple document changes with bulk”]

Below we list the sequence of steps necessary to execute multiple
create, index, delete and update requests within a single
bulk request, as depicted in <>:

1. The client sends a bulk request to Node_1.

2. Node 1 builds a bulk request per shard, and forwards these requests in
   parallel to the nodes hosting each involved primary shard.

3. The primary shard executes each action serially, one after another. As each
   action succeeds, the primary forwards the new document (or deletion) to its
   replica shards in parallel, then moves on to the next action. Once all
   replica shards report success for all actions, the node reports success to
   the requesting node, which collates the responses and returns them to the
   client.

The bulk API also accepts the replication and consistency parameters
at the top-level for the whole bulk request, and the routing parameter
in the metadata for each request.