批量请求

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.