对bulk request的处理流程：
1、遍历所有的request，对其做一些加工，主要包括：获取routing(如果mapping里有的话)、指定的timestamp(如果没有带timestamp会使用当前时间)，如果没有指定id字段，在action.bulk.action.allow_id_generation配置为true的情况下，会自动生成一个base64UUID作为id字段，并会将request的opType字段置为CREATE，因为如果是使用es自动生成的id的话，默认就是createdocument而不是updatedocument。（注：坑爹啊，我从github上面下的最新的ES代码，发现自动生成id这一段已经没有设置opType字段了，看起来和有指定id是一样的处理逻辑了，见https://github.com/elastic/elasticsearch/blob/master/core/src/main/java/org/elasticsearch/action/index/IndexRequest.java）。
2、创建一个shardId--> Operation的Map，再次遍历所有的request，获取获取每个request应该发送到的shardId，获取的过程是这样的：request有routing就直接返回，如果没有，会先对id求一个hash，这里的hash函数默认是Murmur3，当然你也可以通过配置index.legacy.routing.hash.type来决定使用的hash函数,决定发到哪个shard：
return MathUtils.mod(hash, indexMetaData.getNumberOfShards()); 注意：最新版ES代码已经改变！
即用hash对shard的总数求模来获取shardId，将shardId作为key，通过遍历的index和request组成BulkItemRequest的集合作为value放入之前说的map中（为什么要拿到遍历的index，因为在bulk response中可以看到对每个request的请求处理结果的），其实说了这么多就是要对request按shard来分组（为负载均衡）。
3、遍历上面得到的map，对不同的分组创建一个bulkShardRequest，包含配置consistencyLevel和timeout。并从集群state中获得primary shard，如果primary在本机就直接执行，如果不在会再发送到其shard所在的node。
源码位置：https://github.com/elastic/elasticsearch/blob/master/core/src/main/java/org/elasticsearch/action/bulk/TransportBulkAction.java
void executeBulk(Task task, final BulkRequest bulkRequest, final long startTimeNanos, final ActionListener<BulkResponse> listener, final AtomicArray<BulkItemResponse> responses ) {
final ClusterState clusterState = clusterService.state();
// TODO use timeout to wait here if its blocked...
clusterState.blocks().globalBlockedRaiseException(ClusterBlockLevel.WRITE);
final ConcreteIndices concreteIndices = new ConcreteIndices(clusterState, indexNameExpressionResolver);
MetaData metaData = clusterState.metaData();
for (int i = 0; i < bulkRequest.requests.size(); i++) {
DocWriteRequest docWriteRequest = bulkRequest.requests.get(i);
//the request can only be null because we set it to null in the previous step, so it gets ignored
if (docWriteRequest == null) {
continue;
}
if (addFailureIfIndexIsUnavailable(docWriteRequest, bulkRequest, responses, i, concreteIndices, metaData)) {
continue;
}
Index concreteIndex = concreteIndices.resolveIfAbsent(docWriteRequest);
try {
switch (docWriteRequest.opType()) {
case CREATE:
case INDEX:
IndexRequest indexRequest = (IndexRequest) docWriteRequest;
MappingMetaData mappingMd = null;
final IndexMetaData indexMetaData = metaData.index(concreteIndex);
if (indexMetaData != null) {
mappingMd = indexMetaData.mappingOrDefault(indexRequest.type());
}
indexRequest.resolveRouting(metaData);
indexRequest.process(mappingMd, allowIdGeneration, concreteIndex.getName());
break;
case UPDATE:
TransportUpdateAction.resolveAndValidateRouting(metaData, concreteIndex.getName(), (UpdateRequest) docWriteRequest);
break;
case DELETE:
TransportDeleteAction.resolveAndValidateRouting(metaData, concreteIndex.getName(), (DeleteRequest) docWriteRequest);
break;
default: throw new AssertionError("request type not supported: [" + docWriteRequest.opType() + "]");
}
} catch (ElasticsearchParseException | RoutingMissingException e) {
BulkItemResponse.Failure failure = new BulkItemResponse.Failure(concreteIndex.getName(), docWriteRequest.type(), docWriteRequest.id(), e);
BulkItemResponse bulkItemResponse = new BulkItemResponse(i, docWriteRequest.opType(), failure);
responses.set(i, bulkItemResponse);
// make sure the request gets never processed again
bulkRequest.requests.set(i, null);
}
}
// first, go over all the requests and create a ShardId -> Operations mapping
Map<ShardId, List<BulkItemRequest>> requestsByShard = new HashMap<>();
for (int i = 0; i < bulkRequest.requests.size(); i++) {
DocWriteRequest request = bulkRequest.requests.get(i);
if (request == null) {
continue;
}
String concreteIndex = concreteIndices.getConcreteIndex(request.index()).getName();
ShardId shardId = clusterService.operationRouting().indexShards(clusterState, concreteIndex, request.id(), request.routing()).shardId();
List<BulkItemRequest> shardRequests = requestsByShard.computeIfAbsent(shardId, shard -> new ArrayList<>());
shardRequests.add(new BulkItemRequest(i, request));
}
if (requestsByShard.isEmpty()) {
listener.onResponse(new BulkResponse(responses.toArray(new BulkItemResponse[responses.length()]), buildTookInMillis(startTimeNanos)));
return;
}
final AtomicInteger counter = new AtomicInteger(requestsByShard.size());
String nodeId = clusterService.localNode().getId();
for (Map.Entry<ShardId, List<BulkItemRequest>> entry : requestsByShard.entrySet()) {
final ShardId shardId = entry.getKey();
final List<BulkItemRequest> requests = entry.getValue();
BulkShardRequest bulkShardRequest = new BulkShardRequest(shardId, bulkRequest.getRefreshPolicy(),
requests.toArray(new BulkItemRequest[requests.size()]));
bulkShardRequest.waitForActiveShards(bulkRequest.waitForActiveShards());
bulkShardRequest.timeout(bulkRequest.timeout());
if (task != null) {
bulkShardRequest.setParentTask(nodeId, task.getId());
}
shardBulkAction.execute(bulkShardRequest, new ActionListener<BulkShardResponse>() {
@Override
public void onResponse(BulkShardResponse bulkShardResponse) {
for (BulkItemResponse bulkItemResponse : bulkShardResponse.getResponses()) {
// we may have no response if item failed
if (bulkItemResponse.getResponse() != null) {
bulkItemResponse.getResponse().setShardInfo(bulkShardResponse.getShardInfo());
}
responses.set(bulkItemResponse.getItemId(), bulkItemResponse);
}
if (counter.decrementAndGet() == 0) {
finishHim();
}
}
});
}
}
路由代码：
ShardId shardId = clusterService.operationRouting().indexShards(clusterState, concreteIndex, request.id(), request.routing()).shardId();