ES bulk源码分析——ES 5.0

Posted 2020-08-20 将者，智、信、仁、勇、严也。

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();