首页 > 代码库 > action support分析

action support分析

Action这一部分主要是数据(索引)的操作和部分集群信息操作。 所有的请求通过client转发到对应的action上然后再由对应的TransportAction来执行相关请求。如果请求能在本机上执行则在本机上执行,否则使用Transport进行转发到对应的节点。action support部分是对action的抽象,所有的具体action都继承了support action中的某个类。这里将对这些抽象类进行分析。

这一部分总共分为broadcast(广播),master,nodes,replication及single几个部分。broadcast主要针对一些无具体目标主机的操作,如查询index是否存在,所有继承这个类的action都具有这种类似的性质;nodes主要是对节点的操作,如热点线程查询(hotThread)查询节点上的繁忙线程;replication的子类主要是需要或可以在副本上进行的操作,如索引操作,数据不仅要发送到主shard还要发送到各个副本。single则主要是目标明确的单shard操作,如get操作,根据doc的id取doc,doc 的id能够确定它在哪个shard上,因此操作也在此shard上执行。

这些support action的实现可以分为两类,第一类就是实现一个内部类作为异步操作器,子类执行doExecute时,初始化该操作器并启动。另外一种就是直接实现一个方法,子类doExecute方法调用该方法进行。TransportBroadcastOperationAction就属于前者,它实现了内部操作器AsyncBroadcastAction。TransportCountAction继承于它,它doExecute方法如下所示:

 @Override
    protected void doExecute(CountRequest request, ActionListener<CountResponse> listener) {
        request.nowInMillis = System.currentTimeMillis();
        super.doExecute(request, listener);
    }

调用父类的doExecute方法,也就是TransportBroadcastOperationAction的方法,它的实现如下所示:

 @Override
    protected void doExecute(Request request, ActionListener<Response> listener) {
        new AsyncBroadcastAction(request, listener).start();
    }

可以看到它初始化了AsyncBroadcastAction并启动。AsyncBroadcastAction只是确定了操作的流程,及操作完成如何返回response,并未涉及到具体的操作逻辑。因为这些逻辑都在每个子action中实现,不同的action需要进行不同的操作。如count需要count每个shard并且返回最后的总数值,而IndexExistAction则需要对比所有索引查看查询的索引是否存在。start方法的代码如下所示:

public void start() {
      //没有shards
if (shardsIts.size() == 0) { // no shards try { listener.onResponse(newResponse(request, new AtomicReferenceArray(0), clusterState)); } catch (Throwable e) { listener.onFailure(e); } return; } request.beforeStart(); // count the local operations, and perform the non local ones int shardIndex = -1;
       //遍历对每个shards进行操作
for (final ShardIterator shardIt : shardsIts) { shardIndex++; final ShardRouting shard = shardIt.nextOrNull(); if (shard != null) { performOperation(shardIt, shard, shardIndex); } else { // really, no shards active in this group onOperation(null, shardIt, shardIndex, new NoShardAvailableActionException(shardIt.shardId())); } } }

start方法就是遍历所有shards,如果shard存在则执行performOperation方法,在这个方法中会区分该请求能否在本机上进行,能执行则调用shardOperation方法得到结果。这个方法在这是抽象的,每个子类都有实现。否则发送到对应的主机上。,如果shard为null则进行onOperation操作,遍历该shard的其它副本看能否找到可以操作的shard。performOperation代码如下所示:

 protected void performOperation(final ShardIterator shardIt, final ShardRouting shard, final int shardIndex) {
            if (shard == null) {//shard 为null抛出异常
                // no more active shards... (we should not really get here, just safety)
                onOperation(null, shardIt, shardIndex, new NoShardAvailableActionException(shardIt.shardId()));
            } else {
                try {
                    final ShardRequest shardRequest = newShardRequest(shardIt.size(), shard, request);
                    if (shard.currentNodeId().equals(nodes.localNodeId())) {//shard在本地执行shardOperation方法,并通过onOperation方法封装结果
                        threadPool.executor(executor).execute(new Runnable() {
                            @Override
                            public void run() {
                                try {
                                    onOperation(shard, shardIndex, shardOperation(shardRequest));
                                } catch (Throwable e) {
                                    onOperation(shard, shardIt, shardIndex, e);
                                }
                            }
                        });
                    } else {//不是本地shard,发送到对应节点。
                        DiscoveryNode node = nodes.get(shard.currentNodeId());
                        if (node == null) {
                            // no node connected, act as failure
                            onOperation(shard, shardIt, shardIndex, new NoShardAvailableActionException(shardIt.shardId()));
                        } else {
                            transportService.sendRequest(node, transportShardAction, shardRequest, new BaseTransportResponseHandler<ShardResponse>() {
                                @Override
                                public ShardResponse newInstance() {
                                    return newShardResponse();
                                }

                                @Override
                                public String executor() {
                                    return ThreadPool.Names.SAME;
                                }

                                @Override
                                public void handleResponse(ShardResponse response) {
                                    onOperation(shard, shardIndex, response);
                                }

                                @Override
                                public void handleException(TransportException e) {
                                    onOperation(shard, shardIt, shardIndex, e);
                                }
                            });
                        }
                    }
                } catch (Throwable e) {
                    onOperation(shard, shardIt, shardIndex, e);
                }
            }
        }

方法shardOperation在countTransportAction的实现如下所示:

    @Override
    protected ShardCountResponse shardOperation(ShardCountRequest request) throws ElasticsearchException {
        IndexService indexService = indicesService.indexServiceSafe(request.shardId().getIndex());//
        IndexShard indexShard = indexService.shardSafe(request.shardId().id());
    //构造查询context
        SearchShardTarget shardTarget = new SearchShardTarget(clusterService.localNode().id(), request.shardId().getIndex(), request.shardId().id());
        SearchContext context = new DefaultSearchContext(0,
                new ShardSearchLocalRequest(request.types(), request.nowInMillis(), request.filteringAliases()),
                shardTarget, indexShard.acquireSearcher("count"), indexService, indexShard,
                scriptService, cacheRecycler, pageCacheRecycler, bigArrays, threadPool.estimatedTimeInMillisCounter());
        SearchContext.setCurrent(context);

        try {
            // TODO: min score should move to be "null" as a value that is not initialized...
            if (request.minScore() != -1) {
                context.minimumScore(request.minScore());
            }
            BytesReference source = request.querySource();
            if (source != null && source.length() > 0) {
                try {
                    QueryParseContext.setTypes(request.types());
                    context.parsedQuery(indexService.queryParserService().parseQuery(source));
                } finally {
                    QueryParseContext.removeTypes();
                }
            }
            final boolean hasTerminateAfterCount = request.terminateAfter() != DEFAULT_TERMINATE_AFTER;
            boolean terminatedEarly = false;
            context.preProcess();
            try {
                long count;
                if (hasTerminateAfterCount) {//调用lucene的封装接口执行查询并返回结果
                    final Lucene.EarlyTerminatingCollector countCollector =
                            Lucene.createCountBasedEarlyTerminatingCollector(request.terminateAfter());
                    terminatedEarly = Lucene.countWithEarlyTermination(context.searcher(), context.query(), countCollector);
                    count = countCollector.count();
                } else {
                    count = Lucene.count(context.searcher(), context.query());
                }
                return new ShardCountResponse(request.shardId(), count, terminatedEarly);
            } catch (Exception e) {
                throw new QueryPhaseExecutionException(context, "failed to execute count", e);
            }
        } finally {
            // this will also release the index searcher
            context.close();
            SearchContext.removeCurrent();
        }
    }

可以看到这里是每个action真正的逻辑实现。因为这里涉及到index部分的内容,这里就不详细分析。后面关于index的分析会有涉及。这就是support action中的第一种实现。

第二种就master的相关操作,因此没有实现对应的操作类,而只是实现了一个方法。该方法的作用跟操作器作用相同,唯一的不同是它没有操作器这么多的变量, 而且它不是异步的。master的操作需要实时进行,执行过程中需要阻塞某些操作,保证集群状态一致性。这里就不再说明,请参考TransportMasterNodeOperationAction原码。

总结:本篇概括说了support action,并以countTransportAction为例说明了support Action中的异步操作器实现,最后简单的分析了master的同步操作。因为这里涉及到很多action不可能一一分析,有兴趣可以参考对应的代码。而且这里有以下index部分的内容,所以没有更深入的分析。在后面分析完index的相关功能后,会挑出几个重要的action做详细分析。

 

action support分析