solr调用lucene底层实现倒排索引源码解析

1.什么是Lucene？

作为一个开放源代码项目，Lucene从问世之后，引发了开放源代码社群的巨大反响，程序员们不仅使用它构建具体的全文检索应用，而且将之集成到各种系统软件中去，以及构建Web应用，甚至某些商业软件也采用了Lucene作为其内部全文检索子系统的核心。apache软件基金会的网站使用了Lucene作为全文检索的引擎，IBM的开源软件eclipse的2.1版本中也采用了Lucene作为帮助子系统的全文索引引擎，相应的IBM的商业软件Web Sphere中也采用了Lucene。Lucene以其开放源代码的特性、优异的索引结构、良好的系统架构获得了越来越多的应用。

Lucene作为一个全文检索引擎，其具有如下突出的优点：

（1）索引文件格式独立于应用平台。Lucene定义了一套以8位字节为基础的索引文件格式，使得兼容系统或者不同平台的应用能够共享建立的索引文件。

（2）在传统全文检索引擎的倒排索引的基础上，实现了分块索引，能够针对新的文件建立小文件索引，提升索引速度。然后通过与原有索引的合并，达到优化的目的。

（3）优秀的面向对象的系统架构，使得对于Lucene扩展的学习难度降低，方便扩充新功能。

（4）设计了独立于语言和文件格式的文本分析接口，索引器通过接受Token流完成索引文件的创立，用户扩展新的语言和文件格式，只需要实现文本分析的接口。

（5）已经默认实现了一套强大的查询引擎，用户无需自己编写代码即使系统可获得强大的查询能力，Lucene的查询实现中默认实现了布尔操作、模糊查询（Fuzzy Search）、分组查询等等。

2.什么是solr？

为什么要solr：

1、solr是将整个索引操作功能封装好了的搜索引擎系统(企业级搜索引擎产品)

2、solr可以部署到单独的服务器上(WEB服务)，它可以提供服务，我们的业务系统就只要发送请求，接收响应即可，降低了业务系统的负载

3、solr部署在专门的服务器上，它的索引库就不会受业务系统服务器存储空间的限制

4、solr支持分布式集群，索引服务的容量和能力可以线性扩展

solr的工作机制：

1、solr就是在lucene工具包的基础之上进行了封装，而且是以web服务的形式对外提供索引功能

2、业务系统需要使用到索引的功能（建索引，查索引）时，只要发出http请求，并将返回数据进行解析即可

Solr 是Apache下的一个顶级开源项目，采用Java开发，它是基于Lucene的全文搜索服务器。Solr提供了比Lucene更为丰富的查询语言，同时实现了可配置、可扩展，并对索引、搜索性能进行了优化。

Solr可以独立运行，运行在Jetty、Tomcat等这些Servlet容器中，Solr 索引的实现方法很简单，用 POST 方法向 Solr 服务器发送一个描述 Field 及其内容的 XML 文档，Solr根据xml文档添加、删除、更新索引 。Solr 搜索只需要发送 HTTP GET 请求，然后对 Solr 返回Xml、json等格式的查询结果进行解析，组织页面布局。Solr不提供构建UI的功能，Solr提供了一个管理界面，通过管理界面可以查询Solr的配置和运行情况。

3.lucene和solr的关系

solr是门户，lucene是底层基础，solr和lucene的关系正如hadoop和hdfs的关系。那么solr是怎么调用到lucene的呢？

我们以查询为例，来看一下整个过程，导入过程可以参考:

solr源码分析之数据导入DataImporter追溯

4.solr是怎么调用到lucene？

4.1.准备工作

lucene-solr本地调试方法

使用内置jetty启动main方法。

4.2 进入Solr-admin：http://localhost:8983/solr/

创建一个new_core集合

4.3 进入http://localhost:8983/solr/#/new_core/query

选择一个field进行查询

4.4 入口是SolrDispatchFilter，整个流程如流程图所示

从上面的流程图可以看出，solr采用filter的模式(如struts2,springmvc使用servlet模式)，然后以容器的方式来封装各种Handler，Handler负责处理各种请求，最终调用的是lucene的底层实现。

注意：solr没有使用lucene本身的QueryParser，而是自己重写了这个组件。

4.4.1 SolrDispatchFilter入口

 public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain, boolean retry) throws IOException, ServletException {
    if (!(request instanceof HttpServletRequest)) return;

    try {

      if (cores == null || cores.isShutDown()) {
        try {
          init.await();
        } catch (InterruptedException e) { //well, no wait then
        }
        final String msg = "Error processing the request. CoreContainer is either not initialized or shutting down.";
        if (cores == null || cores.isShutDown()) {
          log.error(msg);
          throw new UnavailableException(msg);
        }
      }

      AtomicReference<ServletRequest> wrappedRequest = new AtomicReference<>();
      if (!authenticateRequest(request, response, wrappedRequest)) { // the response and status code have already been
                                                                     // sent
        return;
      }
      if (wrappedRequest.get() != null) {
        request = wrappedRequest.get();
      }

      request = closeShield(request, retry);
      response = closeShield(response, retry);

      if (cores.getAuthenticationPlugin() != null) {
        log.debug("User principal: {}", ((HttpServletRequest) request).getUserPrincipal());
      }

      // No need to even create the HttpSolrCall object if this path is excluded.
      if (excludePatterns != null) {
        String requestPath = ((HttpServletRequest) request).getServletPath();
        String extraPath = ((HttpServletRequest) request).getPathInfo();
        if (extraPath != null) { // In embedded mode, servlet path is empty - include all post-context path here for
                                 // testing
          requestPath += extraPath;
        }
        for (Pattern p : excludePatterns) {
          Matcher matcher = p.matcher(requestPath);
          if (matcher.lookingAt()) {
            chain.doFilter(request, response);
            return;
          }
        }
      }

      HttpSolrCall call = getHttpSolrCall((HttpServletRequest) request, (HttpServletResponse) response, retry);
      ExecutorUtil.setServerThreadFlag(Boolean.TRUE);
      try {
        Action result = call.call(); //1
        switch (result) {
          case PASSTHROUGH:
            chain.doFilter(request, response);
            break;
          case RETRY:
            doFilter(request, response, chain, true);
            break;
          case FORWARD:
            request.getRequestDispatcher(call.getPath()).forward(request, response);
            break;
        }
      } finally {
        call.destroy();
        ExecutorUtil.setServerThreadFlag(null);
      }
    } finally {
      consumeInputFully((HttpServletRequest) request);
    }
  }

红色部分的调用

4.4.2 HttpSolrCall

 /**
   * This method processes the request.
   */
  public Action call() throws IOException {
    MDCLoggingContext.reset();
    MDCLoggingContext.setNode(cores);

    if (cores == null) {
      sendError(503, "Server is shutting down or failed to initialize");
      return RETURN;
    }

    if (solrDispatchFilter.abortErrorMessage != null) {
      sendError(500, solrDispatchFilter.abortErrorMessage);
      return RETURN;
    }

    try {
      init();//1
      /* Authorize the request if
       1. Authorization is enabled, and
       2. The requested resource is not a known static file
        */
      if (cores.getAuthorizationPlugin() != null && shouldAuthorize()) {
        AuthorizationContext context = getAuthCtx();
        log.debug("AuthorizationContext : {}", context);
        AuthorizationResponse authResponse = cores.getAuthorizationPlugin().authorize(context);
        if (authResponse.statusCode == AuthorizationResponse.PROMPT.statusCode) {
          Map<String, String> headers = (Map) getReq().getAttribute(AuthenticationPlugin.class.getName());
          if (headers != null) {
            for (Map.Entry<String, String> e : headers.entrySet()) response.setHeader(e.getKey(), e.getValue());
          }
          log.debug("USER_REQUIRED "+req.getHeader("Authorization")+" "+ req.getUserPrincipal());
        }
        if (!(authResponse.statusCode == HttpStatus.SC_ACCEPTED) && !(authResponse.statusCode == HttpStatus.SC_OK)) {
          log.info("USER_REQUIRED auth header {} context : {} ", req.getHeader("Authorization"), context);
          sendError(authResponse.statusCode,
              "Unauthorized request, Response code: " + authResponse.statusCode);
          return RETURN;
        }
      }

      HttpServletResponse resp = response;
      switch (action) {
        case ADMIN:
          handleAdminRequest();
          return RETURN;
        case REMOTEQUERY:
          remoteQuery(coreUrl + path, resp);
          return RETURN;
        case PROCESS:
          final Method reqMethod = Method.getMethod(req.getMethod());
          HttpCacheHeaderUtil.setCacheControlHeader(config, resp, reqMethod);
          // unless we have been explicitly told not to, do cache validation
          // if we fail cache validation, execute the query
          if (config.getHttpCachingConfig().isNever304() ||
              !HttpCacheHeaderUtil.doCacheHeaderValidation(solrReq, req, reqMethod, resp)) {
            SolrQueryResponse solrRsp = new SolrQueryResponse();
              /* even for HEAD requests, we need to execute the handler to
               * ensure we don't get an error (and to make sure the correct
               * QueryResponseWriter is selected and we get the correct
               * Content-Type)
               */
            SolrRequestInfo.setRequestInfo(new SolrRequestInfo(solrReq, solrRsp));
            execute(solrRsp); //2
            HttpCacheHeaderUtil.checkHttpCachingVeto(solrRsp, resp, reqMethod);
            Iterator<Map.Entry<String, String>> headers = solrRsp.httpHeaders();
            while (headers.hasNext()) {
              Map.Entry<String, String> entry = headers.next();
              resp.addHeader(entry.getKey(), entry.getValue());
            }
            QueryResponseWriter responseWriter = getResponseWriter();
            if (invalidStates != null) solrReq.getContext().put(CloudSolrClient.STATE_VERSION, invalidStates);
            writeResponse(solrRsp, responseWriter, reqMethod);
          }
          return RETURN;
        default: return action;
      }
    } catch (Throwable ex) {
      sendError(ex);
      // walk the the entire cause chain to search for an Error
      Throwable t = ex;
      while (t != null) {
        if (t instanceof Error) {
          if (t != ex) {
            log.error("An Error was wrapped in another exception - please report complete stacktrace on SOLR-6161", ex);
          }
          throw (Error) t;
        }
        t = t.getCause();
      }
      return RETURN;
    } finally {
      MDCLoggingContext.clear();
    }

  }

其中 1初始化，2.执行请求调用

4.4.3 获取Handler

protected void init() throws Exception {
    // check for management path
    String alternate = cores.getManagementPath();
    if (alternate != null && path.startsWith(alternate)) {
      path = path.substring(0, alternate.length());
    }

    // unused feature ?
    int idx = path.indexOf(':');
    if (idx > 0) {
      // save the portion after the ':' for a 'handler' path parameter
      path = path.substring(0, idx);
    }

    // Check for container handlers
    handler = cores.getRequestHandler(path);
    if (handler != null) {
      solrReq = SolrRequestParsers.DEFAULT.parse(null, path, req);
      solrReq.getContext().put(CoreContainer.class.getName(), cores);
      requestType = RequestType.ADMIN;
      action = ADMIN;
      return;
    }

    // Parse a core or collection name from the path and attempt to see if it's a core name
    idx = path.indexOf("/", 1);
    if (idx > 1) {
      origCorename = path.substring(1, idx);

      // Try to resolve a Solr core name
      core = cores.getCore(origCorename);
      if (core != null) {
        path = path.substring(idx);
      } else {
        if (cores.isCoreLoading(origCorename)) { // extra mem barriers, so don't look at this before trying to get core
          throw new SolrException(ErrorCode.SERVICE_UNAVAILABLE, "SolrCore is loading");
        }
        // the core may have just finished loading
        core = cores.getCore(origCorename);
        if (core != null) {
          path = path.substring(idx);
        } else {
          if (!cores.isZooKeeperAware()) {
            core = cores.getCore("");
          }
        }
      }
    }

    if (cores.isZooKeeperAware()) {
      // init collectionList (usually one name but not when there are aliases)
      String def = core != null ? core.getCoreDescriptor().getCollectionName() : origCorename;
      collectionsList = resolveCollectionListOrAlias(queryParams.get(COLLECTION_PROP, def)); // &collection= takes precedence

      if (core == null) {
        // lookup core from collection, or route away if need to
        String collectionName = collectionsList.isEmpty() ? null : collectionsList.get(0); // route to 1st
        //TODO try the other collections if can't find a local replica of the first?   (and do to V2HttpSolrCall)

        boolean isPreferLeader = (path.endsWith("/update") || path.contains("/update/"));

        core = getCoreByCollection(collectionName, isPreferLeader); // find a local replica/core for the collection
        if (core != null) {
          if (idx > 0) {
            path = path.substring(idx);
          }
        } else {
          // if we couldn't find it locally, look on other nodes
          if (idx > 0) {
            extractRemotePath(collectionName, origCorename);
            if (action == REMOTEQUERY) {
              path = path.substring(idx);
              return;
            }
          }
          //core is not available locally or remotely
          autoCreateSystemColl(collectionName);
          if (action != null) return;
        }
      }
    }

    // With a valid core...
    if (core != null) {
      MDCLoggingContext.setCore(core);
      config = core.getSolrConfig();
      // get or create/cache the parser for the core
      SolrRequestParsers parser = config.getRequestParsers();

      // Determine the handler from the url path if not set
      // (we might already have selected the cores handler)
      extractHandlerFromURLPath(parser);
      if (action != null) return;

      // With a valid handler and a valid core...
      if (handler != null) {
        // if not a /select, create the request
        if (solrReq == null) {
          solrReq = parser.parse(core, path, req);
        }

        invalidStates = checkStateVersionsAreValid(solrReq.getParams().get(CloudSolrClient.STATE_VERSION));

        addCollectionParamIfNeeded(getCollectionsList());

        action = PROCESS;
        return; // we are done with a valid handler
      }
    }
    log.debug("no handler or core retrieved for " + path + ", follow through...");

    action = PASSTHROUGH;
  }

4.4.4 CoreContainer

  public SolrRequestHandler getRequestHandler(String path) {
    return RequestHandlerBase.getRequestHandler(path, containerHandlers);
  }

4.4.5 RequestHandlerBase

  /**
   * Get the request handler registered to a given name.
   *
   * This function is thread safe.
   */
  public static SolrRequestHandler getRequestHandler(String handlerName, PluginBag<SolrRequestHandler> reqHandlers) {
    if(handlerName == null) return null;
    SolrRequestHandler handler = reqHandlers.get(handlerName);
    int idx = 0;
    if(handler == null) {
      for (; ; ) {
        idx = handlerName.indexOf('/', idx+1);
        if (idx > 0) {
          String firstPart = handlerName.substring(0, idx);
          handler = reqHandlers.get(firstPart);
          if (handler == null) continue;
          if (handler instanceof NestedRequestHandler) {
            return ((NestedRequestHandler) handler).getSubHandler(handlerName.substring(idx));
          }
        } else {
          break;
        }
      }
    }
    return handler;
  }

4.4.6HttpSolrCall

  protected void execute(SolrQueryResponse rsp) {
    // a custom filter could add more stuff to the request before passing it on.
    // for example: sreq.getContext().put( "HttpServletRequest", req );
    // used for logging query stats in SolrCore.execute()
    solrReq.getContext().put("webapp", req.getContextPath());
    solrReq.getCore().execute(handler, solrReq, rsp);
  }

4.4.7 SolrCore

  public void execute(SolrRequestHandler handler, SolrQueryRequest req, SolrQueryResponse rsp) {
    if (handler==null) {
      String msg = "Null Request Handler '" +
        req.getParams().get(CommonParams.QT) + "'";

      if (log.isWarnEnabled()) log.warn(logid + msg + ":" + req);

      throw new SolrException(ErrorCode.BAD_REQUEST, msg);
    }

    preDecorateResponse(req, rsp);

    if (requestLog.isDebugEnabled() && rsp.getToLog().size() > 0) {
      // log request at debug in case something goes wrong and we aren't able to log later
      requestLog.debug(rsp.getToLogAsString(logid));
    }

    // TODO: this doesn't seem to be working correctly and causes problems with the example server and distrib (for example /spell)
    // if (req.getParams().getBool(ShardParams.IS_SHARD,false) && !(handler instanceof SearchHandler))
    //   throw new SolrException(SolrException.ErrorCode.BAD_REQUEST,"isShard is only acceptable with search handlers");

    handler.handleRequest(req,rsp);
    postDecorateResponse(handler, req, rsp);

    if (rsp.getToLog().size() > 0) {
      if (requestLog.isInfoEnabled()) {
        requestLog.info(rsp.getToLogAsString(logid));
      }

      if (log.isWarnEnabled() && slowQueryThresholdMillis >= 0) {
        final long qtime = (long) (req.getRequestTimer().getTime());
        if (qtime >= slowQueryThresholdMillis) {
          log.warn("slow: " + rsp.getToLogAsString(logid));
        }
      }
    }
  }

4.4.8 RequestHandlerBase

@Override
  public void handleRequest(SolrQueryRequest req, SolrQueryResponse rsp) {
    requests.inc();
    Timer.Context timer = requestTimes.time();
    try {
      if(pluginInfo != null && pluginInfo.attributes.containsKey(USEPARAM)) req.getContext().put(USEPARAM,pluginInfo.attributes.get(USEPARAM));
      SolrPluginUtils.setDefaults(this, req, defaults, appends, invariants);
      req.getContext().remove(USEPARAM);
      rsp.setHttpCaching(httpCaching);
      handleRequestBody( req, rsp );
      // count timeouts
      NamedList header = rsp.getResponseHeader();
      if(header != null) {
        Object partialResults = header.get(SolrQueryResponse.RESPONSE_HEADER_PARTIAL_RESULTS_KEY);
        boolean timedOut = partialResults == null ? false : (Boolean)partialResults;
        if( timedOut ) {
          numTimeouts.mark();
          rsp.setHttpCaching(false);
        }
      }
    } catch (Exception e) {
      boolean incrementErrors = true;
      boolean isServerError = true;
      if (e instanceof SolrException) {
        SolrException se = (SolrException)e;
        if (se.code() == SolrException.ErrorCode.CONFLICT.code) {
          incrementErrors = false;
        } else if (se.code() >= 400 && se.code() < 500) {
          isServerError = false;
        }
      } else {
        if (e instanceof SyntaxError) {
          isServerError = false;
          e = new SolrException(SolrException.ErrorCode.BAD_REQUEST, e);
        }
      }

      rsp.setException(e);

      if (incrementErrors) {
        SolrException.log(log, e);

        numErrors.mark();
        if (isServerError) {
          numServerErrors.mark();
        } else {
          numClientErrors.mark();
        }
      }
    } finally {
      long elapsed = timer.stop();
      totalTime.inc(elapsed);
    }
  }

4.4.9 SearchHandler

@Override
  public void handleRequestBody(SolrQueryRequest req, SolrQueryResponse rsp) throws Exception
  {
    List<SearchComponent> components  = getComponents();
    ResponseBuilder rb = new ResponseBuilder(req, rsp, components);
    if (rb.requestInfo != null) {
      rb.requestInfo.setResponseBuilder(rb);
    }

    boolean dbg = req.getParams().getBool(CommonParams.DEBUG_QUERY, false);
    rb.setDebug(dbg);
    if (dbg == false){//if it's true, we are doing everything anyway.
      SolrPluginUtils.getDebugInterests(req.getParams().getParams(CommonParams.DEBUG), rb);
    }

    final RTimerTree timer = rb.isDebug() ? req.getRequestTimer() : null;

    final ShardHandler shardHandler1 = getAndPrepShardHandler(req, rb); // creates a ShardHandler object only if it's needed

    if (timer == null) {
      // non-debugging prepare phase
      for( SearchComponent c : components ) {
        c.prepare(rb);  //1
      }
    } else {
      // debugging prepare phase
      RTimerTree subt = timer.sub( "prepare" );
      for( SearchComponent c : components ) {
        rb.setTimer( subt.sub( c.getName() ) );
        c.prepare(rb);
        rb.getTimer().stop();
      }
      subt.stop();
    }

    if (!rb.isDistrib) {
      // a normal non-distributed request

      long timeAllowed = req.getParams().getLong(CommonParams.TIME_ALLOWED, -1L);
      if (timeAllowed > 0L) {
        SolrQueryTimeoutImpl.set(timeAllowed);
      }
      try {
        // The semantics of debugging vs not debugging are different enough that
        // it makes sense to have two control loops
        if(!rb.isDebug()) {
          // Process
          for( SearchComponent c : components ) {
            c.process(rb); //2
          }
        }
        else {
          // Process
          RTimerTree subt = timer.sub( "process" );
          for( SearchComponent c : components ) {
            rb.setTimer( subt.sub( c.getName() ) );
            c.process(rb);
            rb.getTimer().stop();
          }
          subt.stop();

          // add the timing info
          if (rb.isDebugTimings()) {
            rb.addDebugInfo("timing", timer.asNamedList() );
          }
        }
      } catch (ExitableDirectoryReader.ExitingReaderException ex) {
        log.warn( "Query: " + req.getParamString() + "; " + ex.getMessage());
        SolrDocumentList r = (SolrDocumentList) rb.rsp.getResponse();
        if(r == null)
          r = new SolrDocumentList();
        r.setNumFound(0);
        rb.rsp.addResponse(r);
        if(rb.isDebug()) {
          NamedList debug = new NamedList();
          debug.add("explain", new NamedList());
          rb.rsp.add("debug", debug);
        }
        rb.rsp.getResponseHeader().add(SolrQueryResponse.RESPONSE_HEADER_PARTIAL_RESULTS_KEY, Boolean.TRUE);
      } finally {
        SolrQueryTimeoutImpl.reset();
      }
    } else {
      // a distributed request

      if (rb.outgoing == null) {
        rb.outgoing = new LinkedList<>();
      }
      rb.finished = new ArrayList<>();

      int nextStage = 0;
      do {
        rb.stage = nextStage;
        nextStage = ResponseBuilder.STAGE_DONE;

        // call all components
        for( SearchComponent c : components ) {
          // the next stage is the minimum of what all components report
          nextStage = Math.min(nextStage, c.distributedProcess(rb));
        }

        // check the outgoing queue and send requests
        while (rb.outgoing.size() > 0) {

          // submit all current request tasks at once
          while (rb.outgoing.size() > 0) {
            ShardRequest sreq = rb.outgoing.remove(0);
            sreq.actualShards = sreq.shards;
            if (sreq.actualShards==ShardRequest.ALL_SHARDS) {
              sreq.actualShards = rb.shards;
            }
            sreq.responses = new ArrayList<>(sreq.actualShards.length); // presume we'll get a response from each shard we send to

            // TODO: map from shard to address[]
            for (String shard : sreq.actualShards) {
              ModifiableSolrParams params = new ModifiableSolrParams(sreq.params);
              params.remove(ShardParams.SHARDS);      // not a top-level request
              params.set(DISTRIB, "false");               // not a top-level request
              params.remove("indent");
              params.remove(CommonParams.HEADER_ECHO_PARAMS);
              params.set(ShardParams.IS_SHARD, true);  // a sub (shard) request
              params.set(ShardParams.SHARDS_PURPOSE, sreq.purpose);
              params.set(ShardParams.SHARD_URL, shard); // so the shard knows what was asked
              if (rb.requestInfo != null) {
                // we could try and detect when this is needed, but it could be tricky
                params.set("NOW", Long.toString(rb.requestInfo.getNOW().getTime()));
              }
              String shardQt = params.get(ShardParams.SHARDS_QT);
              if (shardQt != null) {
                params.set(CommonParams.QT, shardQt);
              } else {
                // for distributed queries that don't include shards.qt, use the original path
                // as the default but operators need to update their luceneMatchVersion to enable
                // this behavior since it did not work this way prior to 5.1
                String reqPath = (String) req.getContext().get(PATH);
                if (!"/select".equals(reqPath)) {
                  params.set(CommonParams.QT, reqPath);
                } // else if path is /select, then the qt gets passed thru if set
              }
              shardHandler1.submit(sreq, shard, params);
            }
          }

          // now wait for replies, but if anyone puts more requests on
          // the outgoing queue, send them out immediately (by exiting
          // this loop)
          boolean tolerant = rb.req.getParams().getBool(ShardParams.SHARDS_TOLERANT, false);
          while (rb.outgoing.size() == 0) {
            ShardResponse srsp = tolerant ?
                shardHandler1.takeCompletedIncludingErrors():
                shardHandler1.takeCompletedOrError();
            if (srsp == null) break;  // no more requests to wait for

            // Was there an exception?
            if (srsp.getException() != null) {
              // If things are not tolerant, abort everything and rethrow
              if(!tolerant) {
                shardHandler1.cancelAll();
                if (srsp.getException() instanceof SolrException) {
                  throw (SolrException)srsp.getException();
                } else {
                  throw new SolrException(SolrException.ErrorCode.SERVER_ERROR, srsp.getException());
                }
              } else {
                if(rsp.getResponseHeader().get(SolrQueryResponse.RESPONSE_HEADER_PARTIAL_RESULTS_KEY) == null) {
                  rsp.getResponseHeader().add(SolrQueryResponse.RESPONSE_HEADER_PARTIAL_RESULTS_KEY, Boolean.TRUE);
                }
              }
            }

            rb.finished.add(srsp.getShardRequest());

            // let the components see the responses to the request
            for(SearchComponent c : components) {
              c.handleResponses(rb, srsp.getShardRequest());
            }
          }
        }

        for(SearchComponent c : components) {
          c.finishStage(rb);
        }  //3

        // we are done when the next stage is MAX_VALUE
      } while (nextStage != Integer.MAX_VALUE);
    }

    // SOLR-5550: still provide shards.info if requested even for a short circuited distrib request
    if(!rb.isDistrib && req.getParams().getBool(ShardParams.SHARDS_INFO, false) && rb.shortCircuitedURL != null) {
      NamedList<Object> shardInfo = new SimpleOrderedMap<Object>();
      SimpleOrderedMap<Object> nl = new SimpleOrderedMap<Object>();
      if (rsp.getException() != null) {
        Throwable cause = rsp.getException();
        if (cause instanceof SolrServerException) {
          cause = ((SolrServerException)cause).getRootCause();
        } else {
          if (cause.getCause() != null) {
            cause = cause.getCause();
          }
        }
        nl.add("error", cause.toString() );
        StringWriter trace = new StringWriter();
        cause.printStackTrace(new PrintWriter(trace));
        nl.add("trace", trace.toString() );
      }
      else {
        nl.add("numFound", rb.getResults().docList.matches());
        nl.add("maxScore", rb.getResults().docList.maxScore());
      }
      nl.add("shardAddress", rb.shortCircuitedURL);
      nl.add("time", req.getRequestTimer().getTime()); // elapsed time of this request so far

      int pos = rb.shortCircuitedURL.indexOf("://");
      String shardInfoName = pos != -1 ? rb.shortCircuitedURL.substring(pos+3) : rb.shortCircuitedURL;
      shardInfo.add(shardInfoName, nl);
      rsp.getValues().add(ShardParams.SHARDS_INFO,shardInfo);
    }
  }

4.4.10 QueryComponent

 /**
   * Actually run the query
   */
  @Override
  public void process(ResponseBuilder rb) throws IOException
  {
    LOG.debug("process: {}", rb.req.getParams());

    SolrQueryRequest req = rb.req;
    SolrParams params = req.getParams();
    if (!params.getBool(COMPONENT_NAME, true)) {
      return;
    }

    StatsCache statsCache = req.getCore().getStatsCache();

    int purpose = params.getInt(ShardParams.SHARDS_PURPOSE, ShardRequest.PURPOSE_GET_TOP_IDS);
    if ((purpose & ShardRequest.PURPOSE_GET_TERM_STATS) != 0) {
      SolrIndexSearcher searcher = req.getSearcher();
      statsCache.returnLocalStats(rb, searcher);
      return;
    }
    // check if we need to update the local copy of global dfs
    if ((purpose & ShardRequest.PURPOSE_SET_TERM_STATS) != 0) {
      // retrieve from request and update local cache
      statsCache.receiveGlobalStats(req);
    }

    // Optional: This could also be implemented by the top-level searcher sending
    // a filter that lists the ids... that would be transparent to
    // the request handler, but would be more expensive (and would preserve score
    // too if desired).
    if (doProcessSearchByIds(rb)) {
      return;
    }

    // -1 as flag if not set.
    long timeAllowed = params.getLong(CommonParams.TIME_ALLOWED, -1L);
    if (null != rb.getCursorMark() && 0 < timeAllowed) {
      // fundamentally incompatible
      throw new SolrException(SolrException.ErrorCode.BAD_REQUEST, "Can not search using both " +
                              CursorMarkParams.CURSOR_MARK_PARAM + " and " + CommonParams.TIME_ALLOWED);
    }

    QueryCommand cmd = rb.getQueryCommand();
    cmd.setTimeAllowed(timeAllowed);

    req.getContext().put(SolrIndexSearcher.STATS_SOURCE, statsCache.get(req));

    QueryResult result = new QueryResult();

    cmd.setSegmentTerminateEarly(params.getBool(CommonParams.SEGMENT_TERMINATE_EARLY, CommonParams.SEGMENT_TERMINATE_EARLY_DEFAULT));
    if (cmd.getSegmentTerminateEarly()) {
      result.setSegmentTerminatedEarly(Boolean.FALSE);
    }

    //
    // grouping / field collapsing
    //
    GroupingSpecification groupingSpec = rb.getGroupingSpec();
    if (groupingSpec != null) {
      cmd.setSegmentTerminateEarly(false); // not supported, silently ignore any segmentTerminateEarly flag
      try {
        if (params.getBool(GroupParams.GROUP_DISTRIBUTED_FIRST, false)) {
          doProcessGroupedDistributedSearchFirstPhase(rb, cmd, result);
          return;
        } else if (params.getBool(GroupParams.GROUP_DISTRIBUTED_SECOND, false)) {
          doProcessGroupedDistributedSearchSecondPhase(rb, cmd, result);
          return;
        }

        doProcessGroupedSearch(rb, cmd, result);
        return;
      } catch (SyntaxError e) {
        throw new SolrException(SolrException.ErrorCode.BAD_REQUEST, e);
      }
    }

    // normal search result
    doProcessUngroupedSearch(rb, cmd, result);
  }

4.4.11 SolrIndexSearcher

  private void doProcessUngroupedSearch(ResponseBuilder rb, QueryCommand cmd, QueryResult result) throws IOException {

    SolrQueryRequest req = rb.req;
    SolrQueryResponse rsp = rb.rsp;

    SolrIndexSearcher searcher = req.getSearcher();

    searcher.search(result, cmd);
    rb.setResult(result);

    ResultContext ctx = new BasicResultContext(rb);
    rsp.addResponse(ctx);
    rsp.getToLog().add("hits", rb.getResults().docList.matches());

    if ( ! rb.req.getParams().getBool(ShardParams.IS_SHARD,false) ) {
      if (null != rb.getNextCursorMark()) {
        rb.rsp.add(CursorMarkParams.CURSOR_MARK_NEXT,
                   rb.getNextCursorMark().getSerializedTotem());
      }
    }

    if(rb.mergeFieldHandler != null) {
      rb.mergeFieldHandler.handleMergeFields(rb, searcher);
    } else {
      doFieldSortValues(rb, searcher);
    }

    doPrefetch(rb);
  }

4.4.12SolrIndexSearcher

/**
   * Builds the necessary collector chain (via delegate wrapping) and executes the query against it. This method takes
   * into consideration both the explicitly provided collector and postFilter as well as any needed collector wrappers
   * for dealing with options specified in the QueryCommand.
   */
  private void buildAndRunCollectorChain(QueryResult qr, Query query, Collector collector, QueryCommand cmd,
      DelegatingCollector postFilter) throws IOException {

    EarlyTerminatingSortingCollector earlyTerminatingSortingCollector = null;
    if (cmd.getSegmentTerminateEarly()) {
      final Sort cmdSort = cmd.getSort();
      final int cmdLen = cmd.getLen();
      final Sort mergeSort = core.getSolrCoreState().getMergePolicySort();

      if (cmdSort == null || cmdLen <= 0 || mergeSort == null ||
          !EarlyTerminatingSortingCollector.canEarlyTerminate(cmdSort, mergeSort)) {
        log.warn("unsupported combination: segmentTerminateEarly=true cmdSort={} cmdLen={} mergeSort={}", cmdSort, cmdLen, mergeSort);
      } else {
        collector = earlyTerminatingSortingCollector = new EarlyTerminatingSortingCollector(collector, cmdSort, cmd.getLen());
      }
    }

    final boolean terminateEarly = cmd.getTerminateEarly();
    if (terminateEarly) {
      collector = new EarlyTerminatingCollector(collector, cmd.getLen());
    }

    final long timeAllowed = cmd.getTimeAllowed();
    if (timeAllowed > 0) {
      collector = new TimeLimitingCollector(collector, TimeLimitingCollector.getGlobalCounter(), timeAllowed);
    }

    if (postFilter != null) {
      postFilter.setLastDelegate(collector);
      collector = postFilter;
    }

    try {
      super.search(query, collector);
    } catch (TimeLimitingCollector.TimeExceededException | ExitableDirectoryReader.ExitingReaderException x) {
      log.warn("Query: [{}]; {}", query, x.getMessage());
      qr.setPartialResults(true);
    } catch (EarlyTerminatingCollectorException etce) {
      if (collector instanceof DelegatingCollector) {
        ((DelegatingCollector) collector).finish();
      }
      throw etce;
    } finally {
      if (earlyTerminatingSortingCollector != null) {
        qr.setSegmentTerminatedEarly(earlyTerminatingSortingCollector.terminatedEarly());
      }
    }
    if (collector instanceof DelegatingCollector) {
      ((DelegatingCollector) collector).finish();
    }
  }

5.总结

从solr-lucene架构图所示，solr封装了handler来处理各种请求，底下是SearchComponent，分为pre，process，post三阶段处理，最后调用lucene的底层api。

lucene 底层通过Similarity来完成打分过程，详细 介绍了lucene的底层文件结构，和一步步如何实现打分。

参考资料：

【1】http://www.blogjava.net/hoojo/archive/2012/09/06/387140.html

【2】https://www.cnblogs.com/peaceliu/p/7786851.html