Solr4.8.0源码分析(14) 之 SolrCloud索引深入(1)
上一章节《Solr In Action 笔记(4) 之 SolrCloud分布式索引基础》简要学习了SolrCloud的索引过程，本节开始将通过阅读源码来深入学习下SolrCloud的索引过程。
1. SolrCloud的索引过程流程图
这里借用下《solrCloud Update Request Handling 更新索引流程》流程图：
由上图可以看出，SolrCloud的索引过程主要通过一个索引链过程来实现的，那么本节主要讲述下索引链以及DistributedUpdateProcessor这个过程。
2. SolrCloud update索引链
- SolrCloud的Update索引链的类是UpdateRequestProcessorChain，这个类在Solr初始化的时候就会进行定义。
- SolrCloud的Update索引链的组成可以通过solrconfig.xml进行自定义，比较灵活，例如：
<updateRequestProcessorChain name="key" default="true">
<processor class="package.Class1" />
<processor class="package.Class2" >
<str name="someInitParam1">value</str>
<int name="someInitParam2">42</int>
</processor>
<processor class="solr.LogUpdateProcessorFactory" >
<int name="maxNumToLog">100</int>
</processor>
<processor class="solr.RunUpdateProcessorFactory" />
</updateRequestProcessorChain>
- 如果未自定义UpdateRequestProcessorChain，那么Solr就默认以下三个过程组成索引链，依次如下：
LogUpdateProcessorFactory， 它对应的处理过程为LogUpdateProcessor , 主要负责日志的记录；
DistributedUpdateProcessorFactory, 它对应的处理过程为DistributedUpdateProcessor ，主要负责对version的处理以及request的分发；
RunUpdateProcessorFactory, 它对应的处理过程为DirectUpdateHandler2 ，主要负责将记录add进本shard的lucene中；
- 如果最后一个索引链包含了RunUpdateProcessorFactory，但是没有包含DistributedUpdateProcessorFactory，那么Solr会在索引链init的时候自动在RunUpdateProcessorFactory前面加入DistributedUpdateProcessorFactory；
- 每一次update操作，都会重新创建一个索引链，即createProcessor，然后依次进行下去；
- update操作包含add，delete，commit，所以上述UpdateProcessor都会分别包含processAdd，processDelete，processCommit，依次可以细分成add 索引链，delete索引链，commit索引链。
明白了以上几点，那么开始学习索引链的源码
- 首先来查看索引链的init代码，UpdateRequestProcessorChain.init()在初始化SolrCore的时候就调用了
public void init(PluginInfo info) {
final String infomsg = "updateRequestProcessorChain \"" +
(null != info.name ? info.name : "") + "\"" +
(info.isDefault() ? " (default)" : "");
log.info("creating " + infomsg);
// wrap in an ArrayList so we know we know we can do fast index lookups
// and that add(int,Object) is supported
//从solrcore获取索引链的成员，存放成列表形式。索引链在Solrconfig.xml中是以插件的形式加入的
List<UpdateRequestProcessorFactory> list = new ArrayList
(solrCore.initPlugins(info.getChildren("processor"),UpdateRequestProcessorFactory.class,null));
if(list.isEmpty()){
throw new SolrException(SolrException.ErrorCode.SERVER_ERROR,
infomsg + " require at least one processor");
}
int numDistrib = 0;
int runIndex = -1;
// hi->lo incase multiple run instances, add before first one
// (no idea why someone might use multiple run instances, but just in case)
//从后往前遍历索引链列表，寻找DistributingUpdateProcessorFactory和RunUpdateProcessorFactory
for (int i = list.size()-1; 0 <= i; i--) {
UpdateRequestProcessorFactory factory = list.get(i);
if (factory instanceof DistributingUpdateProcessorFactory) {
numDistrib++; //DistributingUpdateProcessorFactory的个数不能超过1
}
if (factory instanceof RunUpdateProcessorFactory) {
runIndex = i; //RunUpdateProcessorFactory的编号
}
}
if (1 < numDistrib) {
throw new SolrException(SolrException.ErrorCode.SERVER_ERROR,
infomsg + " may not contain more then one " +
"instance of DistributingUpdateProcessorFactory");
}
//如果存在RunUpdateProcessorFactory且没有DistributingUpdateProcessorFactory，
//那么会在RunUpdateProcessorFactory之前加入DistributingUpdateProcessorFactory
if (0 <= runIndex && 0 == numDistrib) {
// by default, add distrib processor immediately before run
DistributedUpdateProcessorFactory distrib
= new DistributedUpdateProcessorFactory();
distrib.init(new NamedList());
list.add(runIndex, distrib);
log.info("inserting DistributedUpdateProcessorFactory into " + infomsg);
}
chain = list.toArray(new UpdateRequestProcessorFactory[list.size()]);
}
- 每当有update请求时候就会触发索引链的创建，UpdateRequestProcessorChain.createProcessor。
public UpdateRequestProcessor createProcessor(SolrQueryRequest req,
SolrQueryResponse rsp)
{
UpdateRequestProcessor processor = null;
UpdateRequestProcessor last = null;
//获取distribPhase 是否需要跳过DistributingUpdateProcessorFactory前面那一过程（即LogUpdateProcessor），该参数不是由客户端生成
final String distribPhase = req.getParams().get(DistributingUpdateProcessorFactory.DISTRIB_UPDATE_PARAM);
final boolean skipToDistrib = distribPhase != null;
boolean afterDistrib = true; // we iterate backwards, so true to start
//从后往前组件索引链即
//LogUpdateProcessor.next = DistributedUpdateProcessor
//DistributedUpdateProcessor.next = DirectUpdateHandler2
//DirectUpdateHandler2.next = null
for (int i = chain.length-1; i>=0; i--) {
UpdateRequestProcessorFactory factory = chain[i]; if (skipToDistrib) {
if (afterDistrib) {
// 跳过DistributingUpdateProcessorFactory前面的索引链过程
if (factory instanceof DistributingUpdateProcessorFactory) {
afterDistrib = false;
}
} else if (!(factory instanceof UpdateRequestProcessorFactory.RunAlways)) {
// skip anything that doesn't have the marker interface
continue;
}
}
//创建UpdateRequestProcessorFactory对应的UpdateProcessor，并进行连接
processor = factory.getInstance(req, rsp, last);
last = processor == null ? last : processor;
} return last;
}
- 在UpdateRequestProcessorChain.createProcessor会调用UpdateRequestProcessorFactory的getInstance创建对应的updateProcessor，
LogUpdateProcessor
public UpdateRequestProcessor getInstance(SolrQueryRequest req, SolrQueryResponse rsp, UpdateRequestProcessor next) {
return LogUpdateProcessor.log.isInfoEnabled() ? new LogUpdateProcessor(req, rsp, this, next) : null;
}
- DistributedUpdateProcessor
public DistributedUpdateProcessor getInstance(SolrQueryRequest req,
SolrQueryResponse rsp, UpdateRequestProcessor next) { return new DistributedUpdateProcessor(req, rsp, next);
}
RunUpdateProcessorFactory
public UpdateRequestProcessor getInstance(SolrQueryRequest req, SolrQueryResponse rsp, UpdateRequestProcessor next)
{
return new RunUpdateProcessor(req, next);
}
总结：本节主要学习了SolrCloud分布式索引的整体流程，以及SolrCloud建索引时候索引链的情况，下一节将详细介绍索引链的具体过程。