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深入浅出 jackrabbit 十 redolog 和 recovery.docx

 2009-09-17 00:00:00 来源:WEB开发网   
核心提示: Java代码privatevoidrun()throwsIOException{Listactions=redoLog.getActions();/*找到所有只有开始没有结束的事务,并将其加入到losers这个集合中*/for(Iteratorit=actions.iterator();it.h

Java代码   

private void run() throws IOException { 
    List actions = redoLog.getActions(); 
 
    /*找到所有只有开始没有结束的事务,并将其加入到losers这个集合中*/ 
    for (Iterator it = actions.iterator(); it.hasNext();) { 
      MultiIndex.Action a = (MultiIndex.Action) it.next(); 
      if (a.getType() == MultiIndex.Action.TYPE_START) { 
        losers.add(new Long(a.getTransactionId())); 
      } else if (a.getType() == MultiIndex.Action.TYPE_COMMIT) { 
        losers.remove(new Long(a.getTransactionId())); 
      } 
    } 
 
    /*找到最后一次成功提交的事务在redolog中的位置*/ 
    int lastSafeVolatileCommit = -1; 
    Set transactionIds = new HashSet(); 
    for (int i = 0; i < actions.size(); i++) { 
      MultiIndex.Action a = (MultiIndex.Action) actions.get(i); 
      if (a.getType() == MultiIndex.Action.TYPE_COMMIT) { 
        transactionIds.clear(); 
      } else if (a.getType() == MultiIndex.Action.TYPE_VOLATILE_COMMIT) { 
        transactionIds.retainAll(losers); 
        // check if transactionIds contains losers 
        if (transactionIds.size() > 0) { 
          // found dirty volatile commit 
          break; 
        } else { 
          lastSafeVolatileCommit = i; 
        } 
      } else { 
        transactionIds.add(new Long(a.getTransactionId())); 
      } 
    } 
 
    /*最后一次成功的事务之后的数据遍历一下,找到脏目录,脏目录是指在一次事务中创建的目录,但是事务最终没有被完整执行,那么这些目录应该被删除掉*/ 
    for (int i = lastSafeVolatileCommit + 1; i < actions.size(); i++) { 
      MultiIndex.Action a = (MultiIndex.Action) actions.get(i); 
      if (a.getType() == MultiIndex.Action.TYPE_CREATE_INDEX) { 
        a.undo(index); 
      } 
    } 
 
    /*将最后一次正确的事务之前的操作都重新做一遍*/ 
    for (int i = 0; i < actions.size() && i <= lastSafeVolatileCommit; i++) { 
      MultiIndex.Action a = (MultiIndex.Action) actions.get(i); 
      switch (a.getType()) { 
        case MultiIndex.Action.TYPE_ADD_INDEX: 
        case MultiIndex.Action.TYPE_CREATE_INDEX: 
        case MultiIndex.Action.TYPE_DELETE_INDEX: 
        case MultiIndex.Action.TYPE_DELETE_NODE: 
          // ignore actions by the index merger. 
          // the previously created index of a merge has been 
          // deleted because it was considered dirty. 
          // we are conservative here and let the index merger do 
          // its work again. 
          if (a.getTransactionId() == MultiIndex.Action.INTERNAL_TRANS_REPL_INDEXES) { 
            continue; 
          } 
          a.execute(index); 
      } 
    } 
 
    // now replay the rest until we encounter a loser transaction 
    for (int i = lastSafeVolatileCommit + 1; i < actions.size(); i++) { 
      MultiIndex.Action a = (MultiIndex.Action) actions.get(i); 
      if (losers.contains(new Long(a.getTransactionId()))) { 
        break; 
      } else { 
        // ignore actions by the index merger. 
        if (a.getTransactionId() == MultiIndex.Action.INTERNAL_TRANS_REPL_INDEXES) { 
          continue; 
        } 
        a.execute(index); 
      } 
    } 
 
    // now we are consistent again -> flush 
    index.flush(); 
    index.closeMultiReader(); 
  } 

从上面的这段代码可以看出,如果一个事务不完整,那么这个事务的操作将会全部回滚,而事务完整的操作将会被全部重做。

通过这些操作,redolog中的信息被解析出来,并执行,那么就可以找回丢失的数据,并且过滤掉错误的数据。

总结:redolog很重要。

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Tags:深入浅出 jackrabbit redolog

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