Hive metastore源码阅读（二）

　　最近随着项目的深入，发现hive meta有些弊端，就是你会发现它的元数据操作与操作物理集群的代码耦合在一起，非常不利于扩展。比如：在create_table的时候同时进行路径校验及创建，如下代码：

   if (!TableType.VIRTUAL_VIEW.toString().equals(tbl.getTableType())) {
           if (tbl.getSd().getLocation() == null
               || tbl.getSd().getLocation().isEmpty()) {
             tblPath = wh.getTablePath(
                 ms.getDatabase(tbl.getDbName()), tbl.getTableName());
           } else {
             if (!isExternal(tbl) && !MetaStoreUtils.isNonNativeTable(tbl)) {
               LOG.warn("Location: " + tbl.getSd().getLocation()
                   + " specified for non-external table:" + tbl.getTableName());
             }
             tblPath = wh.getDnsPath(new Path(tbl.getSd().getLocation()));
           }
           tbl.getSd().setLocation(tblPath.toString());
         }

         if (tblPath != null) {
           if (!wh.isDir(tblPath)) {
             if (!wh.mkdirs(tblPath, true)) {
               throw new MetaException(tblPath
                   + " is not a directory or unable to create one");
             }
             madeDir = true;
           }

　　　所以这是meta无法统一所有元数据的原因么。。其实hive metastore的代码从大的来看，就好比元数据的增删改查，从上次梳理中我们看到，在创建HiveMetaStore的init方法中，同时创建了三种Listener---MetaStorePreEventListener，MetaStoreEventListener，MetaStoreEndFunctionListener用于对每一步事件的监听与记录。同时呢，它还new出了WareHouse，用以进行物理操作。

　　

     public void init() throws MetaException {
       rawStoreClassName = hiveConf.getVar(HiveConf.ConfVars.METASTORE_RAW_STORE_IMPL);
       initListeners = MetaStoreUtils.getMetaStoreListeners(
           MetaStoreInitListener.class, hiveConf,
           hiveConf.getVar(HiveConf.ConfVars.METASTORE_INIT_HOOKS));
       for (MetaStoreInitListener singleInitListener: initListeners) {
           MetaStoreInitContext context = new MetaStoreInitContext();
           singleInitListener.onInit(context);
       }

       String alterHandlerName = hiveConf.get("hive.metastore.alter.impl",
           HiveAlterHandler.class.getName());
       alterHandler = (AlterHandler) ReflectionUtils.newInstance(MetaStoreUtils.getClass(
           alterHandlerName), hiveConf);
       wh = new Warehouse(hiveConf);
         。。。。
     }

　接下来，我们从元数据的生命周期开始，学习下Partiiton的生命周期。在HiveMetaStoreClient中，查找add_partition作为入口，这种操作在我们insert overwrite 以表中某个字段为分区时，比如dt=20170830，作用到的操作。或者是add_partitions，创建分区表后进行数据的导入，那么会创建多个分区路径，下面以add_partiitons为例：

   public int add_partitions(List<Partition> new_parts)
       throws InvalidObjectException, AlreadyExistsException, MetaException,
       TException {
     return client.add_partitions(new_parts);
   }

   @Override
   public List<Partition> add_partitions(
       List<Partition> parts, boolean ifNotExists, boolean needResults)
       throws InvalidObjectException, AlreadyExistsException, MetaException, TException {
     if (parts.isEmpty()) {
       return needResults ? new ArrayList<Partition>() : null;
     }
     Partition part = parts.get(0);
     AddPartitionsRequest req = new AddPartitionsRequest(
16         part.getDbName(), part.getTableName(), parts, ifNotExists);
17     req.setNeedResult(needResults);
18     AddPartitionsResult result = client.add_partitions_req(req);
     return needResults ? filterHook.filterPartitions(result.getPartitions()) : null;
   }

　　这里的client来自于ThriftHiveMetastore.Iface接口对象，其实现子类HiveMetaStore并调用init方法进行创建。随后将封装了AddPartitionsRequest类，其实这个类还是partition的属性，但是这样封装的好处是，今后再调用的时候不用再去获取partition的DbName,,TableName等信息，一次性封装以便后续直接使用该对象。随后，我们查看client调用add_partitions_req,下面代码高能预警，非常多，我们一点点分析。

　　

    private List<Partition> add_partitions_core(
         RawStore ms, String dbName, String tblName, List<Partition> parts, boolean ifNotExists)
             throws MetaException, InvalidObjectException, AlreadyExistsException, TException {
       logInfo("add_partitions");
       boolean success = false;
       // Ensures that the list doesn't have dups, and keeps track of directories we have created.
       Map<PartValEqWrapper, Boolean> addedPartitions = new HashMap<PartValEqWrapper, Boolean>();
       List<Partition> result = new ArrayList<Partition>();
       List<Partition> existingParts = null;
       Table tbl = null;
       try {
         ms.openTransaction();
         tbl = ms.getTable(dbName, tblName);
         if (tbl == null) {
           throw new InvalidObjectException("Unable to add partitions because "
               + "database or table " + dbName + "." + tblName + " does not exist");
         }

         if (!parts.isEmpty()) {
           firePreEvent(new PreAddPartitionEvent(tbl, parts, this));
         }

         for (Partition part : parts) {
           if (!part.getTableName().equals(tblName) || !part.getDbName().equals(dbName)) {
             throw new MetaException("Partition does not belong to target table "
                 + dbName + "." + tblName + ": " + part);
           }
           boolean shouldAdd = startAddPartition(ms, part, ifNotExists);
           if (!shouldAdd) {
             if (existingParts == null) {
               existingParts = new ArrayList<Partition>();
             }
             existingParts.add(part);
             LOG.info("Not adding partition " + part + " as it already exists");
             continue;
           }
           boolean madeDir = createLocationForAddedPartition(tbl, part);
           if (addedPartitions.put(new PartValEqWrapper(part), madeDir) != null) {
             // Technically, for ifNotExists case, we could insert one and discard the other
             // because the first one now "exists", but it seems better to report the problem
             // upstream as such a command doesn't make sense.
             throw new MetaException("Duplicate partitions in the list: " + part);
           }
           initializeAddedPartition(tbl, part, madeDir);
           result.add(part);
         }
         if (!result.isEmpty()) {
           success = ms.addPartitions(dbName, tblName, result);
         } else {
           success = true;
         }
         success = success && ms.commitTransaction();
       } finally {
         if (!success) {
           ms.rollbackTransaction();
           for (Entry<PartValEqWrapper, Boolean> e : addedPartitions.entrySet()) {
             if (e.getValue()) {
               wh.deleteDir(new Path(e.getKey().partition.getSd().getLocation()), true);
               // we just created this directory - it's not a case of pre-creation, so we nuke
             }
           }
           fireMetaStoreAddPartitionEvent(tbl, parts, null, false);
         } else {
           fireMetaStoreAddPartitionEvent(tbl, result, null, true);
           if (existingParts != null) {
             // The request has succeeded but we failed to add these partitions.
             fireMetaStoreAddPartitionEvent(tbl, existingParts, null, false);
           }
         }
       }
       return result;
     }

　　首先呢

　　1、ms.openTransaction()，这个上次已经提到过，是为了保证操作的原子性。随后 tbl = ms.getTable(dbName, tblName);

　　2、通过dbName以及tableName获取正个Table对象。

　　3、通过firePreEvent记录事件。

　　4、开始循环遍历partiiton,通过startAddPartition方法校验该partition是否在元数据中存在

　　5、调用createLocationForAddedPartition方法进行文件路径创建，随后调用initializeAddedPartition，主要是将table的param信息赋给partition，与hive的表结构有关，最终会将param扩展信息写入类似meta_partition_param的扩展信息表。

　　6、待物理操作完毕之后，进行ms.addPartitions(dbName, tblName, result)元数据信息的meta录入。

　　7、如果说partition的路径已经存在，则抛出异常，并且在最后删除已经创建的路径。这个有一次，请看上面，首先创建了一个Map,

Map<PartValEqWrapper, Boolean> addedPartitions = new HashMap<PartValEqWrapper, Boolean>();将partition对象作为key,mkdir成功失败的布尔值作为value,最终通过判断value的值，来删除创建成功的partition.

　　删除，和查询就不说了，因为太过简单，那么alter_partition来了，client.alter_partition(dbName, tblName, newPart);从client端调用我也不说了~，传入dbName，tbleName以及新的partition，随之在hivemetaStore中调用了rename_partition方法：

　　

    @Override
    public void rename_partition(final String db_name, final String tbl_name,
        final List<String> part_vals, final Partition new_part)
        throws InvalidOperationException, MetaException, TException {
      // Call rename_partition without an environment context.
      rename_partition(db_name, tbl_name, part_vals, new_part, null);
    }

    private void rename_partition(final String db_name, final String tbl_name,
        final List<String> part_vals, final Partition new_part,
        final EnvironmentContext envContext)
        throws InvalidOperationException, MetaException,
        TException {
      startTableFunction("alter_partition", db_name, tbl_name);

      if (LOG.isInfoEnabled()) {
        LOG.info("New partition values:" + new_part.getValues());
        if (part_vals != null && part_vals.size() > 0) {
          LOG.info("Old Partition values:" + part_vals);
        }
      }

      Partition oldPart = null;
      Exception ex = null;
      try {
        firePreEvent(new PreAlterPartitionEvent(db_name, tbl_name, part_vals, new_part, this));

        if (part_vals != null && !part_vals.isEmpty()) {
          MetaStoreUtils.validatePartitionNameCharacters(new_part.getValues(),
              partitionValidationPattern);
        }

        oldPart = alterHandler.alterPartition(getMS(), wh, db_name, tbl_name, part_vals, new_part);

        // Only fetch the table if we actually have a listener
        Table table = null;
        for (MetaStoreEventListener listener : listeners) {
          if (table == null) {
            table = getMS().getTable(db_name, tbl_name);
          }
          AlterPartitionEvent alterPartitionEvent =
              new AlterPartitionEvent(oldPart, new_part, table, true, this);
          alterPartitionEvent.setEnvironmentContext(envContext);
          listener.onAlterPartition(alterPartitionEvent);
        }
      } catch (InvalidObjectException e) {
        ex = e;
        throw new InvalidOperationException(e.getMessage());
      } catch (AlreadyExistsException e) {
        ex = e;
        throw new InvalidOperationException(e.getMessage());
      } catch (Exception e) {
        ex = e;
        if (e instanceof MetaException) {
          throw (MetaException) e;
        } else if (e instanceof InvalidOperationException) {
          throw (InvalidOperationException) e;
        } else if (e instanceof TException) {
          throw (TException) e;
        } else {
          throw newMetaException(e);
        }
      } finally {
        endFunction("alter_partition", oldPart != null, ex, tbl_name);
      }
      return;
    }

　　我们继续来看：　　

　　1、startTableFunction方法主要用来计数

　　2、new_part.getValues()其实获取的是partition的具体列值信息，比如dt=20170830，那么获取的就是这个20170830

　　3、随之通过validatePartitionNameCharacters校验partitionName是否合法。

　　4、随后通过alterHandler.alterPartition进行partition的更改，但是为什么要用oldPart命名？已经修改了呀？（疑问）我们跟进去会发现，其调用了updatePartColumnStats方法：

  private void updatePartColumnStats(RawStore msdb, String dbName, String tableName,
      List<String> partVals, Partition newPart) throws MetaException, InvalidObjectException {
    dbName = HiveStringUtils.normalizeIdentifier(dbName);
    tableName = HiveStringUtils.normalizeIdentifier(tableName);
    String newDbName = HiveStringUtils.normalizeIdentifier(newPart.getDbName());
    String newTableName = HiveStringUtils.normalizeIdentifier(newPart.getTableName());

    Table oldTable = msdb.getTable(dbName, tableName);
    if (oldTable == null) {
      return;
    }

    try {
      String oldPartName = Warehouse.makePartName(oldTable.getPartitionKeys(), partVals);
      String newPartName = Warehouse.makePartName(oldTable.getPartitionKeys(), newPart.getValues());
      if (!dbName.equals(newDbName) || !tableName.equals(newTableName)
          || !oldPartName.equals(newPartName)) {
        msdb.deletePartitionColumnStatistics(dbName, tableName, oldPartName, partVals, null);
      } else {
        Partition oldPartition = msdb.getPartition(dbName, tableName, partVals);
        if (oldPartition == null) {
          return;
        }
        if (oldPartition.getSd() != null && newPart.getSd() != null) {
        List<FieldSchema> oldCols = oldPartition.getSd().getCols();
          if (!MetaStoreUtils.areSameColumns(oldCols, newPart.getSd().getCols())) {
            updatePartColumnStatsForAlterColumns(msdb, oldPartition, oldPartName, partVals, oldCols, newPart);
          }
        }
      }
    } catch (NoSuchObjectException nsoe) {
      LOG.debug("Could not find db entry." + nsoe);
      //ignore
    } catch (InvalidInputException iie) {
      throw new InvalidObjectException("Invalid input to update partition column stats." + iie);
    }
  }

　　5、通过Warehouse.makePartName组装partition的原有和新的表达，比如：dt=20180830,新的为dataPart=20180830

　　6、这里会有层判断，如果新的表达与旧的表达不同则删除原有meta信息，否则将会调用updatePartColumnStatsForAlterColumns进行meta元数据的更新。

　　随后就木有了。。太晚了，碎觉啦，明天还要作死上班呢哈哈哈哈~