不要问我为什么，因为爱，哈哈哈哈。。。进入正题，最近做项目顺带学习了下hive metastore的源码，进行下知识总结。
hive metastore的整体架构如图：
一、组成结构：
如图我们可以看到，hive metastore的组成结构分为 客户端 服务端 ，那么下来我们逐一进行分析：
1、客户端
从代码的角度来看：尼玛太多了。。我们从入口HIVE开始看，可以找到MetaStoreClient客户端的创建：
private IMetaStoreClient createMetaStoreClient() throws MetaException {
HiveMetaHookLoader hookLoader = new HiveMetaHookLoader() {
@Override
public HiveMetaHook getHook(
org.apache.hadoop.hive.metastore.api.Table tbl)
throws MetaException {
try {
if (tbl == null) {
return null;
}
HiveStorageHandler storageHandler =
HiveUtils.getStorageHandler(conf,
tbl.getParameters().get(META_TABLE_STORAGE));
if (storageHandler == null) {
return null;
}
return storageHandler.getMetaHook();
} catch (HiveException ex) {
LOG.error(StringUtils.stringifyException(ex));
throw new MetaException(
"Failed to load storage handler: " + ex.getMessage());
}
}
};
return RetryingMetaStoreClient.getProxy(conf, hookLoader, metaCallTimeMap,
SessionHiveMetaStoreClient.class.getName());
}
我们可以看到，创建MetaStoreClient中，创建了HiveMetaHook,这个Hook的作用在于，每次对meta进行操作的时候，比如createTable的时候，如果建表的存储方式不是文件，比如集成hbase，HiveMetaStoreClient会调用hook的接口方法preCreateTable，进行建表前的准备，用来判断外部表与内部表，如果中途有失败的话，依旧调用hook中的rollbackCreateTable进行回滚。
public void createTable(Table tbl, EnvironmentContext envContext) throws AlreadyExistsException,
InvalidObjectException, MetaException, NoSuchObjectException, TException {
HiveMetaHook hook = getHook(tbl);
if (hook != null) {
hook.preCreateTable(tbl);
}
boolean success = false;
try {
// Subclasses can override this step (for example, for temporary tables)
create_table_with_environment_context(tbl, envContext);
if (hook != null) {
hook.commitCreateTable(tbl);
}
success = true;
} finally {
if (!success && (hook != null)) {
hook.rollbackCreateTable(tbl);
}
}
}
在hbase表不存在的情况下，不能create external table ,会报doesn't exist while the table is declared as an external table,那么需直接创建create table 创建一个指向hbase的hive表。
建表语句如下：
CREATE TABLE hbase_table_1(key int, value string) /
STORED BY 'org.apache.hadoop.hive.hbase.HBaseStorageHandler'
WITH SERDEPROPERTIES ("hbase.columns.mapping" = ":key,cf1:val")
TBLPROPERTIES ("hbase.table.name" = "tableName", "hbase.mapred.output.outputtable" = "tableName");
代码请查看HBaseStorageHandler的preCreateTable方法，这里就不贴出来啦。
随之回归Hive类，Hive类可以说是整个元数据DDL操作的最顶层抽象。HiveMetaStoreClient实现了IMetaStoreClient的接口，在创建HiveMetaStoreClient时，会创建于server段HiveMetaStore的链接，并且会通过检查hive.metastore.local是否为true,来决定是在本地创建服务端，这里为在本地:
public HiveMetaStoreClient(HiveConf conf, HiveMetaHookLoader hookLoader)
throws MetaException { this.hookLoader = hookLoader;
if (conf == null) {
conf = new HiveConf(HiveMetaStoreClient.class);
}
this.conf = conf;
filterHook = loadFilterHooks(); String msUri = conf.getVar(HiveConf.ConfVars.METASTOREURIS);
localMetaStore = HiveConfUtil.isEmbeddedMetaStore(msUri);
if (localMetaStore) {
// instantiate the metastore server handler directly instead of connecting
// through the network
client = HiveMetaStore.newRetryingHMSHandler("hive client", conf, true);
isConnected = true;
snapshotActiveConf();
return;
}
随后，创建server端的HiveMetaStore.HMSHandler，HMSHandler继承自IHMSHandler，而IHMSHandler又继承自ThriftHiveMetastore.Iface，在HMSHandler中实现了所有操作的对外方法：
public class ThriftHiveMetastore {
/**
* This interface is live.
*/
public interface Iface extends com.facebook.fb303.FacebookService.Iface {
public String getMetaConf(String key) throws MetaException, org.apache.thrift.TException;
public void setMetaConf(String key, String value) throws MetaException, org.apache.thrift.TException;
public void create_database(Database database) throws AlreadyExistsException, InvalidObjectException, MetaException, org.apache.thrift.TException;
public Database get_database(String name) throws NoSuchObjectException, MetaException, org.apache.thrift.TException;
public void drop_database(String name, boolean deleteData, boolean cascade) throws NoSuchObjectException, InvalidOperationException, MetaException, org.apache.thrift.TException;
public List<String> get_databases(String pattern) throws MetaException, org.apache.thrift.TException;
public List<String> get_all_databases() throws MetaException, org.apache.thrift.TException;
public void alter_database(String dbname, Database db) throws MetaException, NoSuchObjectException, org.apache.thrift.TException;
public Type get_type(String name) throws MetaException, NoSuchObjectException, org.apache.thrift.TException;
public boolean create_type(Type type) throws AlreadyExistsException, InvalidObjectException, MetaException, org.apache.thrift.TException;
public boolean drop_type(String type) throws MetaException, NoSuchObjectException, org.apache.thrift.TException;
......
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。
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); synchronized (HMSHandler.class) {
if (currentUrl == null || !currentUrl.equals(MetaStoreInit.getConnectionURL(hiveConf))) {
createDefaultDB();
createDefaultRoles();
addAdminUsers();
currentUrl = MetaStoreInit.getConnectionURL(hiveConf);
}
} if (hiveConf.getBoolean("hive.metastore.metrics.enabled", false)) {
try {
Metrics.init();
} catch (Exception e) {
// log exception, but ignore inability to start
LOG.error("error in Metrics init: " + e.getClass().getName() + " "
+ e.getMessage(), e);
}
} preListeners = MetaStoreUtils.getMetaStoreListeners(MetaStorePreEventListener.class,
hiveConf,
hiveConf.getVar(HiveConf.ConfVars.METASTORE_PRE_EVENT_LISTENERS));
listeners = MetaStoreUtils.getMetaStoreListeners(MetaStoreEventListener.class, hiveConf,
hiveConf.getVar(HiveConf.ConfVars.METASTORE_EVENT_LISTENERS));
listeners.add(new SessionPropertiesListener(hiveConf));
endFunctionListeners = MetaStoreUtils.getMetaStoreListeners(
MetaStoreEndFunctionListener.class, hiveConf,
hiveConf.getVar(HiveConf.ConfVars.METASTORE_END_FUNCTION_LISTENERS));
同时创建了AlterHandler，它是HiveAlterHandler的接口，是将修改表和修改partition的操作抽离了出来单独实现（修改表很复杂的。。）。
public interface AlterHandler extends Configurable {
/**
* handles alter table
*
* @param msdb
* object to get metadata
* @param wh
* TODO
* @param dbname
* database of the table being altered
* @param name
* original name of the table being altered. same as
* <i>newTable.tableName</i> if alter op is not a rename.
* @param newTable
* new table object
* @throws InvalidOperationException
* thrown if the newTable object is invalid
* @throws MetaException
* thrown if there is any other error
*/
public abstract void alterTable(RawStore msdb, Warehouse wh, String dbname,
String name, Table newTable) throws InvalidOperationException,
MetaException;
/**
* handles alter table, the changes could be cascaded to partitions if applicable
*
* @param msdb
* object to get metadata
* @param wh
* Hive Warehouse where table data is stored
* @param dbname
* database of the table being altered
* @param name
* original name of the table being altered. same as
* <i>newTable.tableName</i> if alter op is not a rename.
* @param newTable
* new table object
* @param cascade
* if the changes will be cascaded to its partitions if applicable
* @throws InvalidOperationException
* thrown if the newTable object is invalid
* @throws MetaException
* thrown if there is any other error
*/
public abstract void alterTable(RawStore msdb, Warehouse wh, String dbname,
String name, Table newTable, boolean cascade) throws InvalidOperationException,
MetaException;
最重要的是RawStore的创建。RawStore不光是定义了一套最终的物理操作，使用JDO将一个对象当作表进行存储。ObjectStore中的transaction机制也是通过JDO提供的transaction实现的。当commit失败时，将rollback所有操作。
@Override
public void createDatabase(Database db) throws InvalidObjectException, MetaException {
boolean commited = false;
MDatabase mdb = new MDatabase();
mdb.setName(db.getName().toLowerCase());
mdb.setLocationUri(db.getLocationUri());
mdb.setDescription(db.getDescription());
mdb.setParameters(db.getParameters());
mdb.setOwnerName(db.getOwnerName());
PrincipalType ownerType = db.getOwnerType();
mdb.setOwnerType((null == ownerType ? PrincipalType.USER.name() : ownerType.name()));
try {
openTransaction();
pm.makePersistent(mdb);
commited = commitTransaction();
} finally {
if (!commited) {
rollbackTransaction();
}
}
} @SuppressWarnings("nls")
private MDatabase getMDatabase(String name) throws NoSuchObjectException {
MDatabase mdb = null;
boolean commited = false;
try {
openTransaction();
name = HiveStringUtils.normalizeIdentifier(name);
Query query = pm.newQuery(MDatabase.class, "name == dbname");
query.declareParameters("java.lang.String dbname");
query.setUnique(true);
mdb = (MDatabase) query.execute(name);
pm.retrieve(mdb);
commited = commitTransaction();
} finally {
if (!commited) {
rollbackTransaction();
}
}
if (mdb == null) {
throw new NoSuchObjectException("There is no database named " + name);
}
return mdb;
}
今晚就到这里。。。自己摸索，如有错误，还望指出谢谢~