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：
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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
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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：
1 private IMetaStoreClient createMetaStoreClient() throws MetaException {
2
3 HiveMetaHookLoader hookLoader = new HiveMetaHookLoader() {
4 @Override
5 public HiveMetaHook getHook(
6 org.apache.hadoop.hive.metastore.api.Table tbl)
7 throws MetaException {
8
9 try {
10 if (tbl == null) {
11 return null;
12 }
13 HiveStorageHandler storageHandler =
14 HiveUtils.getStorageHandler(conf,
15 tbl.getParameters().get(META_TABLE_STORAGE));
16 if (storageHandler == null) {
17 return null;
18 }
19 return storageHandler.getMetaHook();
20 } catch (HiveException ex) {
21 LOG.error(StringUtils.stringifyException(ex));
22 throw new MetaException(
23 "Failed to load storage handler: " + ex.getMessage());
24 }
25 }
26 };
27 return RetryingMetaStoreClient.getProxy(conf, hookLoader, metaCallTimeMap,
28 SessionHiveMetaStoreClient.class.getName());
29 }
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。
1 public void createTable(Table tbl, EnvironmentContext envContext) throws AlreadyExistsException,
2 InvalidObjectException, MetaException, NoSuchObjectException, TException {
3 HiveMetaHook hook = getHook(tbl);
4 if (hook != null) {
5 hook.preCreateTable(tbl);
6 }
7 boolean success = false;
8 try {
9 // Subclasses can override this step (for example, for temporary tables)
10 create_table_with_environment_context(tbl, envContext);
11 if (hook != null) {
12 hook.commitCreateTable(tbl);
13 }
14 success = true;
15 } finally {
16 if (!success && (hook != null)) {
17 hook.rollbackCreateTable(tbl);
18 }
19 }
20 }
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:
1 public HiveMetaStoreClient(HiveConf conf, HiveMetaHookLoader hookLoader)
2 throws MetaException {
3
4 this.hookLoader = hookLoader;
5 if (conf == null) {
6 conf = new HiveConf(HiveMetaStoreClient.class);
7 }
8 this.conf = conf;
9 filterHook = loadFilterHooks();
10
11 String msUri = conf.getVar(HiveConf.ConfVars.METASTOREURIS);
12 localMetaStore = HiveConfUtil.isEmbeddedMetaStore(msUri);
13 if (localMetaStore) {
14 // instantiate the metastore server handler directly instead of connecting
15 // through the network
16 client = HiveMetaStore.newRetryingHMSHandler("hive client", conf, true);
17 isConnected = true;
18 snapshotActiveConf();
19 return;
20 }
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。
1 initListeners = MetaStoreUtils.getMetaStoreListeners(
2 MetaStoreInitListener.class, hiveConf,
3 hiveConf.getVar(HiveConf.ConfVars.METASTORE_INIT_HOOKS));
4 for (MetaStoreInitListener singleInitListener: initListeners) {
5 MetaStoreInitContext context = new MetaStoreInitContext();
6 singleInitListener.onInit(context);
7 }
8
9 String alterHandlerName = hiveConf.get("hive.metastore.alter.impl",
10 HiveAlterHandler.class.getName());
11 alterHandler = (AlterHandler) ReflectionUtils.newInstance(MetaStoreUtils.getClass(
12 alterHandlerName), hiveConf);
13 wh = new Warehouse(hiveConf);
14
15 synchronized (HMSHandler.class) {
16 if (currentUrl == null || !currentUrl.equals(MetaStoreInit.getConnectionURL(hiveConf))) {
17 createDefaultDB();
18 createDefaultRoles();
19 addAdminUsers();
20 currentUrl = MetaStoreInit.getConnectionURL(hiveConf);
21 }
22 }
23
24 if (hiveConf.getBoolean("hive.metastore.metrics.enabled", false)) {
25 try {
26 Metrics.init();
27 } catch (Exception e) {
28 // log exception, but ignore inability to start
29 LOG.error("error in Metrics init: " + e.getClass().getName() + " "
30 + e.getMessage(), e);
31 }
32 }
33
34 preListeners = MetaStoreUtils.getMetaStoreListeners(MetaStorePreEventListener.class,
35 hiveConf,
36 hiveConf.getVar(HiveConf.ConfVars.METASTORE_PRE_EVENT_LISTENERS));
37 listeners = MetaStoreUtils.getMetaStoreListeners(MetaStoreEventListener.class, hiveConf,
38 hiveConf.getVar(HiveConf.ConfVars.METASTORE_EVENT_LISTENERS));
39 listeners.add(new SessionPropertiesListener(hiveConf));
40 endFunctionListeners = MetaStoreUtils.getMetaStoreListeners(
41 MetaStoreEndFunctionListener.class, hiveConf,
42 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。。）。
1 public interface AlterHandler extends Configurable {
2
3 /**
4 * handles alter table
5 *
6 * @param msdb
7 * object to get metadata
8 * @param wh
9 * TODO
10 * @param dbname
11 * database of the table being altered
12 * @param name
13 * original name of the table being altered. same as
14 * <i>newTable.tableName</i> if alter op is not a rename.
15 * @param newTable
16 * new table object
17 * @throws InvalidOperationException
18 * thrown if the newTable object is invalid
19 * @throws MetaException
20 * thrown if there is any other error
21 */
22 public abstract void alterTable(RawStore msdb, Warehouse wh, String dbname,
23 String name, Table newTable) throws InvalidOperationException,
24 MetaException;
25
26 /**
27 * handles alter table, the changes could be cascaded to partitions if applicable
28 *
29 * @param msdb
30 * object to get metadata
31 * @param wh
32 * Hive Warehouse where table data is stored
33 * @param dbname
34 * database of the table being altered
35 * @param name
36 * original name of the table being altered. same as
37 * <i>newTable.tableName</i> if alter op is not a rename.
38 * @param newTable
39 * new table object
40 * @param cascade
41 * if the changes will be cascaded to its partitions if applicable
42 * @throws InvalidOperationException
43 * thrown if the newTable object is invalid
44 * @throws MetaException
45 * thrown if there is any other error
46 */
47 public abstract void alterTable(RawStore msdb, Warehouse wh, String dbname,
48 String name, Table newTable, boolean cascade) throws InvalidOperationException,
49 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。
1 @Override
2 public void createDatabase(Database db) throws InvalidObjectException, MetaException {
3 boolean commited = false;
4 MDatabase mdb = new MDatabase();
5 mdb.setName(db.getName().toLowerCase());
6 mdb.setLocationUri(db.getLocationUri());
7 mdb.setDescription(db.getDescription());
8 mdb.setParameters(db.getParameters());
9 mdb.setOwnerName(db.getOwnerName());
10 PrincipalType ownerType = db.getOwnerType();
11 mdb.setOwnerType((null == ownerType ? PrincipalType.USER.name() : ownerType.name()));
12 try {
13 openTransaction();
14 pm.makePersistent(mdb);
15 commited = commitTransaction();
16 } finally {
17 if (!commited) {
18 rollbackTransaction();
19 }
20 }
21 }
22
23 @SuppressWarnings("nls")
24 private MDatabase getMDatabase(String name) throws NoSuchObjectException {
25 MDatabase mdb = null;
26 boolean commited = false;
27 try {
28 openTransaction();
29 name = HiveStringUtils.normalizeIdentifier(name);
30 Query query = pm.newQuery(MDatabase.class, "name == dbname");
31 query.declareParameters("java.lang.String dbname");
32 query.setUnique(true);
33 mdb = (MDatabase) query.execute(name);
34 pm.retrieve(mdb);
35 commited = commitTransaction();
36 } finally {
37 if (!commited) {
38 rollbackTransaction();
39 }
40 }
41 if (mdb == null) {
42 throw new NoSuchObjectException("There is no database named " + name);
43 }
44 return mdb;
45 }
今晚就到这里。。。自己摸索，如有错误，还望指出谢谢~
