java - Hibernate 批量大小混淆

Question

这个程序一个接一个地执行数以万计的连续插入。我以前从未使用过 hibernate 。我的性能非常慢(如果我只是手动连接并执行 SQL，我的速度会快 10-12 倍。根据许多 hibernate 教程，我的 batch_size 设置为 50。

这是来自单个插入的日志 - 也许您可以帮助我准确了解正在发生的事情:

START INSERT
11:02:56.121 [main] DEBUG org.hibernate.impl.SessionImpl - opened session at timestamp: 13106053761                                                                                            
11:02:56.121 [main] DEBUG o.h.transaction.JDBCTransaction - begin                                                                                                                               
11:02:56.121 [main] DEBUG org.hibernate.jdbc.ConnectionManager - opening JDBC connection                                                                                                             
11:02:56.121 [main] TRACE o.h.c.DriverManagerConnectionProvider - total checked-out connections: 0                                                                                                    
11:02:56.121 [main] TRACE o.h.c.DriverManagerConnectionProvider - using pooled JDBC connection, pool size: 0                                                                                          
11:02:56.121 [main] DEBUG o.h.transaction.JDBCTransaction - current autocommit status: false                                                                                                    
11:02:56.121 [main] TRACE org.hibernate.jdbc.JDBCContext - after transaction begin                                                                                                             
11:02:56.121 [main] TRACE org.hibernate.impl.SessionImpl - setting flush mode to: MANUAL                                                                                                       
11:02:56.121 [main] TRACE o.h.e.def.DefaultLoadEventListener - loading entity: [com.xyzcompany.foo.edoi.ejb.msw000.MSW000Rec#component[keyW000]{keyW000=F000    ADSUFC}]                           
11:02:56.121 [main] TRACE o.h.e.def.DefaultLoadEventListener - creating new proxy for entity                                                                                                       
11:02:56.122 [main] TRACE o.h.e.d.DefaultSaveOrUpdateEventListener - saving transient instance                                                                                                           
11:02:56.122 [main] DEBUG o.h.e.def.AbstractSaveEventListener - generated identifier: component[keyW000]{keyW000=F000    ADSUFC}, using strategy: org.hibernate.id.CompositeNestedGeneratedValueGenerator
11:02:56.122 [main] TRACE o.h.e.def.AbstractSaveEventListener - saving [com.xyzcompany.foo.edoi.ejb.msw000.MSW000Rec#component[keyW000]{keyW000=F000    ADSUFC}]                                    
11:02:56.123 [main] TRACE o.h.e.d.AbstractFlushingEventListener - flushing session                                                                                                                    
11:02:56.123 [main] DEBUG o.h.e.d.AbstractFlushingEventListener - processing flush-time cascades                                                                                                      
11:02:56.123 [main] DEBUG o.h.e.d.AbstractFlushingEventListener - dirty checking collections                                                                                                          
11:02:56.123 [main] TRACE o.h.e.d.AbstractFlushingEventListener - Flushing entities and processing referenced collections                                                                             
11:02:56.125 [main] TRACE o.h.e.d.AbstractFlushingEventListener - Processing unreferenced collections                                                                                                 
11:02:56.125 [main] TRACE o.h.e.d.AbstractFlushingEventListener - Scheduling collection removes/(re)creates/updates                                                                                   
11:02:56.126 [main] DEBUG o.h.e.d.AbstractFlushingEventListener - Flushed: 1 insertions, 0 updates, 0 deletions to 62 objects                                                                         
11:02:56.126 [main] DEBUG o.h.e.d.AbstractFlushingEventListener - Flushed: 0 (re)creations, 0 updates, 0 removals to 0 collections                                                                                                                                                                                       
11:02:56.132 [main] TRACE o.h.e.d.AbstractFlushingEventListener - executing flush                                                                                                                     
11:02:56.132 [main] TRACE org.hibernate.jdbc.ConnectionManager - registering flush begin                                                                                                             
11:02:56.132 [main] TRACE o.h.p.entity.AbstractEntityPersister - Inserting entity: [com.xyzcompany.foo.edoi.ejb.msw000.MSW000Rec#component[keyW000]{keyW000=F000    ADSUFC}]                         
11:02:56.132 [main] DEBUG org.hibernate.jdbc.AbstractBatcher - about to open PreparedStatement (open PreparedStatements: 0, globally: 0)                                                           
11:02:56.132 [main] DEBUG org.hibernate.SQL - insert into MSW000 (W000_DATA_REC, W000_FILE_FLAGS, KEY_W000) values (?, ?, ?)                                                      
11:02:56.132 [main] TRACE org.hibernate.jdbc.AbstractBatcher - preparing statement                                                                                                                 
11:02:56.132 [main] TRACE o.h.p.entity.AbstractEntityPersister - Dehydrating entity: [com.xyzcompany.foo.edoi.ejb.msw000.MSW000Rec#component[keyW000]{keyW000=F000    ADSUFC}]                       
11:02:56.132 [main] TRACE org.hibernate.type.StringType - binding '    ADSUFCA                                                                                                                                                                                                                                                                                  ' to parameter: 1
11:02:56.132 [main] TRACE org.hibernate.type.StringType - binding ' ' to parameter: 2                                                                                                         
11:02:56.132 [main] TRACE org.hibernate.type.StringType - binding 'F000    ADSUFC' to parameter: 3                                                                                            
11:02:56.132 [main] DEBUG org.hibernate.jdbc.AbstractBatcher - Executing batch size: 1                                                                                                             
11:02:56.133 [main] DEBUG org.hibernate.jdbc.AbstractBatcher - about to close PreparedStatement (open PreparedStatements: 1, globally: 1)                                                          
11:02:56.133 [main] TRACE org.hibernate.jdbc.AbstractBatcher - closing statement                                                                                                                   
11:02:56.133 [main] TRACE org.hibernate.jdbc.ConnectionManager - registering flush end                                                                                                               
11:02:56.133 [main] TRACE o.h.e.d.AbstractFlushingEventListener - post flush                                                                                                                          
11:02:56.133 [main] DEBUG o.h.transaction.JDBCTransaction - commit                                                                                                                              
11:02:56.133 [main] TRACE org.hibernate.impl.SessionImpl - automatically flushing session                                                                                                      
11:02:56.133 [main] TRACE org.hibernate.jdbc.JDBCContext - before transaction completion                                                                                                       
11:02:56.133 [main] TRACE org.hibernate.impl.SessionImpl - before transaction completion                                                                                                       
11:02:56.133 [main] DEBUG o.h.transaction.JDBCTransaction - committed JDBC Connection                                                                                                           
11:02:56.133 [main] TRACE org.hibernate.jdbc.JDBCContext - after transaction completion                                                                                                        
11:02:56.133 [main] DEBUG org.hibernate.jdbc.ConnectionManager - transaction completed on session with on_close connection release mode; be sure to close the session to release JDBC resources!     
11:02:56.133 [main] TRACE org.hibernate.impl.SessionImpl - after transaction completion                                                                                                        
11:02:56.133 [main] TRACE org.hibernate.impl.SessionImpl - closing session                                                                                                                     
11:02:56.133 [main] TRACE org.hibernate.jdbc.ConnectionManager - performing cleanup                                                                                                                  
11:02:56.133 [main] DEBUG org.hibernate.jdbc.ConnectionManager - releasing JDBC connection [ (open PreparedStatements: 0, globally: 0) (open ResultSets: 0, globally: 0)]                            
11:02:56.133 [main] TRACE o.h.c.DriverManagerConnectionProvider - returning connection to pool, pool size: 1                                                                                          
11:02:56.133 [main] TRACE org.hibernate.jdbc.JDBCContext - after transaction completion                                                                                                        
11:02:56.133 [main] DEBUG org.hibernate.jdbc.ConnectionManager - transaction completed on session with on_close connection release mode; be sure to close the session to release JDBC resources!     
11:02:56.134 [main] TRACE org.hibernate.impl.SessionImpl - after transaction completion                                                                                                        
FINISH INSERT

Answer 1

当你调用 session.save() 时，hibernate 会生成一个 INSERT SQL。此 INSERT SQL 将在刷新期间附加到数据库(即 session.flush())。

在刷新期间，如果 hibernate.jdbc.batch_size 设置为某个非零值，Hibernate 将使用 JDBC2 API 中引入的批处理功能向 DB 发出批量插入 SQL。

例如，如果您 save() 100 条记录并且您的 hibernate.jdbc.batch_size 设置为 50。在刷新期间，而不是发出以下 SQL 100 次:

insert into TableA (id , fields) values (1, 'val1');
insert into TableA (id , fields) values (2, 'val2');
insert into TableA (id , fields) values (3, 'val3');
.........................
insert into TableA (id , fields) values (100, 'val100');

Hiberate 会将它们分组为 50 个批处理，并且只向 DB 发出 2 个 SQL，如下所示:

insert into TableA (id , fields) values (1, 'val1') , (2, 'val2') ,(3, 'val3') ,(4, 'val4') ,......,(50, 'val50')
insert into TableA (id , fields) values (51, 'val51') , (52, 'val52') ,(53, 'val53') ,(54, 'val54'),...... ,(100, 'val100')  

请注意，如果插入表的主键是GenerationType.Identity，Hibernate 会在 JDBC 级别透明地禁用插入批处理。

从您的日志中:您 save() 只有一条记录，然后是 flush()，因此每次刷新只有一个附加的 INSERT SQL 需要处理。这就是为什么 Hibernate 不能帮助您批量插入，因为只有一个 INSERT SQL 需要处理。您应该在调用 flush() 之前 save() 达到一定数量的记录，而不是为每个 save 调用 flush() ()。

批量插入的最佳实践是这样的:

Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();
for  ( int i=0; i<888888; i++ ) {
  TableA record = new TableA();
    record.setXXXX();
    session.save(record)
    if ( i % 50 == 0 ) { //50, same as the JDBC batch size
        //flush a batch of inserts and release memory:
        session.flush();
        session.clear();
    }
}
tx.commit();
session.close();

您逐批保存和刷新记录。在每个批处理结束时，您应该清除持久性上下文以释放一些内存，以防止内存耗尽，因为每个持久性对象都被放入第一级缓存(您的 JVM 内存)。您还可以禁用二级缓存以减少不必要的开销。

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引用:

• Official Hibernate Documentation : Chapter 14. Batch processing
• Hibernate Batch Processing – Why you may not be using it. (Even if you think you are)