批量插入(Batch inserts)
如果要將很多對象持久化,你必須通過經常的調用 flush() 以及稍後調用 clear() 來控制第一級緩存的大小,防止內存溢出異常。
Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();
ScrollableResults users = session.getNamedQuery("GetUsers")
.setCacheMode(CacheMode.IGNORE)
.scroll(ScrollMode.FORWARD_ONLY);
int count=0;
while ( users.next() ) {
User user= (User) users.get(0);
user.updateStuff(...);
if ( ++count % 20 == 0 ) {
//flush a batch of updates and release memory:
session.flush();
session.clear();
}
}
tx.commit();
session.close();
批量更新(Batch update)
此方法同樣適用於檢索和更新數據。此外,在進行會返回很多行數據的查詢時, 你需要使用 scroll() 方法以便充分利用服務器端遊標所帶來的好處。
Session session = sessionFactory.openSession();
Transaction tx = session.beginTransaction();
ScrollableResults users = session.getNamedQuery("GetUsers")
.setCacheMode(CacheMode.IGNORE)
.scroll(ScrollMode.FORWARD_ONLY);
int count=0;
while ( users.next() ) {
User user= (User) users.get(0);
user.updateStuff(...);
if ( ++count % 20 == 0 ) {
//flush a batch of updates and release memory:
session.flush();
session.clear();
}
}
tx.commit();
session.close();