如何避免多线程在Oracle中进行双重插入
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在我的应用程序中，当我将INSERT插入Oracle时，我对双插入有很多例外。
我的测试代码看起来像那样
class SomeClass{
EntityManager em;
Dao dao;
@Override
void insert(String a, String b){
MyObject object =new MyObject(a,b);
dao.insertObject(object);
}
}
class OtherClass{
private final ExecutorService completableFutureExecutor =
new ThreadPoolExecutor(10, 11, 30L, TimeUnit.SECONDS, new SynchronousQueue<>());
public void method() {
Runnable task1 = () -> dao.insert("a","b");
for (int i = 0; i < 5; i++) {
completableFutureExecutor.submit(task1);
}
}
}
在openJpa日志中，我看到类似的东西
240981 JpaPersistenceUnit TRACE [pool-25-thread-3] openjpa.jdbc.SQL - <t 1427395137, conn 1023570122> executing prepstmnt 743213969 SELECT t0.COLUMN1, t0.COLUMN2 FROM TABLE t0 WHERE t0.COLUMN2 = ? AND t0.COLUMN1 = ? [params=(String) a, (String) b]
240983 JpaPersistenceUnit TRACE [pool-25-thread-9] openjpa.jdbc.SQL - <t 1116539025, conn 246735198> executing prepstmnt 468904024 SELECT t0.COLUMN1, t0.COLUMN2 FROM TABLE t0 WHERE t0.COLUMN2 = ? AND t0.COLUMN1 = ? [params=(String) a, (String) b]
240986 JpaPersistenceUnit TRACE [pool-25-thread-5] openjpa.jdbc.SQL - <t 2107513837, conn 1168031715> executing prepstmnt 1872262728 SELECT t0.COLUMN1, t0.COLUMN2 FROM TABLE t0 WHERE t0.COLUMN2 = ? AND t0.COLUMN1 = ? [params=(String) a, (String) b]
240986 JpaPersistenceUnit TRACE [pool-25-thread-1] openjpa.jdbc.SQL - <t 1881630463, conn 2024928498> executing prepstmnt 1258578230 SELECT t0.COLUMN1, t0.COLUMN2 FROM TABLE t0 WHERE t0.COLUMN2 = ? AND t0.COLUMN1 = ? [params=(String) a, (String) b]
240986 JpaPersistenceUnit TRACE [pool-25-thread-7] openjpa.jdbc.SQL - <t 1202968848, conn 1876787130> executing prepstmnt 1733696457 SELECT t0.COLUMN1, t0.COLUMN2 FROM TABLE t0 WHERE t0.COLUMN2 = ? AND t0.COLUMN1 = ? [params=(String) a, (String) b]
240998 JpaPersistenceUnit TRACE [pool-25-thread-9] openjpa.jdbc.SQL - <t 1116539025, conn 246735198> executing prepstmnt 752805342 INSERT INTO TABLE ( COLUMN1, COLUMN2 ) VALUES (?, ?) [params= (String) a, (String) b]
240999 JpaPersistenceUnit TRACE [pool-25-thread-3] openjpa.jdbc.SQL - <t 1427395137, conn 1023570122> executing prepstmnt 1035550395 INSERT INTO TABLE ( COLUMN1, COLUMN2 ) VALUES (?, ?) [params= (String) a, (String) b]
240999 JpaPersistenceUnit TRACE [pool-25-thread-5] openjpa.jdbc.SQL - <t 2107513837, conn 1168031715> executing prepstmnt 1439514282 INSERT INTO TABLE ( COLUMN1, COLUMN2 ) VALUES (?, ?) [params= (String) a, (String) b]
241000 JpaPersistenceUnit TRACE [pool-25-thread-1] openjpa.jdbc.SQL - <t 1881630463, conn 2024928498> executing prepstmnt 1158780577 INSERT INTO TABLE ( COLUMN1, COLUMN2 ) VALUES (?, ?) [params= (String) a, (String) b]
241000 JpaPersistenceUnit TRACE [pool-25-thread-7] openjpa.jdbc.SQL - <t 1202968848, conn 1876787130> executing prepstmnt 1082517334 INSERT INTO TABLE ( COLUMN1, COLUMN2 ) VALUES (?, ?) [params= (String) a, (String) b]
41018 JpaPersistenceUnit TRACE [pool-25-thread-4] openjpa.Runtime - An exception occurred while ending the transaction. This exception will be re-thrown.<openjpa-2.4.0-r422266:1674604 fatal store error> org.apache.openjpa.util.StoreException: The transaction has been rolled back. See the nested exceptions for details on the errors that occurred.
FailedObject: com.test.SomeClass@19df04ab
at org.apache.openjpa.kernel.BrokerImpl.newFlushException(BrokerImpl.java:2368)
at org.apache.openjpa.kernel.BrokerImpl.flush(BrokerImpl.java:2205)
at org.apache.openjpa.kernel.BrokerImpl.flushSafe(BrokerImpl.java:2103)
at org.apache.openjpa.kernel.BrokerImpl.beforeCompletion(BrokerImpl.java:2021)
at org.apache.openjpa.kernel.LocalManagedRuntime.commit(LocalManagedRuntime.java:81)
at org.apache.openjpa.kernel.BrokerImpl.commit(BrokerImpl.java:1526)
at org.apache.openjpa.kernel.DelegatingBroker.commit(DelegatingBroker.java:932)
at org.apache.openjpa.persistence.EntityManagerImpl.commit(EntityManagerImpl.java:569)
at org.springframework.orm.jpa.JpaTransactionManager.doCommit(JpaTransactionManager.java:514)
at org.springframework.transaction.support.AbstractPlatformTransactionManager.processCommit(AbstractPlatformTransactionManager.java:755)
at org.springframework.transaction.support.AbstractPlatformTransactionManager.commit(AbstractPlatformTransactionManager.java:724)
at org.springframework.transaction.interceptor.TransactionAspectSupport.commitTransactionAfterReturning(TransactionAspectSupport.java:475)
at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:270)
at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:94)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:633)
at com.test.Dao$$EnhancerBySpringCGLIB$$c4aa5f08.insertObject(<generated>)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:317)
at org.springframework.osgi.service.importer.support.internal.aop.ServiceInvoker.doInvoke(ServiceInvoker.java:58)
at org.springframework.osgi.service.importer.support.internal.aop.ServiceInvoker.invoke(ServiceInvoker.java:62)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
at org.springframework.aop.support.DelegatingIntroductionInterceptor.doProceed(DelegatingIntroductionInterceptor.java:132)
at org.springframework.aop.support.DelegatingIntroductionInterceptor.invoke(DelegatingIntroductionInterceptor.java:120)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
at org.springframework.osgi.service.util.internal.aop.ServiceTCCLInterceptor.invokeUnprivileged(ServiceTCCLInterceptor.java:56)
at org.springframework.osgi.service.util.internal.aop.ServiceTCCLInterceptor.invoke(ServiceTCCLInterceptor.java:39)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
at org.springframework.osgi.service.importer.support.LocalBundleContextAdvice.invoke(LocalBundleContextAdvice.java:59)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
at org.springframework.aop.support.DelegatingIntroductionInterceptor.doProceed(DelegatingIntroductionInterceptor.java:132)
at org.springframework.aop.support.DelegatingIntroductionInterceptor.invoke(DelegatingIntroductionInterceptor.java:120)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:204)
at com.sun.proxy.$Proxy255.insertObject(Unknown Source)
at com.test.OtherClass.lambda$method$5(OtherClass.java:146)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
Caused by: <openjpa-2.4.0-r422266:1674604 fatal store error> org.apache.openjpa.util.ObjectExistsException: ORA-00001: unique constraint (TABLE_PK) violated
{prepstmnt 1119780936 INSERT INTO TABLE (COLUMN1, COLUMN2) VALUES (?, ?) [params=(String) a, (String) b]} [code=1, state=23000]
FailedObject: com.test.entities.Table@19df04ab
at org.apache.openjpa.jdbc.sql.DBDictionary.narrow(DBDictionary.java:4986)
at org.apache.openjpa.jdbc.sql.DBDictionary.newStoreException(DBDictionary.java:4961)
at org.apache.openjpa.jdbc.sql.SQLExceptions.getStore(SQLExceptions.java:133)
at org.apache.openjpa.jdbc.sql.SQLExceptions.getStore(SQLExceptions.java:75)
at org.apache.openjpa.jdbc.kernel.BatchingPreparedStatementManagerImpl.flushBatch(BatchingPreparedStatementManagerImpl.java:225)
at org.apache.openjpa.jdbc.kernel.BatchingConstraintUpdateManager.flush(BatchingConstraintUpdateManager.java:63)
at org.apache.openjpa.jdbc.kernel.AbstractUpdateManager.flush(AbstractUpdateManager.java:104)
at org.apache.openjpa.jdbc.kernel.AbstractUpdateManager.flush(AbstractUpdateManager.java:77)
at org.apache.openjpa.jdbc.kernel.JDBCStoreManager.flush(JDBCStoreManager.java:731)
at org.apache.openjpa.kernel.DelegatingStoreManager.flush(DelegatingStoreManager.java:131)
... 43 more
Caused by: org.apache.openjpa.lib.jdbc.ReportingSQLException: ORA-00001: unique constraint (TABLE_PK) violated
{prepstmnt 1119780936 INSERT INTO TABLE (COLUMN1, COLUMN2) VALUES (?, ?) [params=(String) a, (String) b]} [code=1, state=23000]
at org.apache.openjpa.lib.jdbc.LoggingConnectionDecorator.wrap(LoggingConnectionDecorator.java:218)
at org.apache.openjpa.lib.jdbc.LoggingConnectionDecorator.wrap(LoggingConnectionDecorator.java:194)
at org.apache.openjpa.lib.jdbc.LoggingConnectionDecorator.access$1000(LoggingConnectionDecorator.java:58)
at org.apache.openjpa.lib.jdbc.LoggingConnectionDecorator$LoggingConnection$LoggingPreparedStatement.executeUpdate(LoggingConnectionDecorator.java:1133)
at org.apache.openjpa.lib.jdbc.DelegatingPreparedStatement.executeUpdate(DelegatingPreparedStatement.java:275)
at org.apache.openjpa.jdbc.kernel.JDBCStoreManager$CancelPreparedStatement.executeUpdate(JDBCStoreManager.java:1791)
at org.apache.openjpa.jdbc.kernel.PreparedStatementManagerImpl.executeUpdate(PreparedStatementManagerImpl.java:268)
at org.apache.openjpa.jdbc.kernel.BatchingPreparedStatementManagerImpl.flushSingleRow(BatchingPreparedStatementManagerImpl.java:254)
at org.apache.openjpa.jdbc.kernel.BatchingPreparedStatementManagerImpl.flushBatch(BatchingPreparedStatementManagerImpl.java:157)
... 48 more我怎么能避免这种情况？因为很多错误都像我在制作中那样。
UPD在代码段中添加了新的日志。
我的应用程序位于两个服务器（节点）上。每台服务器都连接到DB。所以，我的测试我们可以乘以2。
答案
您可以同步您的doa对象，这意味着它一次只能由一个线程运行。
@Override
void insert(String a, String b) {
MyObject object = new MyObject(a, b);
synchronized (dao) {
dao.insertObject(object);
}
}
像上面这样的东西
synchronized关键字的主要优点是我们可以解决数据不一致问题。但是synchronized关键字的主要缺点是它增加了线程的等待时间并影响了系统的性能。因此，如果没有特定要求，则永远不建议使用synchronized关键字。
另一答案
从并发线程中使用单个EntityManager很可能是一个坏主意，正如您可能从日志中看到的那样：最好的情况是一个线程中的异常回滚EM的单个事务，其他所有线程也尝试使用它。最坏的情况是各种并发问题，竞争条件等等。
我只想INSERT一次，如果已经在DB中，请选择它。但是我在不同的类中有大约5个方法可以及时调用INSERT，因此，应该处理该异常
在这种情况下，除了通过其他方式同步DAO呼叫之外，您可能别无选择;可以通过锁定DB中的某些现有记录或以任何其他方式完成。您可能还想尝试EntityManager.merge()，但我认为这不会解决您同时写两台独立机器的问题。
另一答案
我现在使用memcache，但它不是最终的解决方案
private int expire = 2;
public <T> void insert(Supplier<T> supplier, String... keyLine) throws InterruptedException, MemcachedException, TimeoutException {
String key = ParseUtils.collectToKeyWithDot(keyLine);
T value = getCache(key);
if (value == null) {
value = supplier.get();
setCache(key, value);
}
}
private <T> Boolean setCache(String key, T value) throws InterruptedException, MemcachedException, TimeoutException {
return memcacheClient.set(key, expire, value);
}
private <T> T getCache(String key) throws InterruptedException, MemcachedException, TimeoutException {
return memcacheClient.get(key);
}
在这里，我将我的第一个INSERT存储到DB中，并将其存储到缓存中2秒钟。在那2秒内，如果任何线程尝试将相同的值插入到DB中，则不会发生。首先，它将在缓存中进行检查。对我来说，2秒足以避免异常。
附：我仍在寻找更优雅的解决方案。
另一答案
您可能想要考虑数据访问对象的延迟写入，如下所示 -
class SomeClass {
private EntityManager em;
private Dao dao;
private Set<MyObject> writableObjects = new HashSet<>();
@Override
public void insert(String a, String b) {
MyObject object = new MyObject(a, b);
writableObjects.add(object);
}
@override
public void commit() {
writableObjects.forEach(object -> dao.insertObject(object));
}
}
class OtherClass {
private final ExecutorService completableFutureExecutor = new ThreadPoolExecutor(10, 11, 30L, TimeUnit.SECONDS,
new SynchronousQueue<>());
public void method() {
Runnable task1 = () -> dao.insert("a", "b");
for (int i = 0; i < 5; i++) {
completableFutureExecutor.submit(task1);
}
dao.commit();
}
}
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