Question

我正在尝试在多线程环境（Java 8）中使用orientdb（v2.1.2），其中我从多个线程中更新顶点。我知道orientdb正在使用MVCC，因此这些操作可能会失败并且必须再次执行。

我写了一个小的单元测试，试图通过等待我fork的线程中的循环障碍来激发这种情况。不幸的是，测试失败了一个模糊的异常，我不明白：

Sep 21, 2015 3:00:24 PM com.orientechnologies.common.log.OLogManager log
INFO: OrientDB auto-config DISKCACHE=10,427MB (heap=3,566MB os=16,042MB disk=31,720MB)
Thread [0] running 
Thread [1] running 
Sep 21, 2015 3:00:24 PM com.orientechnologies.common.log.OLogManager log
WARNING: {db=tinkerpop} Requested command 'create edge type 'testedge_1442840424480' as subclass of 'E'' must be executed outside active transaction: the transaction will be committed and reopen right after it. To avoid this behavior execute it outside a transaction
Sep 21, 2015 3:00:24 PM com.orientechnologies.common.log.OLogManager log
WARNING: {db=tinkerpop} Requested command 'create edge type 'testedge_1442840424480' as subclass of 'E'' must be executed outside active transaction: the transaction will be committed and reopen right after it. To avoid this behavior execute it outside a transaction
Exception in thread "Thread-4" com.orientechnologies.orient.core.exception.OSchemaException: Cluster with id 11 already belongs to class testedge_1442840424480
    at com.orientechnologies.orient.core.metadata.schema.OSchemaShared.checkClustersAreAbsent(OSchemaShared.java:1264)
    at com.orientechnologies.orient.core.metadata.schema.OSchemaShared.doCreateClass(OSchemaShared.java:983)
    at com.orientechnologies.orient.core.metadata.schema.OSchemaShared.createClass(OSchemaShared.java:415)
    at com.orientechnologies.orient.core.metadata.schema.OSchemaShared.createClass(OSchemaShared.java:400)
    at com.orientechnologies.orient.core.metadata.schema.OSchemaProxy.createClass(OSchemaProxy.java:100)
    at com.tinkerpop.blueprints.impls.orient.OrientBaseGraph$6.call(OrientBaseGraph.java:1387)
    at com.tinkerpop.blueprints.impls.orient.OrientBaseGraph$6.call(OrientBaseGraph.java:1384)
    at com.tinkerpop.blueprints.impls.orient.OrientBaseGraph.executeOutsideTx(OrientBaseGraph.java:1739)
    at com.tinkerpop.blueprints.impls.orient.OrientBaseGraph.createEdgeType(OrientBaseGraph.java:1384)
    at com.tinkerpop.blueprints.impls.orient.OrientBaseGraph.createEdgeType(OrientBaseGraph.java:1368)
    at com.tinkerpop.blueprints.impls.orient.OrientBaseGraph.createEdgeType(OrientBaseGraph.java:1353)
    at com.tinkerpop.blueprints.impls.orient.OrientVertex.addEdge(OrientVertex.java:928)
    at com.tinkerpop.blueprints.impls.orient.OrientVertex.addEdge(OrientVertex.java:832)
    at com.gentics.test.orientdb.OrientDBTinkerpopMultithreadingTest.lambda$0(OrientDBTinkerpopMultithreadingTest.java:31)
    at com.gentics.test.orientdb.OrientDBTinkerpopMultithreadingTest$$Lambda$1/1446001495.run(Unknown Source)
    at java.lang.Thread.run(Thread.java:745)

测试使用的是简单的内存数据库。我不明白为什么orientdb正在检查一些集群操作：

Cluster with id 11 already belongs to class testedge

只有当我尝试使用相同标签创建两条边时，才会出现此问题。

private OrientGraphFactory factory = new OrientGraphFactory("memory:tinkerpop").setupPool(5, 20);

@Test
public void testConcurrentGraphModifications() throws InterruptedException {
    OrientGraph graph = factory.getTx();
    Vertex v = graph.addVertex(null);
    graph.commit();
    CyclicBarrier barrier = new CyclicBarrier(2);

    List<Thread> threads = new ArrayList<>();

    // Spawn two threads
    for (int i = 0; i < 2; i++) {
        final int threadNo = i;
        threads.add(run(() -> {
            System.out.println("Running thread [" + threadNo + "]");
            // Start a new transaction and modify vertex v
            OrientGraph tx = factory.getTx();
            Vertex v2 = tx.addVertex(null);
            v.addEdge("testedge", v2);
            try {
                barrier.await();
            } catch (Exception e) {
                e.printStackTrace();
            }
            tx.commit();
        }));
    }

    // Wait for all spawned threads
    for (Thread thread : threads) {
        thread.join();
    }
}

protected Thread run(Runnable runnable) {
    Thread thread = new Thread(runnable);
    thread.start();
    return thread;
}

总的来说，我非常感谢一个演示如何在嵌入式多线程Java环境中使用orientdb时处理MVCC冲突的示例。

更新

我注意到当我通过tx.getVertex（vertex.getId（））（而不是通过.reload（））重新加载我的线程中的顶点时，问题不再发生。当我将顶点对象引用传递给我的线程并在那里使用它时，我得到各种错误。我假设OrientVertex类不是线程安全的。

Answer 1

你是对的所有图元素都不是线程安全的。
创建边缘时出现异常的原因，在图形数据库下面创建文档，其类等于边的标签。如果缺少类，则会自动提交事务，并在模式中创建新类。当您同时添加边缘时，每个类都映射到数据库中的集群（它就像一个表），同时创建相同的类，从而创建相同的集群。因此，一个线程赢得其他失败，除了已经创建了具有给定名称的群集。实际上我建议你在运行时添加边之前创建所有类，也就是边缘标签。

还有一个建议。您应该将OrientGraph实例视为与服务器的连接。最佳用法如下：

OrientGraphFactory中的设置池
在交易前获取图表实例。
执行交易。
致电 .shutdown（），不要创建长实时图表实例。

Java中的OrientDB并发图操作

1 个答案: