插入顶点时 JanusGraph 中可能出现死锁答案

【问题标题】：Possible deadlock in JanusGraph when upserting Vertex插入顶点时 JanusGraph 中可能出现死锁
【发布时间】：2020-05-25 13:45:37
【问题描述】：

我正在尝试根据this pattern（旧的合并技巧）在目录树中插入表示目录的顶点。 WORK_ENVIRONMENT_ID 和 PATH 属性组合在一个唯一索引中。

如果顶点不存在，它也通过标记为CONTAINS 的Edge 连接到给定的environmentVertex。顶点的DISCOVERED_AT 属性仍然更新。

简化查询：

            final String addedVertexStep = "addedVertex";

            Vertex fileVertex = (Vertex) graph.traversal().V()
                /* ... querying for unique properties */
                .fold()
                .coalesce(__.unfold(),
                        __.addV(VertexLabels.FILE)
                                /* setting unique properties */
                                .as(addedVertexStep)
                                .V(environmentVertex.id())
                                .addE(EdgeLabels.CONTAINS)
                                .to(addedVertexStep)
                                .property(PropertyKeys.WORK_ENVIRONMENT_ID, workEnvironmentId.asUUID())
                                .select(addedVertexStep)
                )
                /* updating properties */
                .next();

完整查询：

            final String addedVertexStep = "addedVertex";

            Vertex fileVertex = (Vertex) graph.traversal().V()
                .hasLabel(VertexLabels.FILE)
                .has(PropertyKeys.WORK_ENVIRONMENT_ID, workEnvironmentId.asUUID())
                .has(PropertyKeys.PATH, fileMetaInformation.fullPath())
                .fold()
                .coalesce(__.unfold(),
                        __.addV(VertexLabels.FILE)
                                .property(PropertyKeys.PATH, fileMetaInformation.fullPath())
                                .property(PropertyKeys.NAME, fileMetaInformation.simpleName())
                                .property(PropertyKeys.WORK_ENVIRONMENT_ID, workEnvironmentId.asUUID())
                                .property(PropertyKeys.PARENT_PATH, fileMetaInformation.directory().path())
                                .property(PropertyKeys.ID, fileMetaInformation.getId().asUUID())
                                .as(addedVertexStep)
                                .V(environmentVertex.id())
                                .addE(EdgeLabels.CONTAINS)
                                .to(addedVertexStep)
                                .property(PropertyKeys.WORK_ENVIRONMENT_ID, workEnvironmentId.asUUID())
                                .select(addedVertexStep)
                )
                .property(PropertyKeys.DISCOVERED_AT, new Date())
                .next();

这会在一个循环中执行数百次，在一个缓存的线程池中，但使用相同的线程事务：

final Graph threadedGraph = graph.tx().createThreadedTx();

查询的设计或执行方式是否有问题导致死锁？我可以重新设计它以防止这种情况吗？这是我遇到的例外情况。

org.janusgraph.core.JanusGraphException: Possible dead lock detected. Waited for transaction lock without success
    at org.janusgraph.graphdb.transaction.lock.ReentrantTransactionLock.lock(ReentrantTransactionLock.java:46) ~[janusgraph-core-0.4.0.jar:?]
    at org.janusgraph.graphdb.transaction.lock.CombinerLock.lock(CombinerLock.java:45) ~[janusgraph-core-0.4.0.jar:?]
    at org.janusgraph.graphdb.transaction.lock.CombinerLock.lock(CombinerLock.java:42) ~[janusgraph-core-0.4.0.jar:?]
    at org.janusgraph.graphdb.transaction.StandardJanusGraphTx.addProperty(StandardJanusGraphTx.java:769) ~[janusgraph-core-0.4.0.jar:?]
    at org.janusgraph.graphdb.transaction.StandardJanusGraphTx.addProperty(StandardJanusGraphTx.java:745) ~[janusgraph-core-0.4.0.jar:?]
    at org.janusgraph.graphdb.vertices.AbstractVertex.property(AbstractVertex.java:152) ~[janusgraph-core-0.4.0.jar:?]
    at org.janusgraph.core.JanusGraphVertex.property(JanusGraphVertex.java:72) ~[janusgraph-core-0.4.0.jar:?]
    at org.janusgraph.graphdb.util.ElementHelper.attachProperties(ElementHelper.java:80) ~[janusgraph-core-0.4.0.jar:?]
    at org.janusgraph.graphdb.tinkerpop.JanusGraphBlueprintsTransaction.addVertex(JanusGraphBlueprintsTransaction.java:122) ~[janusgraph-core-0.4.0.jar:?]
    at org.janusgraph.graphdb.tinkerpop.JanusGraphBlueprintsTransaction.addVertex(JanusGraphBlueprintsTransaction.java:44) ~[janusgraph-core-0.4.0.jar:?]
    at org.apache.tinkerpop.gremlin.process.traversal.step.map.AddVertexStep.map(AddVertexStep.java:81) ~[gremlin-core-3.4.1.jar:3.4.1]
    at org.apache.tinkerpop.gremlin.process.traversal.step.map.AddVertexStep.map(AddVertexStep.java:43) ~[gremlin-core-3.4.1.jar:3.4.1]
    at org.apache.tinkerpop.gremlin.process.traversal.step.map.MapStep.processNextStart(MapStep.java:37) ~[gremlin-core-3.4.1.jar:3.4.1]
    at org.apache.tinkerpop.gremlin.process.traversal.step.util.AbstractStep.hasNext(AbstractStep.java:143) ~[gremlin-core-3.4.1.jar:3.4.1]
    at org.apache.tinkerpop.gremlin.process.traversal.step.util.ExpandableStepIterator.next(ExpandableStepIterator.java:50) ~[gremlin-core-3.4.1.jar:3.4.1]
    at org.apache.tinkerpop.gremlin.process.traversal.step.map.GraphStep.processNextStart(GraphStep.java:158) ~[gremlin-core-3.4.1.jar:3.4.1]
    at org.apache.tinkerpop.gremlin.process.traversal.step.util.AbstractStep.hasNext(AbstractStep.java:143) ~[gremlin-core-3.4.1.jar:3.4.1]
    at org.apache.tinkerpop.gremlin.process.traversal.step.util.ExpandableStepIterator.next(ExpandableStepIterator.java:50) ~[gremlin-core-3.4.1.jar:3.4.1]
    at org.apache.tinkerpop.gremlin.process.traversal.step.map.MapStep.processNextStart(MapStep.java:36) ~[gremlin-core-3.4.1.jar:3.4.1]
    at org.apache.tinkerpop.gremlin.process.traversal.step.util.AbstractStep.hasNext(AbstractStep.java:143) ~[gremlin-core-3.4.1.jar:3.4.1]
    at org.apache.tinkerpop.gremlin.process.traversal.step.util.ExpandableStepIterator.next(ExpandableStepIterator.java:50) ~[gremlin-core-3.4.1.jar:3.4.1]
    at org.apache.tinkerpop.gremlin.process.traversal.step.map.MapStep.processNextStart(MapStep.java:36) ~[gremlin-core-3.4.1.jar:3.4.1]
    at org.apache.tinkerpop.gremlin.process.traversal.step.map.SelectOneStep.processNextStart(SelectOneStep.java:131) ~[gremlin-core-3.4.1.jar:3.4.1]
    at org.apache.tinkerpop.gremlin.process.traversal.step.util.AbstractStep.hasNext(AbstractStep.java:143) ~[gremlin-core-3.4.1.jar:3.4.1]
    at org.apache.tinkerpop.gremlin.process.traversal.util.DefaultTraversal.hasNext(DefaultTraversal.java:192) ~[gremlin-core-3.4.1.jar:3.4.1]
    at org.apache.tinkerpop.gremlin.process.traversal.step.map.CoalesceStep.flatMap(CoalesceStep.java:58) ~[gremlin-core-3.4.1.jar:3.4.1]
    at org.apache.tinkerpop.gremlin.process.traversal.step.map.FlatMapStep.processNextStart(FlatMapStep.java:49) ~[gremlin-core-3.4.1.jar:3.4.1]
    at org.apache.tinkerpop.gremlin.process.traversal.step.util.AbstractStep.hasNext(AbstractStep.java:143) ~[gremlin-core-3.4.1.jar:3.4.1]
    at org.apache.tinkerpop.gremlin.process.traversal.step.util.ExpandableStepIterator.next(ExpandableStepIterator.java:50) ~[gremlin-core-3.4.1.jar:3.4.1]
    at org.apache.tinkerpop.gremlin.process.traversal.step.sideEffect.SideEffectStep.processNextStart(SideEffectStep.java:38) ~[gremlin-core-3.4.1.jar:3.4.1]
    at org.apache.tinkerpop.gremlin.process.traversal.step.util.AbstractStep.next(AbstractStep.java:128) ~[gremlin-core-3.4.1.jar:3.4.1]
    at org.apache.tinkerpop.gremlin.process.traversal.step.util.AbstractStep.next(AbstractStep.java:38) ~[gremlin-core-3.4.1.jar:3.4.1]
    at org.apache.tinkerpop.gremlin.process.traversal.util.DefaultTraversal.next(DefaultTraversal.java:200) ~[gremlin-core-3.4.1.jar:3.4.1]

【问题讨论】：

标签： deadlock gremlin upsert janusgraph

【解决方案1】：

原来这不是死锁，而是锁拥塞，因为我在同一个事务中批量加载了数千个具有唯一性约束的顶点。

为了解决这个问题，我为每个顶点（或上面目录示例中的顶点链）打开了一个新事务，并在更新下一个顶点（链）之前提交了事务。

【讨论】：