Can't get management instance of graph - gremlin

Question

I connect to gremlin server from gremlin console:
:remote connect tinkerpop.server config/connect_config.yaml
I can execute queries like:
:> graph.getGraphName()
:> g.V().count().next()
:> g.V().drop().iterate()
:> g.V().values('LOL')
and many others. g - GraphTraversalSource, graph - StandardJanusGraph.
I need to configure schema of graph:
:> mg = graph.openManagenet()
but when i try to execute this query, i get exception:
gremlin> :> mngmt = graph.openManagement()
Server could not serialize the result requested. Server error - Error during serialization: Class is not registered: org.janusgraph.graphdb.database.management.ManagementSystem
Note: To register this class use: kryo.register(org.janusgraph.graphdb.database.management.ManagementSystem.class);. Note that the class must be serializable by the client and server for proper operation.
Type ':help' or ':h' for help.
Display stack trace? [yN]y
org.apache.tinkerpop.gremlin.groovy.plugin.RemoteException: Server could not serialize the result requested. Server error - Error during serialization: Class is not registered: org.janusgraph.graphdb.database.management.ManagementSystem
Note: To register this class use: kryo.register(org.janusgraph.graphdb.database.management.ManagementSystem.class);. Note that the class must be serializable by the client and server for proper operation.
at org.apache.tinkerpop.gremlin.console.groovy.plugin.DriverRemoteAcceptor.submit(DriverRemoteAcceptor.java:186)
at org.apache.tinkerpop.gremlin.console.commands.SubmitCommand.execute(SubmitCommand.groovy:41)
at org.codehaus.groovy.tools.shell.Shell.execute(Shell.groovy:104)
at org.codehaus.groovy.tools.shell.Groovysh.super$2$execute(Groovysh.groovy)
at sun.reflect.GeneratedMethodAccessor15.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:98)
at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1225)
at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.invokeMethodOnSuperN(ScriptBytecodeAdapter.java:145)
at org.codehaus.groovy.tools.shell.Groovysh.executeCommand(Groovysh.groovy:273)
at org.codehaus.groovy.tools.shell.Groovysh.execute(Groovysh.groovy:164)
at org.apache.tinkerpop.gremlin.console.GremlinGroovysh.super$3$execute(GremlinGroovysh.groovy)
at sun.reflect.GeneratedMethodAccessor14.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:98)
at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1225)
at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.invokeMethodOnSuperN(ScriptBytecodeAdapter.java:145)
at org.apache.tinkerpop.gremlin.console.GremlinGroovysh.execute(GremlinGroovysh.groovy:72)
at org.codehaus.groovy.tools.shell.Shell.leftShift(Shell.groovy:122)
at org.codehaus.groovy.tools.shell.ShellRunner.work(ShellRunner.groovy:95)
at org.codehaus.groovy.tools.shell.InteractiveShellRunner.super$2$work(InteractiveShellRunner.groovy)
at sun.reflect.GeneratedMethodAccessor35.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:98)
at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1225)
at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.invokeMethodOnSuperN(ScriptBytecodeAdapter.java:145)
at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.invokeMethodOnSuper0(ScriptBytecodeAdapter.java:165)
at org.codehaus.groovy.tools.shell.InteractiveShellRunner.work(InteractiveShellRunner.groovy:130)
at org.codehaus.groovy.tools.shell.ShellRunner.run(ShellRunner.groovy:59)
at org.codehaus.groovy.tools.shell.InteractiveShellRunner.super$2$run(InteractiveShellRunner.groovy)
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.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:98)
at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1225)
at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.invokeMethodOnSuperN(ScriptBytecodeAdapter.java:145)
at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.invokeMethodOnSuper0(ScriptBytecodeAdapter.java:165)
at org.codehaus.groovy.tools.shell.InteractiveShellRunner.run(InteractiveShellRunner.groovy:89)
at org.codehaus.groovy.vmplugin.v7.IndyInterface.selectMethod(IndyInterface.java:236)
at org.apache.tinkerpop.gremlin.console.Console.<init>(Console.groovy:169)
at org.codehaus.groovy.vmplugin.v7.IndyInterface.selectMethod(IndyInterface.java:236)
at org.apache.tinkerpop.gremlin.console.Console.main(Console.groovy:481)
Can somebody say me what i must do to fix this problem?

Answer 1

I'm not sure that the ManagementSystem is serializable so that's why you are getting that error. There are at least two ways to sort it out. First, you didn't post what is in your config/connect_config.yaml but I assume it is not using this sort of configuration option for the serializer:
hosts: [localhost]
port: 8182
serializer: { className: org.apache.tinkerpop.gremlin.driver.ser.GryoMessageSerializerV3d0, config: { serializeResultToString: true }}
By using the serializeResultToString option (and assuming that serializer is configured in Gremlin Server in its configuration) you tell Gremlin Server to take any result you get and call toString() on it before it is returned. In that way, you never get serialization errors.
But, the downside is that you only get String values back. Generally speaking, I would think that is ok for most Gremlin Console interactions (especially administrative ones like the one you are trying to execute with the ManagementSystem API. So, if you wanted to continue using your current configuration which tries to serialize actual "objects" you just need to be sure your scripts only return data that is serializable so instead of:
:> mg = graph.openManagement()
do
:> mg = graph.openManagement();[]
which doesn't return mg, but rather an empty list.