FAQ

• How to choose the back-end storage? Choose RocksDB or Cassandra or Hbase or Mysql?

  Judge according to your specific needs. Generally, if the stand-alone machine or the data volume is < 10 billion, RocksDB is recommended, and other back-end clusters that use distributed storage are recommended.

• Prompt when starting the service: xxx (core dumped) xxx

  Please check if the JDK version is Java 11, at least Java 8 is required

• The service is started successfully, but there is a prompt similar to “Unable to connect to the backend or the connection is not open” when operating the graph

  init-storeBefore starting the service for the first time, you need to use the initialization backend first , and subsequent versions will prompt more clearly and directly.

• Do all backends need to be executed before use init-store, and can the serialization options be filled in at will?

  Except memorynot required, other backends are required, such as: cassandra, hbaseand, rocksdb, etc. Serialization needs to be one-to-one correspondence and cannot be filled in at will.

• Execution init-store error: Exception in thread "main" java.lang.UnsatisfiedLinkError: /tmp/librocksdbjni3226083071221514754.so: /usr/lib64/libstdc++.so.6: version `GLIBCXX_3.4.10' not found (required by /tmp/librocksdbjni3226083071221514754.so)

  RocksDB requires gcc 4.3.0 (GLIBCXX_3.4.10) and above

• The error NoHostAvailableException occurred while executing init-store.sh.

  NoHostAvailableException means that the Cassandra service cannot be connected to. If you are sure that you want to use the Cassandra backend, please install and start this service first. As for the message itself, it may not be clear enough, and we will update the documentation to provide further explanation.

• The bin directory contains start-hugegraph.sh, start-restserver.sh and start-gremlinserver.sh. These scripts seem to be related to startup. Which one should be used?

  Since version 0.3.3, GremlinServer and RestServer have been merged into HugeGraphServer. To start, use start-hugegraph.sh. The latter two will be removed in future versions.

• Two graphs are configured, the names are hugegraph and hugegraph1, and the command to start the service is start-hugegraph.sh. Is only the hugegraph graph opened?

  start-hugegraph.sh will open all graphs under the graphs of gremlin-server.yaml. The two have no direct relationship in name

• After the service starts successfully, garbled characters are returned when using curl to query all vertices

  The batch vertices/edges returned by the server are compressed (gzip), and can be redirected to gunzip for decompression (curl http://example | gunzip), or can be sent with the postman of Firefox or the restlet plug-in of Chrome browser. request, the response data will be decompressed automatically.

• When using the vertex Id to query the vertex through the RESTful API, it returns empty, but the vertex does exist

  Check the type of the vertex ID. If it is a string type, the “id” part of the API URL needs to be enclosed in double quotes, while for numeric types, it is not necessary to enclose the ID in quotes.

• Vertex Id has been double quoted as required, but querying the vertex via the RESTful API still returns empty

  Check whether the vertex id contains +, space, /, ?, %, &, and = reserved characters of these URLs. If they exist, they need to be encoded. The following table gives the coded values:

  special character | encoded value
  ------------------| -------------
  +                 | %2B
  space             | %20
  /                 | %2F
  ?                 | %3F
  %                 | %25
  #                 | %23
  &                 | %26
  =                 | %3D

• Timeout when querying vertices or edges of a certain category (query by label)

  Since the amount of data belonging to a certain label may be relatively large, please add a limit limit.

• It is possible to operate the graph through the RESTful API, but when sending Gremlin statements, an error is reported: Request Failed(500)

  It may be that the configuration of GremlinServer is wrong, check whether the host and port of gremlin-server.yaml match the gremlinserver.url of rest-server.properties, if they do not match, modify them, and then Restart the service.

• When using Loader to import data, a Socket Timeout exception occurs, and then Loader is interrupted

  Continuously importing data will put too much pressure on the Server, which will cause some requests to time out. The pressure on Server can be appropriately relieved by adjusting the parameters of Loader (such as: number of retries, retry interval, error tolerance, etc.), and reduce the frequency of this problem.

• How to delete all vertices and edges. There is no such interface in the RESTful API. Calling g.V().drop() of gremlin will report an error Vertices in transaction have reached capacity xxx

  At present, there is really no good way to delete all the data. If the user deploys the Server and the backend by himself, he can directly clear the database and restart the Server. You can use the paging API or scan API to get all the data first, and then delete them one by one.

• The database has been cleared and init-store has been executed, but when trying to add a schema, the prompt “xxx has existed” appeared.

  There is a cache in the HugeGraphServer, and it is necessary to restart the Server when the database is cleared, otherwise the residual cache will be inconsistent.

• An error is reported during the process of inserting vertices or edges: Id max length is 128, but got xxx {yyy} or Big id max length is 32768, but got xxx

  In order to ensure query performance, the current backend storage limits the length of the id column. The vertex id cannot exceed 128 bytes, the edge id cannot exceed 32768 bytes, and the index id cannot exceed 128 bytes.

• Is there support for nested attributes, and if not, are there any alternatives?

  Nested attributes are currently not supported. Alternative: Nested attributes can be taken out as individual vertices and connected with edges.

• Can an EdgeLabel connect multiple pairs of VertexLabel, such as “investment” relationship, which can be “individual” investing in “enterprise”, or “enterprise” investing in “enterprise”?

  An EdgeLabel does not support connecting multiple pairs of VertexLabels, users need to split the EdgeLabel into finer details, such as: “personal investment”, “enterprise investment”.

• Prompt HTTP 415 Unsupported Media Type when sending a request through RestAPI

  Content-Type: application/json needs to be specified in the request header

Other issues can be searched in the issue area of the corresponding project, such as Server-Issues / Loader Issues

Last modified May 14, 2023: Update faq.md (#223) (ecb96905)