Graph Database Systems (GDBs) support efficiently storing and retrieving graph data, and have become a critical component in many important applications. Many widely-used GDBs utilize the Gremlin query language to create, modify, and retrieve data in graph databases, in which developers can assemble a sequence of Gremlin APIs to perform a complex query. However, incorrect implementations and optimizations of GDBs can introduce logic bugs, which can cause Gremlin queries to return incorrect query results, e.g., omitting vertices in a graph database.

In this paper, we propose Query Di sassembling (QuDi), an effective testing technique to automatically detect logic bugs in Gremlin-based GDBs. Given a Gremlin query Q, QuDi disassembles Q into a sequence of atomic graph traversals TList, which shares the equivalent execution semantics with Q. If the execution results of Q and TList are different, a logic bug is revealed in the target GDB. We evaluate QuDi on six popular GDBs, and have found 25 logic bugs in these GDBs, 10 of which have been confirmed as previously-unknown bugs by GDB developers.