SUBQUERIES IN DISTRIBUTED ASYNCHRONOUS GRAPH QUERIES

A graph processing engine is provided for executing a graph query comprising a parent query and a subquery nested within the parent query. The subquery is an existential subquery, uses a reference to one or more correlated variables from the parent query, is inlined in the parent query pattern matching, does not have a post-processing phase, does not contain any global aggregation operations, uses a reference to at most one non-correlated variable, and does not include any filters on a non-correlated variable. Executing the graph query comprises initiating execution of the parent query, responsive to the parent query matching the one or more correlated variables in an intermediate result set, executing the subquery by applying a neighbor pattern matching operator that checks for existence of an edge, and resuming execution of the parent query based on results of the neighbor pattern matching operation.