[jira] [Created] (CALCITE-3827) Reduce the time complexity of finding in-edges of a vertex in the graph

["Liya Fan (Jira)" <ji...@apache.org>]

Liya Fan created CALCITE-3827:
---------------------------------

             Summary: Reduce the time complexity of finding in-edges of a vertex in the graph
                 Key: CALCITE-3827
                 URL: https://issues.apache.org/jira/browse/CALCITE-3827
             Project: Calcite
          Issue Type: Improvement
          Components: core
            Reporter: Liya Fan


In the current graph implementation, it takes O(1) time to find the out-edges of a vertex, but O(e) time (where e is the total number of edges in the graph) to find the in-edges of a vertex. 

In some scenarios (e.g. clearing cache in hep planner), this may have severe performance penalty.  To solve this problem, we add a inward edge table, in addition to the existing outward edge table, to the graph. This helps to reduce the time complexity for finding in-edges to O(1). 

Please note that, there is extra performance overhead for maintaining the in edge table, when adding/deleting vertices to the graph. However, the added overhead only takes O(1) time.

Finally, it should be noted that, some existing operations can benefit from this improvement (topological sort). 



--
This message was sent by Atlassian Jira
(v8.3.4#803005)