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  1. Calcite
  2. CALCITE-3827

Reduce the time complexity of finding in-edges of a vertex in the graph

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Details

    • Improvement
    • Status: Closed
    • Major
    • Resolution: Fixed
    • None
    • 1.23.0
    • core

    Description

      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 (e.g. topological sort).

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              julianhyde Julian Hyde
              fan_li_ya Liya Fan
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