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https://issues.apache.org/jira/browse/CALCITE-3827?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Liya Fan updated CALCITE-3827:
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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).
was:
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).
> 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
> Priority: Major
> Labels: pull-request-available
> Time Spent: 10m
> Remaining Estimate: 0h
>
> 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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