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https://issues.apache.org/jira/browse/CALCITE-4049?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17134931#comment-17134931
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Xiening Dai commented on CALCITE-4049:
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Based on the usage pattern, I don't think the shortest path is even needed.
What we need is -
1. A fast way to detect the accessibility between two vertexes.
2. Method to get all path between two vertexes.
For #1, we can build and cache an accessibility matrix when frozen the graph.
And #2 can be calculated on-demand using DFS, since it's not at a hot path.
> Reduce the time complexity of getting shortest distances
> --------------------------------------------------------
>
> Key: CALCITE-4049
> URL: https://issues.apache.org/jira/browse/CALCITE-4049
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Reporter: Liya Fan
> Assignee: Liya Fan
> Priority: Major
> Fix For: 1.24.0
>
> Time Spent: 1h 20m
> Remaining Estimate: 0h
>
> Currently, we have {{Graphs#makeImmutable}} to compute the shortest paths
> between all pairs of nodes. For many scenarios, however, we do not need the
> exact paths between nodes. Instead, we are only interested in the lengths of
> the shortest paths.
> To get the path length, we need to get the shortest path first, which is
> returned as a {{List}}, then we call the {{List#size()}} method. According to
> the current implementation, the returned list is of type {{ConsList}}. The
> time complexity of {{ConsList#size}} is O(p) (p is the number of vertices on
> the path), which is inefficient.
> In this issue, we revise the implementation of {{ConsList#size}} so that it
> takes O(1) time. In addition, we also give a utiltiy to get the shortest
> distances between nodes.
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