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https://issues.apache.org/jira/browse/GEARPUMP-349?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16166167#comment-16166167
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ASF GitHub Bot commented on GEARPUMP-349:
-----------------------------------------
Github user manuzhang commented on a diff in the pull request:
https://github.com/apache/incubator-gearpump/pull/223#discussion_r138876832
--- Diff: core/src/main/scala/org/apache/gearpump/util/Graph.scala ---
@@ -243,13 +259,34 @@ class Graph[N, E](vertexList: List[N], edgeList:
List[(N, E, N)]) extends Serial
* The node returned by Iterator is stable sorted.
*/
def topologicalOrderIterator: Iterator[N] = {
- val newGraph = copy
- var output = List.empty[N]
-
- while (!newGraph.isEmpty) {
- output ++= newGraph.removeZeroInDegree
+ tryTopologicalOrderIterator.get
+ }
+
+ private def tryTopologicalOrderIterator: Try[Iterator[N]] = {
+ Try {
+ val indegreeMap = mutable.Map.empty[N, Int]
--- End diff --
why not generate `indegreeMap` with `vertices.map` ?
> Graph#topologicalOrderIterator is slow for large graph
> ------------------------------------------------------
>
> Key: GEARPUMP-349
> URL: https://issues.apache.org/jira/browse/GEARPUMP-349
> Project: Apache Gearpump
> Issue Type: Improvement
> Components: core
> Affects Versions: 0.8.4
> Reporter: Manu Zhang
> Assignee: Huafeng Wang
> Fix For: 0.8.5
>
>
> The algorithm is as follows
> 1. find zero in-degree nodes from a copied graph.
> 2. remove nodes from the copied graph and add them to the output
> 3. repeat 1
> The issue is that step 1 traverses all remaining nodes each time, which costs
> the algorithm {{O(n^2)}} time
> {{Graph#hasCycle}} has a similar issue
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