fix(kcore): swap sendMsgToSrc/sendMsgToDst column references#802
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SemyonSinchenko merged 2 commits intographframes:mainfrom Mar 4, 2026
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Each directed edge (u,v) was sending u's own kcore back to u and v's
own kcore back to v, so no vertex ever received a neighbour's value.
The algorithm converged immediately after one superstep returning
kcore = degree for all vertices.
Fix: swap Pregel.src <-> Pregel.dst so each endpoint receives the
opposite end's value, matching the Mandal & Hasan (2017) algorithm.
Also:
- Document that the implementation treats the graph as undirected
(total degree + bidirectional message passing per edge); supplying
both (u,v) and (v,u) double-counts and produces wrong results.
- Fix star-graph test: expected center kcore 3 -> 1 (correct textbook
value; no 2-core can form when leaves each have one neighbour).
- Replace chain-graph test: was a copy of the triangle test with the
same cyclic edges; now uses an actual open chain (0->1->2) with the
correct assertion kcore=1 for all vertices and an explanatory comment.
- Tighten medium-graph range assertions to values produced by the
correct algorithm (distinct count >= 3, central vertex >= 3).
- Add triangle-with-tail regression test with exact oracle values
(kcore={1:2,2:2,3:2,4:1,5:1}) that catches the swapped-message bug.
Co-Authored-By: Claude <noreply@anthropic.com>
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SemyonSinchenko
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Mar 4, 2026
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SemyonSinchenko
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LGTM! Thanks a lot @DavidGi!
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@DavidGi running |
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thanks @SemyonSinchenko , i've applied the formatting! |
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Thanks for the contribution, @DavidGi ! |
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Issue 801
Each directed edge (u,v) was sending u's own kcore back to u and v's own kcore back to v, so no vertex ever received a neighbour's value. The algorithm converged immediately after one superstep returning kcore = degree for all vertices.
Fix: swap Pregel.src <-> Pregel.dst so each endpoint receives the opposite end's value, matching the Mandal & Hasan (2017) algorithm.
Also:
Tested with Spark 3.5.x, 4.0.x, 4.1.x, and verified against NetworkX core_number().