gnodet opened a new pull request, #2153:
URL: https://github.com/apache/maven-resolver/pull/2153
## Problem
`PathConflictResolver` runs out of memory (`OutOfMemoryError: Java heap
space`) on highly connected dependency graphs, such as a 813-module reactor
where each module depends on ~9 others.
Reproduced with `-Xmx512m`:
```
java.lang.OutOfMemoryError: Java heap space
at PathConflictResolver$Path.addChildren(PathConflictResolver.java:699)
at
PathConflictResolver$State.gatherCRNodes(PathConflictResolver.java:363)
```
Workaround: `-Daether.conflictResolver.impl=classic`
## Root Cause
`gatherCRNodes` performs a BFS/DFS traversal that creates a new `Path`
object for **every edge** in the expanded dependency tree — not just one per
`DependencyNode`. When the same node is reachable via N different parent paths,
its entire subtree is traversed N times, leading to exponential `Path`
allocation.
For 813 modules × ~9 avg deps, this produces millions of `Path` objects
instead of the ~7,500 that actually represent unique graph edges.
## Fix
Two complementary changes:
**1. Expansion deduplication** (the OOM fix):
Track which `DependencyNode` instances have already been expanded in an
`IdentityHashMap<DependencyNode, Integer>` (mapped to expansion depth). When
the same `DependencyNode` is encountered again via a different parent path, a
`Path` entry is still created for it (so all occurrences appear in the conflict
partition for winner selection), but its subtree is **not re-traversed**. If
the same node is later reached at a shallower depth, it is re-expanded and the
recorded minimum is updated.
**2. Remove per-Path `HashSet` copy** (CPU/memory fix):
The `HashSet<String> conflictIdsOnPath` that was copied on every `Path`
construction is dropped. Since expansion deduplication already bounds total
path count to O(graph edges), the O(depth) parent-chain walk for
`hasConflictIdOnPathToRoot` is sufficient and cheaper. This also eliminates the
per-node allocation that was identified as a JFR hotspot in the prior PR #2075.
## Testing
- All 452 existing `maven-resolver-util` tests pass
- The 813-module reproducer that previously OOMed with 512m heap now
completes in ~20s
- Both `path` and `classic` resolvers produce identical results on the
reproducer
_Hermes Agent (Claude Sonnet 4.6) on behalf of Guillaume Nodet_
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