XorSum commented on code in PR #8179:
URL: https://github.com/apache/hadoop/pull/8179#discussion_r2689115235
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hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/resolver/MountTableResolver.java:
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@@ -629,14 +629,27 @@ public String getDefaultNamespace() {
private MountTable findDeepest(final String path) {
readLock.lock();
try {
- Entry<String, MountTable> entry = this.tree.floorEntry(path);
- while (entry != null && !isParentEntry(path, entry.getKey())) {
- entry = this.tree.lowerEntry(entry.getKey());
+ Entry<String, MountTable> floorEntry = this.tree.floorEntry(path);
+ if (floorEntry != null && isParentEntry(path, floorEntry.getKey())) {
+ return floorEntry.getValue();
}
Review Comment:
@KeeProMise Thanks for the suggestion to use HashMap! However, I think it's
better to keep using TreeMap for the following two reasons:
1. **Other code depends on TreeMap-specific methods**: There are other
methods (e.g., `getMountPoints`, `getTreeValues`) that use
`TreeMap.subMap(from, to)`, which does not exist in `HashMap`.
2. **Performance trade-offs between TreeMap and HashMap**: The benchmark
results show that HashMap is not always better than TreeMap. Their performance
characteristics differ depending on the use case:
- **TreeMap performs better for the hit case**
- **HashMap performs better for the not hit case**
The benchmark code is available at:
https://gist.github.com/XorSum/c1ed0b37b46eb6f1e6eb103867a9a0f5
Given that mount hits are the common case in production (as you mentioned
"it should hit in most cases"), TreeMap provides better overall performance for
the typical workload.
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