kokonguyen191 commented on code in PR #6861:
URL: https://github.com/apache/hadoop/pull/6861#discussion_r1636165686
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hadoop-hdfs-project/hadoop-hdfs-rbf/src/site/markdown/HDFSRouterFederation.md:
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@@ -288,6 +288,7 @@ For deciding where to create a new file/folder it uses the
order parameter, it c
* RANDOM: Random subcluster. This is usually useful for balancing the load
across. Folders are created in all subclusters.
* HASH_ALL: Follow consistent hashing at all the levels. This approach tries
to balance the reads and writes evenly across subclusters. Folders are created
in all subclusters.
* SPACE: Try to write data in the subcluster with the most available space.
Folders are created in all subclusters.
+* LEADER_FOLLOWER: Try to write data in the leader sub-cluster as many as
possible, if failed, try follower sub-clusters then. Folders are created in all
sub-clusters.
Review Comment:
`Try to write data in the leader subcluster as much as possible, if failed,
try follower subclusters. Folders are created in all subclusters.`
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hadoop-hdfs-project/hadoop-hdfs-rbf/src/site/markdown/HDFSRouterFederation.md:
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@@ -297,6 +298,9 @@ RANDOM can be used for reading and writing data from/into
different subclusters.
The common use for this approach is to have the same data in multiple
subclusters and balance the reads across subclusters.
For example, if thousands of containers need to read the same data (e.g., a
library), one can use RANDOM to read the data from any of the subclusters.
+LEADER_FOLLOWER can be used in cross-cluster disaster tolerance, it's not for
sharing overloads among sub-clusters. When using this mode like `-add /data
ns2,ns1 /data -order LEADER_FOLLOWER`,
+`ns2` is considered as a active sub-cluster and `ns1` is considered as a
follower sub-cluster. The order of namespaces is always
`leader,follower,follower...`
Review Comment:
```
`ns2` is considered an active subcluster and `ns1` is considered a follower
subcluster. The order of namespaces is always `leader,follower,follower...`.
```
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hadoop-hdfs-project/hadoop-hdfs-rbf/src/main/java/org/apache/hadoop/hdfs/server/federation/resolver/order/DestinationOrder.java:
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@@ -29,11 +29,14 @@ public enum DestinationOrder {
LOCAL, // Local first
RANDOM, // Random order
HASH_ALL, // Follow consistent hashing
- SPACE; // Available space based order
+ SPACE, // Available space based order
+ LEADER_FOLLOWER; // try leader sub-cluster first, if failed, try followers
Review Comment:
Small nitpick but should capitalize the first letter of the comment to keep
it consistent with the other comments
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