hgromer opened a new pull request, #7354:
URL: https://github.com/apache/hbase/pull/7354
We started seeing errors when doing incremental backups
```
2025-09-29 19:31:19.527 [main] INFO org.apache.hadoop.mapreduce.Job - Task
Id : attempt_1759167518321_0143_m_000000_0, Status : FAILED
Error: java.lang.IllegalArgumentException: Can't read partitions file
at
org.apache.hadoop.mapreduce.lib.partition.TotalOrderPartitioner.setConf(TotalOrderPartitioner.java:117)
at
org.apache.hadoop.util.ReflectionUtils.setConf(ReflectionUtils.java:79)
at
org.apache.hadoop.util.ReflectionUtils.newInstance(ReflectionUtils.java:140)
at
org.apache.hadoop.mapred.MapTask$NewOutputCollector.<init>(MapTask.java:715)
at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:783)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:348)
at org.apache.hadoop.mapred.YarnChild$2.run(YarnChild.java:178)
at
java.base/java.security.AccessController.doPrivileged(AccessController.java:714)
at java.base/javax.security.auth.Subject.doAs(Subject.java:525)
at
org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1899)
at org.apache.hadoop.mapred.YarnChild.main(YarnChild.java:172)
Caused by: java.io.IOException: Wrong number of partitions in keyset
at
org.apache.hadoop.mapreduce.lib.partition.TotalOrderPartitioner.setConf(TotalOrderPartitioner.java:91)
... 10 more
```
The root cause is that the SnapshotRegionLocator which is used as the
RegionLocator for modern backups can return dupe start keys in the case of
region splits.
`HFileOutputFormat2` will do two things
1. Configure the number of reducers based on the # of start keys that we get
from _all_ region locations
2. De-dupe the start keys and write the partitions based on the de-duped set
When this happens, the TotalOrderPartitioner fails because it's expecting
the same number of reducers are partitions.
We should filter out regions that are either offline, or have been split,
which is the same thing that the
[MetaTableAccessor](https://github.com/HubSpot/hbase/blob/70f6120227f9050c8b3cb7c6bb33a768264cf5c4/hbase-client/src/main/java/org/apache/hadoop/hbase/MetaTableAccessor.java#L1261C13-L1261C19)
does.
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