Himanshu Vashishtha created HBASE-8741:
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Summary: Mutations on Regions in recovery mode might have same
sequenceIDs
Key: HBASE-8741
URL: https://issues.apache.org/jira/browse/HBASE-8741
Project: HBase
Issue Type: Bug
Components: MTTR
Affects Versions: 0.95.1
Reporter: Himanshu Vashishtha
Assignee: Himanshu Vashishtha
Currently, when opening a region, we find the maximum sequence ID from all its
HFiles and then set the LogSequenceId of the log (in case the later is at a
small value). This works good in recovered.edits case as we are not writing to
the region until we have replayed all of its previous edits.
With distributed log replay, if we want to enable writes while a region is
under recovery, we need to make sure that the logSequenceId > maximum
logSequenceId of the old regionserver. Otherwise, we might have a situation
where new edits have same (or smaller) sequenceIds.
We can store region level information in the WALTrailer, than this scenario
could be avoided by:
a) reading the trailer of the "last completed" file, i.e., last wal file which
has a trailer and,
b) completely reading the last wal file (this file would not have the trailer,
so it needs to be read completely).
In future, if we switch to multi wal file, we could read the trailer for all
completed WAL files, and reading the remaining incomplete files.
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