query method for what kind of safe mode the Namenode is in
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Key: HDFS-1726
URL: https://issues.apache.org/jira/browse/HDFS-1726
Project: Hadoop HDFS
Issue Type: Improvement
Components: name-node
Affects Versions: 0.22.0
Reporter: Matt Foley
Assignee: Matt Foley
Fix For: 0.23.0
If we could differentiate between "startup safemode" vs other safemode, it
would be easier to do startup optimizations like HDFS-1295. Looking at
FSNamesystem, this can be queried, but not with a single query, and the
semantics are not reliable under future changes. Also, the FSNamesystem code
itself, internally, uses more than one way to test for manual safe mode.
Proposal is to create a status field and query method in FSNamesystem with enum
values
{NOT_IN_SAFEMODE, SAFEMODE_STARTUP, SAFEMODE_EXTENSION, SAFEMODE_MANUAL}
If in the future we add automatic fallback to safe mode, we would add value
SAFEMODE_AUTOMATIC.
This change will make it easier to do startup optimizations, and will also
allow making the safemode management code in FSNamesystem simpler and more
consistent.
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