Stephen O'Donnell created HDFS-14624:
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Summary: When decommissioning a node, log remaining blocks to
replicate periodically
Key: HDFS-14624
URL: https://issues.apache.org/jira/browse/HDFS-14624
Project: Hadoop HDFS
Issue Type: Improvement
Components: namenode
Affects Versions: 3.3.0
Reporter: Stephen O'Donnell
Assignee: Stephen O'Donnell
When a node is marked for decommission, there is a monitor thread which runs
every 30 seconds by default, and checks if the node still has pending blocks to
be replicated before the node can complete replication.
There are two existing debug level messages logged in the monitor thread,
DatanodeAdminManager$Monitor.check(), which log the correct information
already, first as the pending blocks are replicated:
{code:java}
LOG.debug("Node {} still has {} blocks to replicate "
+ "before it is a candidate to finish {}.",
dn, blocks.size(), dn.getAdminState());{code}
And then after the initial set of blocks has completed and a rescan happens:
{code:java}
LOG.debug("Node {} {} healthy."
+ " It needs to replicate {} more blocks."
+ " {} is still in progress.", dn,
isHealthy ? "is": "isn't", blocks.size(), dn.getAdminState());{code}
I would like to propose moving these messages to INFO level so it is easier to
monitor decommission progress over time from the Namenode log.
Based on the default settings, this would result in at most 1 log message per
node being decommissioned every 30 seconds. The reason this is at the most, is
because the monitor thread stops after checking after 500K blocks and therefore
in practice it could be as little as 1 log message per 30 seconds, even if many
DNs are being decommissioned at the same time.
Note that the namenode webUI does display the above information, but having
this in the NN logs would allow progress to be tracked more easily.
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