Stephen O'Donnell created HDDS-8074:
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Summary: Improve synchronization around command queue updates in
Node Manager
Key: HDDS-8074
URL: https://issues.apache.org/jira/browse/HDDS-8074
Project: Apache Ozone
Issue Type: Sub-task
Components: SCM
Reporter: Stephen O'Donnell
Assignee: Stephen O'Donnell
The total commands pending for a datanode is the sum of the commands on the
NodeManager CommandQueue and the number of commands the DN reported it has in
the previous heartbeat.
As things stand, these two piece of information come from two different
methods, each with their own locking, the result is potentially inconsistent.
To allow a consistent view of the commands queued on a data, this PR:
1. Adds a read write lock into the SCMNodeManager so it can lock around updates
to the command queue, updating the DN queue count in heartbeat processing and
querying the counts.
2. Moves the CommandQueueReportProcessing from being asynchronous to being
processed as part of the heartbeat in SCM. This avoids a problem were the
command queue has been emptied, but the pending count has not been updated
inside DatanodeInfo.
3. In an earlier PR, a low priority flag was added to ReplicateContainer
commands, so that the balancer can send commands with a lower priority. The DN
does not report these low priority commands in its counts, so the command queue
has been adjusted to not count them either.
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