Uma Maheswara Rao G created HDDS-12864:
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Summary: All commit semantics in replication writes
Key: HDDS-12864
URL: https://issues.apache.org/jira/browse/HDDS-12864
Project: Apache Ozone
Issue Type: New Feature
Components: Ozone Client, Ozone Datanode
Reporter: Uma Maheswara Rao G
Assignee: Swaminathan Balachandran
In Ozone replication(Raft based) has the semantics of majority commit. While
this has the advantage of not suffering from a slow node, this will allow the
system to move forward with majority replication for a short duration of time
without having to have all 3 replicas consistently committed. Catching a slow
replica is dependent on a raft.
Since Ozone has a variable length of blocks, it is just fine to close the
container/block when some of the replicas are not acknowledged in time. So, it
does need to recopy the content to new nodes, instead, it can just move forward
with a new pipeline.
With this advantage, we should provide all commit semantics to make sure all
replicas are consistently committed to a length that the client got
acknowledgments for.
There are two/three areas where we do the majority of commits today:
1. Client falls back to the majority commits in watchForCommit if all commits
fail.
2. Leader DN always waits for the majority quorum for transactions
3. The leader only waits for self applyTransaction completion.
Making the above scenarios streamlines and achieving all commits can bring all
replicas into a consistent state at any point in time, on write acks.
As a side note: Today, in EC, we already do ALL COMMIT like protocol in write
path. Which avoids QUASI_CLOSED state altogether as replicas always have at the
minimum length of data, as it is acknowledged to the clients.
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