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https://issues.apache.org/jira/browse/HDFS-12977?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16402512#comment-16402512
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Chen Liang commented on HDFS-12977:
-----------------------------------
Thanks [~zero45] for working on this! patch looks pretty good to me. Just one
minor thing, looks {{ClientGCIContext#receiveResponseState}} will be called on
every single client RPC. Since there can be high volume of such calls, I think
it might worth considering to minimize the synchronization overhead here.
Instead of using synchronized, maybe we can leverage Java 8's
[{{LongAccumulator}}|https://docs.oracle.com/javase/8/docs/api/java/util/concurrent/atomic/LongAccumulator.html],
such as:
{code}
LongAccumulator longAccumulator = new LongAccumulator(Long::max,
Long.MIN_VALUE);
{code}
Then in receiveResponseState, it's just:
{code}
long lastSeenStateId = header.getStateId();
lastSeenStateId.accumulate(lastSeenStateId);
{code}
> Add stateId to RPC headers.
> ---------------------------
>
> Key: HDFS-12977
> URL: https://issues.apache.org/jira/browse/HDFS-12977
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: ipc, namenode
> Reporter: Konstantin Shvachko
> Assignee: Plamen Jeliazkov
> Priority: Major
> Attachments: HDFS_12977.trunk.001.patch, HDFS_12977.trunk.002.patch,
> HDFS_12977.trunk.003.patch, HDFS_12977.trunk.004.patch,
> HDFS_12977.trunk.005.patch, HDFS_12977.trunk.006.patch,
> HDFS_12977.trunk.007.patch
>
>
> stateId is a new field in the RPC headers of NameNode proto calls.
> stateId is the journal transaction Id, which represents LastSeenId for the
> clients and LastWrittenId for NameNodes. See more in [reads from Standby
> design
> doc|https://issues.apache.org/jira/secure/attachment/12902925/ConsistentReadsFromStandbyNode.pdf].
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