[
https://issues.apache.org/jira/browse/HDFS-13573?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16478801#comment-16478801
]
Zsolt Venczel commented on HDFS-13573:
--------------------------------------
Hi [~linyiqun]!
Thanks for the suggestions!
One question about the sentence you mentioned:
{code:java}
* The replica placement strategy is that if the writer is on a datanode,
* the 1st replica is placed on the local machine otherwise a random datanode
* (By passing the {@link org.apache.hadoop.fs.CreateFlag}#NO_LOCAL_WRITE flag
* the client can request not to put a block replica on the local datanode.
{code}
If I understand you correctly you're suggesting the above to be changed to the
following:
{code:java}
* The replica placement strategy is that if the writer is on a datanode,
* the 1st replica is placed on the local machine by default.
* (By passing the {@link org.apache.hadoop.fs.CreateFlag}#NO_LOCAL_WRITE flag
* the client can request not to put a block replica on the local datanode.
{code}
I would suggest not to leave out the scenario when the writer is not on a
datanode and have the following:
{code:java}
* The replica placement strategy is that if the writer is on a datanode,
* the 1st replica is placed on the local machine by default
* (By passing the {@link org.apache.hadoop.fs.CreateFlag#NO_LOCAL_WRITE} flag
* the client can request not to put a block replica on the local datanode.
* Subsequent replicas will still follow default block placement policy.).
* If the writer is not on a datanode, the 1st replica is placed on a random
node.{code}
What do you think?
Best regards,
Zsolt
> Javadoc for BlockPlacementPolicyDefault is inaccurate
> -----------------------------------------------------
>
> Key: HDFS-13573
> URL: https://issues.apache.org/jira/browse/HDFS-13573
> Project: Hadoop HDFS
> Issue Type: Bug
> Affects Versions: 3.1.0
> Reporter: Yiqun Lin
> Assignee: Zsolt Venczel
> Priority: Trivial
> Attachments: HDFS-13573.01.patch
>
>
> Current rule of default block placement policy:
> {quote}The replica placement strategy is that if the writer is on a datanode,
> the 1st replica is placed on the local machine,
> otherwise a random datanode. The 2nd replica is placed on a datanode
> that is on a different rack. The 3rd replica is placed on a datanode
> which is on a different node of the rack as the second replica.
> {quote}
> *if the writer is on a datanode, the 1st replica is placed on the local
> machine*, actually this can be decided by the hdfs client. The client can
> pass {{CreateFlag#NO_LOCAL_WRITE}} that request to not put a block replica on
> the local datanode. But subsequent replicas will still follow default block
> placement policy.
--
This message was sent by Atlassian JIRA
(v7.6.3#76005)
---------------------------------------------------------------------
To unsubscribe, e-mail: hdfs-issues-unsubscr...@hadoop.apache.org
For additional commands, e-mail: hdfs-issues-h...@hadoop.apache.org
