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From "Colin Patrick McCabe (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-7189) Add trace spans for DFSClient metadata operations
Date Thu, 15 Jan 2015 20:14:35 GMT

    [ https://issues.apache.org/jira/browse/HDFS-7189?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14279238#comment-14279238

Colin Patrick McCabe commented on HDFS-7189:

bq. But I think the spans \[for queryDatanodeForHdfsBlocksMetadata comments\] should be in
the same trace tree and as a child span instead of start a new trace. So we should pass the
trace info (trace id parent span id) to continue span.

Good idea.  That way, if a {{DFSClient#getBlockStorageLocations}} call takes a long time,
the trace might be helpful to show which datanode is lagging.

bq. Some DFSClient operations don't have trace spans, should we add them?

The operations that I didn't add tracing for broke down into two categories:
* Things that we're going to do later in the "add tracing to DFSOutputStream" change (this
is why callAppend isn't traced, append, connectToDN, etc.)
* Things that look like they're not very time-consuming.  Like getCryptoProtocolVersion which
just fetches the version out of a FileEncryptionInfo object.

Actually, though, I do see one or two things where I should add tracing, like getStoragePolicies.
 Let me add those.

We can always add tracing to stuff later, so I don't think this should be a blocker for this
going in.  And we will certainly adjust the trace points later based on what we learn... to
put more in some places and fewer in others.  But thanks for getting me thinking about this.

bq. Typo? It should be "dst"

Argh.  Thanks

bq. In getSrcDstTraceScope, we'd better check dst != null too.


> Add trace spans for DFSClient metadata operations
> -------------------------------------------------
>                 Key: HDFS-7189
>                 URL: https://issues.apache.org/jira/browse/HDFS-7189
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: datanode, namenode
>    Affects Versions: 2.7.0
>            Reporter: Colin Patrick McCabe
>            Assignee: Colin Patrick McCabe
>         Attachments: HDFS-7189.001.patch, HDFS-7189.003.patch, HDFS-7189.004.patch, HDFS-7189.005.patch,
> We should add trace spans for DFSClient metadata operations.  For example, {{DFSClient#rename}}
should have a trace span, etc. etc.

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