[
https://issues.apache.org/jira/browse/HDFS-11583?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15950328#comment-15950328
]
Masatake Iwasaki commented on HDFS-11583:
-----------------------------------------
[~karanmehta93] , the test code of PHOENIX-3752 uses API of
htrace-3.1.0-incubating.
Since API of htrace-4 is imcompatible with htrace-3, you can not do end-to-end
tracing through hbase-1 and hdfs (of hadoop-2.7). hadoop-2.7 depends on
htrace-4 while hbase-1 depend on htrace-3. Starting tracing spans of htrace-3
does not affect hdfs of hadoop-2.7.
If you could not get expected tracing spans in the test of PHOENIX-3752, the
cause should not be in hdfs.
> Parent spans not initialized to NullScope for every DFSPacket
> -------------------------------------------------------------
>
> Key: HDFS-11583
> URL: https://issues.apache.org/jira/browse/HDFS-11583
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: tracing
> Reporter: Karan Mehta
>
> The issue was found while working with PHOENIX-3752.
> Each packet received by the {{run()}} method of {{DataStreamer}} class, uses
> the {{parents}} field of the {{DFSPacket}} to create a new {{dataStreamer}}
> span, which in turn creates a {{writeTo}} span as its child span. The parents
> field is initialized when the packet is added to the {{dataQueue}} and the
> value is initialized from the {{ThreadLocal}}. This is how HTrace handles
> spans.
> A {{TraceScope}} is created and initialized to {{NullScope}} before the loop
> which runs till the point when the stream is closed.
> Consider the following scenario, when the {{dataQueue}} contains multiple
> packets, only the first of which has a tracing enabled. The scope is
> initialized to the {{dataStreamer}} scope and a {{writeTo}} span is created
> as its child, which gets closed once the packet is sent out to a remote
> datanode. Before {{writeTo}} span is started, the {{dataStreamer}} scope is
> detached. So calling the close method on it doesn't do anything at the end of
> loop.
> The second iteration will be using the stale value of the {{scope}} variable
> with a DFSPacket on which tracing is not enabled. This results in generation
> of an orphan {{writeTo}} spans which are being delivered to the
> {{SpanReceiver}} as registered in the TraceFramework. This may result in
> unlimited number of spans being generated and sent out to receiver.
--
This message was sent by Atlassian JIRA
(v6.3.15#6346)
---------------------------------------------------------------------
To unsubscribe, e-mail: hdfs-issues-unsubscr...@hadoop.apache.org
For additional commands, e-mail: hdfs-issues-h...@hadoop.apache.org
