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From "Colin P. McCabe" <cmcc...@apache.org>
Subject state of the htrace
Date Wed, 27 Jan 2016 21:17:34 GMT
Hi all,

Happy (belated) New Year.  I've been a bit quiet since I went on
vacation for a few weeks recently, and since I have some other
projects going on.  But today I wanted to highlight some really cool
stuff that's been happening in the HTrace and broader tracing
community recently.

Last weekend, I gave an "intro to htrace" talk this weekend at the
Scale 14x Linux conference.  See
https://www.socallinuxexpo.org/scale/14x/presentations/introducing-apache-htrace
.  Also there is a video here:
https://www.youtube.com/watch?v=t-TwCLwYIGE  It starts at 6:50, since
the first few minutes of the recording are just me setting up the VGA
connection and microphone :P  I thought this one went really well
(especially the demo), and hopefully will get the word out to even
more people.

In HDFS, we've been exploring adding annotations to certain trace
spans to collect even more useful information.  For example, Zhe Zhang
posted a patch to HDFS-9576 to add "position" and "length" annotations
to DFSInputStream#byteArrayRead, etc. spans.  This should give us data
on things like the average and median read length in a set of HDFS
requests.  Similarly, I posted HDFS-9674 which adds the "maximum write
latency" to OpWriteBlock spans generated by the DataNode.  This is
very handy when analyzing HDFS write pipelines.  I think we will see
more of these really helpful annotations, and they will expand our
ideas about what HTrace can do.

A few weeks back, I wrote a blog post for my employer, Cloudera.  It
talks about setting up HTrace and htraced on a CDH5.5 cluster.  See
http://blog.cloudera.com/blog/2015/12/new-in-cloudera-labs-apache-htrace-incubating/
 Hopefully HTrace can "bridge the chasm" between being a developer
tool, and being a trusted ops tool.  We have some ways to go, but
having these precompiled packages for CDH5.5 is a big step forward.
(OK, I'll shut up about vendor stuff now...)

Another really cool thing is that Sean Busbey and others in the YCSB
community are working on integrating HTrace.  YCSB is a very popular
benchmark for big data / Hadoopy workloads.  The github issue is here:
https://github.com/brianfrankcooper/YCSB/issues/415

cheers,
Colin

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