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From Paul Smith <psm...@aconex.com>
Subject Re: Should HTable.put() return a Future?
Date Wed, 07 Apr 2010 00:49:50 GMT
gents, I'm working on something in the background that may certainly help here.

Right now we (Aconex) have open sourced a performance library called Parfait (ASL 2.0 licensed,
see [1]) for Java, which is generic, but initially targetted at writing data out to SGI's
open-sourced Performance Co-Pilot (PCP) compatible format (see [2])

PCP is designed for monitoring WTF goes on in large clusters (see [3], hopefully that's big
enough for you...). It integrates application, OS and hardware metrics together to get a holistic
view of what is going on.  It logs data into archives, allowing one to retrospectively go
over an event and analyse it.  One can build inference rules then to test theories and then
run the rules over archives to look back in time to see if you had similar events.  The rules
can also be used to check live data to trigger things like Nagios alarms.  We use this extensively
at Aconex.  I could not possibly live without it.  Hard data gets to the bottom quickly. 
Looking through all those log4j log lines would do my head in, I tip my hat to you for trying.
 PCP is totally cross platform (Linux, Mac, Windows).

Parfait can poll JMX counters, or counters can be invoked direct.  I'm working on a MetricContext
that exports all HBase and Hadoop JMX counters into Parfait.  The goal is to be able to have
PCP visualize data more effectively for HBase/Hadoop clusters. To give an example of what
sort of visualization I'd love to have for HBase & Hadoop see a simple working pic of
3d visualisation  at [4] below, that's basic, but imagine a 3D vis of all the HBase region
servers showing visualizations of Hbase specific metrics, played back in real time, or retrospectively
at any pace you want.

I originally posted this back to Hadoop back in September (see [5]), but no-one seemed that
interested which is a bit weird.  had planned to make more progress on this but the Mavenization
got in the way.

At any rate, I'd like to further discuss what requirements for analysing these types of problems
you think you need.  The log4j logging is good (great for some types of basic analysis) but
I think we can do better, and I think Parfait & PCP could really help you guys in production
a LOT..

[1] Parfait - http://code.google.com/p/parfait/
[2] PCP - http://oss.sgi.com/projects/pcp/
[3] NASA's SGI Columbia Supercomputer - http://www.nas.nasa.gov/News/Images/Images/AC04-0208-9.jpg

[4] Clusterviz - http://people.apache.org/~psmith/clustervis.png
[5] Original Hadoop mail - http://markmail.org/search/?q=3D%20Cluster%20Performance%20Visualization#query:3D%20Cluster%20Performance%20Visualization+page:1+mid:4t52nnla4snntwow+state:results

On 07/04/2010, at 5:41 AM, Lars George wrote:

> I agree with Jon here, parsing these files especially not having a
> central logging is bad. I tried Splunk and that sort of worked as well
> to quickly scan for exceptions. A problem were multiline stacktraces
> (which they usually all are). They got mixed up when multiple servers
> sent events at the same time. The Splunk data got all garbled then.
> But something like that yeah.
> Maybe with the new Multiput style stuff the WAL is not such a big
> overhead anymore?
> Lars
> On Tue, Apr 6, 2010 at 7:12 PM, Jonathan Gray <jgray@facebook.com> wrote:
>> I like this idea.
>> Putting major cluster events in some form into ZK.  Could be used for jobs as Todd
says.  Can also be used as a cluster history report on web ui and such.  Higher level historian.
>> I'm a fan of anything that moves us away from requiring parsing hundreds or thousands
of lines of logs to see what has happened.
>> JG
>>> -----Original Message-----
>>> From: Todd Lipcon [mailto:todd@cloudera.com]
>>> Sent: Tuesday, April 06, 2010 9:49 AM
>>> To: hbase-dev@hadoop.apache.org
>>> Subject: Re: Should HTable.put() return a Future?
>>> On Tue, Apr 6, 2010 at 9:46 AM, Jean-Daniel Cryans
>>> <jdcryans@apache.org>wrote:
>>>> Yes it is, you will be missing a RS ;)
>>> How do you detect this, though?
>>> It might be useful to add a counter in ZK for region server crashes. If
>>> the
>>> master ever notices that a RS goes down, it increments it. Then we can
>>> check
>>> the before/after for a job and know when we might have lost some data.
>>> -Todd
>>>> General rule when uploading without WAL is if there's a failure, the
>>>> job is screwed and that's the tradeoff for speed.
>>>> J-D
>>>> On Tue, Apr 6, 2010 at 9:36 AM, Todd Lipcon <todd@cloudera.com>
>>> wrote:
>>>>> On Tue, Apr 6, 2010 at 9:31 AM, Jean-Daniel Cryans
>>> <jdcryans@apache.org
>>>>> wrote:
>>>>>> The issue isn't with the write buffer here, it's the WAL. Your
>>> edits
>>>>>> are in the MemStore so as far as your clients can tell, the data
>>> is
>>>>>> all persisted. In this case you would need to know when all the
>>>>>> memstores that contain your data are flushed... Best practice when
>>>>>> turning off WAL is force flushing the tables after the job is
>>> done,
>>>>>> else you can't guarantee durability for the last edits.
>>>>> You still can't guarantee durability for any of the edits, since a
>>>> failure
>>>>> in the middle of your job is undetectable :)
>>>>> -Todd
>>>>>> J-D
>>>>>> On Tue, Apr 6, 2010 at 4:02 AM, Lars George
>>> <lars.george@gmail.com>
>>>> wrote:
>>>>>>> Hi,
>>>>>>> I have an issue where I do bulk import and since WAL is off and
>>> a
>>>>>>> default write buffer used (TableOutputFormat) I am running into
>>>>>>> situations where the MR job completes successfully but not all
>>> data is
>>>>>>> actually restored. The issue seems to be a failure on the RS
>>> side as
>>>>>>> it cannot flush the write buffers because the MR overloads the
>>> cluster
>>>>>>> (usually the .META: hosting RS is the breaking point) or causes
>>> the
>>>>>>> underlying DFS to go slow and that repercussions all the way
>>> to the
>>>>>>> RS's.
>>>>>>> My question is, would it make sense as with any other
>>> asynchronous IO
>>>>>>> to return a Future from the put() that will help checking the
>>> status
>>>>>>> of the actual server side async flush operation? Or am I
>>> misguided
>>>>>>> here? Please advise.
>>>>>>> Lars
>>>>> --
>>>>> Todd Lipcon
>>>>> Software Engineer, Cloudera
>>> --
>>> Todd Lipcon
>>> Software Engineer, Cloudera

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