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From Gary Helmling <ghelml...@gmail.com>
Subject Re: deprecating (old) metrics in favor of metrics2 framework
Date Tue, 10 Jul 2012 20:55:50 GMT
I agree that having a new metrics2 implementation in 0.96 would be
great to see and seems like a natural fit.  I'm 100% for that.  But I
do think that having metrics2 and (deprecated) metrics v1 in the same
release would be very helpful to users making the transition.  So to
me it seems more natural for 0.96 to be that release with both
implementations, since that's where it seems like the metrics2
implementation will land.

Otherwise it seems like we risk introducing the same disruptions that
Hadoop did when metrics2 initially replaced the metrics v1
implementation, instead of living along side.  This did cause us as a
project some trouble until metrics v1 was added back in.  So it would
be unfortunate to repeat the same mistake ourselves.

If there's considerable pain or overhead in having both
implementations live in parallel, maybe it's worth doing a straight
switch over in 0.96.  I haven't looked at the differences enough
myself to know.  But otherwise it seems like an easier migration path
to deprecate v1 in 0.96 and remove the release after.

On Tue, Jul 10, 2012 at 1:35 PM, Ted Yu <yuzhihong@gmail.com> wrote:
> Gary:
> Your comment makes sense.
> Part of this poll originates from the fact that 0.96 is our singularity
> release. RPC, coprocessor, etc have undergone considerable changes.
> Users migrating to 0.96 would have to deal with a lot of updates in their
> codebase.
> It seems to me that doing all upgrades in one shot is almost the same as
> upgrading components other than metrics framework.
> Cheers
> On Tue, Jul 10, 2012 at 1:29 PM, Gary Helmling <ghelmling@gmail.com> wrote:
>> >
>> > Whether we support 2 (actually more than 2) metrics frameworks in 0.96
>> can
>> > be debated in the next 2 months.
>> >
>> I'm not sure I agree that deprecating without having something in
>> place for users to move to makes sense.
>> > As Todd mentioned in the thread 'HBase 0.94.1', we will try our best to
>> > keep JMX interface the same across 0.94 and 0.96. Does this somehow
>> reduce
>> > the concern you raised ?
>> >
>> I think that maintaining consistency with the existing JMX naming
>> conventions (to the extent possible) is important for operational
>> concerns, but it's independent of the MetricsContext question and the
>> question of whether other metrics classes of our own need a proper
>> deprecation cycle.
>> > As for using MetricsContext, I assume the user also uses hadoop in his /
>> > her deployment. Then he / she should be aware of the deprecation of
>> > metrics.* classes in both hadoop 1.0 and 2.0
>> > Meaning he / she should be prepared to endorse metrics2 framework.
>> >
>> Hadoop deprecating metrics in favor of metrics2 is independent of us
>> deprecating HBase metrics classes.  TimeStampingFileContext is one
>> MetricsContext implementation in HBase that would need to be
>> deprecated and could be used or possibly extended by current users.
>> Ultimately it's up to Lars H as RM for 0.94 to decide what he wants to
>> include.  It just feels to me like we're rushing to deprecate metrics
>> in 0.94 so that it can be removed in 0.96, instead of what seems to me
>> like the more standard path of deprecating metrics in 0.96, while also
>> including new metrics2 implementations, which would give users a
>> smoother path to actually switch over.  I'm just not sure I understand
>> the motivation for deprecating in 0.94 instead of 0.96.

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