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From Steve Loughran <ste...@hortonworks.com>
Subject Re: DISCUSS: use SLF4J APIs in new modules?
Date Fri, 11 Apr 2014 08:37:01 GMT
On 10 April 2014 16:38, Karthik Kambatla <kasha@cloudera.com> wrote:

> +1 to use slf4j. I would actually vote for (1) new modules must-use, (2)
> new classes in existing modules are strongly recommended to use, (3)
> existing classes can switch to. That would take us closer to using slf4j
> everywhere faster.
>


#1  appeals to me.

#2 & #3, we'd have a mixed phase but ultimately it'd be good. Maybe have a
policy for a class switch process of
a) switch the LOG declaration, change the imports
b) clean up all log statements, dropping the ifDebug and moving to {}
strings instead of "text"+ "value

or do both at the same time, one class or package at time.


Having a consistent log scheme across all classes makes copying and moving
code easier, especially copy+paste

I think there's some bits of code that takes a commons-log argument as a
parameter. If these are public they'd need to be retained, and we'd have to
add an SLF4J logger equivalent.

-Steve


>
> On Thu, Apr 10, 2014 at 8:17 AM, Alejandro Abdelnur <tucu@cloudera.com
> >wrote:
>
> > +1 pn slf4j.
> >
> > one thing Jay, the issues with log4j will still be there as log4j will
> > still be under the hood.
> >
> > thx
> >
> > Alejandro
> > (phone typing)
> >
> > > On Apr 10, 2014, at 7:35, Andrew Wang <andrew.wang@cloudera.com>
> wrote:
> > >
> > > +1 from me, it'd be lovely to get rid of all those isDebugEnabled
> checks.
> > >
> > >
> > >> On Thu, Apr 10, 2014 at 4:13 AM, Jay Vyas <jayunit100@gmail.com>
> wrote:
> > >>
> > >> Slf4j is definetly a great step forward.  Log4j is restrictive for
> > complex
> > >> and multi tenant apps like hadoop.
> > >>
> > >> Also the fact that slf4j doesn't use any magic when binding to its log
> > >> provider makes it way easier to swap out its implementation then tools
> > of
> > >> the past.
> > >>
> > >>>> On Apr 10, 2014, at 2:16 AM, Steve Loughran <stevel@hortonworks.com
> >
> > >>> wrote:
> > >>>
> > >>> If we're thinking of future progress, here's a little low-level one:
> > >> adopt
> > >>> SLF4J as the API for logging
> > >>>
> > >>>
> > >>>  1. its the new defacto standard of logging APIs
> > >>>  2. its a lot better than commons-logging with on demand Inline
> string
> > >>>  expansion of varags arguments.
> > >>>  3. we already ship it, as jetty uses it
> > >>>  4. we already depend on it, client-side and server-side in the
> > >>>  hadoop-auth package
> > >>>  5. it lets people log via logback if they want to. That's
> client-side,
> > >>>  even if the server stays on log4j
> > >>>  6. It's way faster than using String.format()
> > >>>
> > >>>
> > >>> The best initial thing about SL4FJ is how it only expands its
> arguments
> > >>> string values if needed
> > >>>
> > >>>     LOG.debug("Initialized, principal [{}] from keytab [{}]",
> > principal,
> > >>> keytab);
> > >>>
> > >>> not logging at debug? No need to test first. That alone saves code
> and
> > >>> improves readability.
> > >>>
> > >>> The slf4 expansion code handles null values as well as calling
> > toString()
> > >>> on non-null arguments. Oh and it does arrays too.
> > >>>
> > >>> int array = [1, 2, 3];
> > >>> String undef = null;
> > >>>
> > >>> LOG.info("a = {}, u = {}", array, undef)  -> "a = [1, 2, 3],  u
=
> null"
> > >>>
> > >>> Switching to SLF4J from commons-logging is as trivial as changing the
> > >> type
> > >>> of the logger created, but with one logger per class that does get
> > >>> expensive in terms of change. Moving to SLF4J across the board would
> > be a
> > >>> big piece of work -but doable.
> > >>>
> > >>> Rather than push for a dramatic change why not adopt a policy of
> > >> demanding
> > >>> it in new maven subprojects? hadoop-auth shows we permit it, so why
> not
> > >> say
> > >>> "you MUST"?
> > >>>
> > >>> Once people have experience in using it, and are happy, then we could
> > >> think
> > >>> about switching to the new APIs in the core modules. The only
> > troublespot
> > >>> there is where code calls getLogger() on the commons log to get at
> the
> > >>> log4j appender -there's ~3 places in production code that does this,
> > 200+
> > >>> in tests -tests that do it to turn back log levels. Those tests can
> > stay
> > >>> with commons-logging, same for the production uses. Mixing
> > >> commons-logging
> > >>> and slf4j isn't drastic -they both route to log4j or a.n.other back
> > end.
> > >>>
> > >>> -Stevve
> > >>>
> > >>> --
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> > >>
> >
>

-- 
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NOTICE: This message is intended for the use of the individual or entity to 
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