Re: [Condor-users] Condor semantics question

[Ian Chesal <ICHESAL@xxxxxxxxxx>]

> 1. What is the difference between a ClassAd and a Job?

ClassAds are a language for describing datasets. On the surface a
ClassAd looks like a collection of key/value pairs but they're
considerably more than that: they're named expressions. See:
http://www.cs.wisc.edu/condor/manual/v7.2/4_1Condor_s_ClassAd.html#36130
and for even more detail http://www.cs.wisc.edu/condor/classad/ --
everything in a Condor system is described by a ClassAd: Jobs,
Schedulers, Execution Slots, etc.

A Job is represented by a ClassAd. Usually it has:

        MyType = "Job"

In it. But maybe not always. Here's a list of all the ClassAd attributes
a job can have:
http://www.cs.wisc.edu/condor/manual/v7.2/Appendix_A_ClassAd.html#76136

> Is the former just a definition and the latter an instance of the
definition
> once submitted?

The former is a representation of a collection of expressions, the
latter is a use of that representation: a Job presents a particular
ClassAd to the Condor system. An execution slot presents another type of
ClassAd. The condor_collector daemon for your system collects all the
different ClassAds from all the different pieces in one place. The
condor_negotiator daemon matches Job ClassAds to execution slot ClassAds
by evaluation both of their ClassAds in a common context in a process
known as matchmaking.

> 2. What is the name given to the outcome or the result from having
>    completed a job? The answer should make it easier for me
>    to grep the documentation for more information.

Outcome results are stored in the Job's ClassAd. When you submit a job
to a condor_schedd daemon it creates a Job ClassAd in the system. That
ClassAd stores the state of the Job throughout its lifecycle. And when
it's done it stores the end state plus some history information.
Depending on how your system is set up that information either hangs
around in the condor_shedd's queue until you clear it, or it gets punted
to the history file in which case you can find it using the
condor_history command. There's also an optional RDBMS piece to Condor
called Quill you can fire up that'll hold on to all the ClassAd
information for you system (including Machine ClassAds so you can see
machine use and job run history by machine) for you.

Hope that helps.

- Ian

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