SWGuideSelectingBranchesForOutput < CMSPublic

CMSPublic Web>SWGuide>SWGuideFrameWork>SWGuideSelectingBranchesForOutput (2011-07-28, WilliamTanenbaum) (raw view)

---+!! How to Configure Output Modules
%COMPLETE3%

%TOC{title="Contents:"}%

---++ Goal of this page

This document describes how to configure output modules.
In CMSSW_0_4_0_pre2, 
configuration of output modules has undergone a significant change;
this document describes only the new system.

---++ Example of Configuration

As are all other framework modules,
output modules are configured
using a =edm::ParameterSet= instance.
In addition to whatever other parameters
a specific output module class may require,
_all_ output module classes allow the parameter
*outputCommands*.
This parameter is of type =vector= of =string=,
and carries zero or more "commands"
that determine which branches in the =Event=
are to be written out by that output module.

An example configuration is:

<verbatim>
cms.untracked.vstring(
              'keep *',
              'drop *_*_*_HLT',
              'keep FEDRawDataCollection_*_*_*'
)
</verbatim>

This configuration tells the system to:

   1. Write out (keep) all branches, except ...
   2. Do not write out (drop) all branches from the HLT process, except ...
   3. Write out all products of type !FEDRawDataCollection.

Commands are applied in the order of presentation in the vector.
Each command carries an _action_ (keep or drop)
and a _specification_ (_e.g._ *_*_*_HLT).
The specification is compared to each branch name.
The specification matches the branch name
if all four fields of the branch name
match the corresponding fields of the specification.
The four fields are separated by underscores.  NOTE: implicitly the first command is always ='drop *'= . 
Therefore if you want to only specify =drop= commands you should use a ='keep *'= as the first command.

A special case is when the entire specification is the
one character "*".  This is interpreted as "*_*_*_*".
In all other cases, exactly 3 underscores must appear
in the specification.  The fields must contain only
alphanumeric characters or one of two available wildcards.
The wildcard "*" will match zero or more characters and these
characters can be anything.
The wildcard "?" will match exactly one character and that
character can be anything.  One restriction is that these
wildcards will only match a sequence of characters contained
inside one of the four fields.  They can match an entire field or
some smaller part of a field, but nothing larger. All 3 underscores
must explicitly appear in the specification.
(Prior to release 1_3_0_pre1, the ? wildcard
was not available and the * wildcard would only match an entire
field and nothing smaller)

If no parameter named "outputCommands" is found,
then a default value is used. The default value is:

<verbatim>
cms.untracked.vstring(
        'keep *'
)
</verbatim>

and so by default all objects are written by a module
so configured.

Note:  If a class has been declared non-persistent, any branch consisting of !EDProduct of that exact class will never be output.  For more information, see the appropriate section in SWGuideCreatingNewProducts
---+++ Real life examples
See [[http://cmslxr.fnal.gov/lxr/source/Configuration/EventContent/python/EventContentCosmics_cff.py][Configuration/EventContent/python/EventContentCosmics_cff.py]] or [[http://cmslxr.fnal.gov/lxr/source/Configuration/EventContent/python/EventContent_cff.py][EventContent/python/EventContent_cff.py]]

---++ The simple output writing algorithm.

For purposes of understanding the behavior of the output,
the algorithm used behaves as if it did the following:

   1. All branches are assigned a 'write bit' set to =false=.
   2. Each command is applied to each branch.
      a. if the specification in the command matches the branch name,
         the branch's 'write bit' is set to the value determined
    by the 'action' of the rule (keep sets it to =true=,
    drop sets it to =false=)
      b. if the specification in the command does not match the
         branch name, the 'write bit' for the branch is not changed.
   3. Commands are considered in the order of their appearance
      in the vector, so that later commands can override the
      actions of earlier commands.

---++ Note on branch names

Branch names have a four-part form with
the format: *PT_ML_IN_PN*

   1. PT is the _product type_; this is also called the "friendly class name".
   1. ML is the _module label_; this is the label of the module that created the product.
   1. IN is the _instance name_; this may be (and often is) a zero-length string.
   1. PN is the _process name_; this is the name of the process in which this object was created.

Most people will probably never see this or need to know this, but in some places
the same branch name will occur with a period appended to the end.  This is required
for some purposes by ROOT.  This period should not be used in "keep" or
"drop" statements.

#ReviewStatus
---++ Review Status

| *Reviewer/Editor and Date (copy from screen)* | *Comments* |
| Main.William Tanenbaum - 14 Jan 2007 | page last content editor  |
| Main.JennyWilliams - 31 Jan 2007 | editing to include in SWGuide  |

<!-- In the following line, be sure to put a blank space AFTER your name; otherwise the Summary doesn't come out right. -->
%RESPONSIBLE% Main.WilliamTanenbaum %BR%
%REVIEW% [[mailto:malik@fnal.gov][Sudhir Malik]]- 24 January 2009

Topic revision: r17 - 2011-07-28 - WilliamTanenbaum

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