.. _rfc47:

=======================================================================
MS RFC 47: Move IGNORE_MISSING_DATA to run-time configuration
=======================================================================

:Date: 2008/10/09
:Author: Paul Ramsey
:Contact: pramsey at cleverelephant.ca
:Last Edited: 2008/10/15
:Status: Adopted on 2008-10-15 - Completed
:Version: MapServer 5.4
:Id: $Id$

Overview 
--------

Making the options for ignoring missing data in tile-indexed layers and WMS
client layers more flexible, and configurable at run-time via the map file.

Technical Solution
------------------

Currently Mapserver has only compile-time (./configure --ignore-missing-data)
control of behavior when files referenced in tile indexes are missing, via the
IGNORE_MISSING_DATA define, and that behavior is applied globally.

Under this RFC, the missing data behavior will be defined:

 * at run time
 * globally for a map file

As well, the option to "fail on a missing layer" will be added to the WMS
client code, which currently defaults to "ignore on a missing layer".

All changes will preserve the current default behavior in cases where new
behavior is not requested by the user: missing data in tileindexes will
continue to cause failure and missing WMS layers will continue to be ignored,
unless Mapserver is compiled with --ignore-missing-data.

A map-level configuration option will be added, CONFIG "ON_MISSING_DATA"
"[ACTION]", with the following valid actions: "IGNORE", "LOG", "FAIL". The
default map-level behavior will be "FAIL", unless MapServer is compiled with
--ignore-missing-data, in which case it will be "LOG". This will preserve the
current behavior for all legacy mapfiles and compile set-ups.

In the case of "LOG" behavior, the logging will only occur if the mapfile is
set up for logging: DEBUG is set and MS_ERRORFILE is set. Documentation must
note that DEBUG and MS_ERRORFILE need to be set.

At the same time, this ticket (#2722) can probably be tracked down and
resolved.

Mapscript Implications
----------------------

None.

Files Affected
--------------

::

 mapshape.c
 mapogr.c
 mapraster.c
 maprasterquery.c

* Documentation will be updated to reflect the new feature

  * Mapserver Mapfile Reference

Backwards Compatibility Issues
------------------------------

None. Legacy mapfiles and compile setups should retain existing behavior in
the presence of this new code.

Bug ID
------

* http://trac.osgeo.org/mapserver/ticket/2785

Voting History
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N/A

References
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N/A