WhatIs: The XIOS library

The XIOS (Xml I/O Server) library is based on client-server principles where the server manages the outputs asynchronously from the client (the climate model) so that the bottleneck of writing data is alleviated.

To compile with XIOS enabled, one must specify the option

 -io xios

to the makelmdz_fcm script.

In addition the flag

ok_all_xml=y

should be set (in the config.def file) or else the default behavior, i.e. outputs controlled and generated by the IOIPSL library, will occur.

XIOS output controls

All aspects of the outputs (name, units, file, post-processing operations, etc.) are controlled by dedicated XML files which are read at run-time. Samples of xml files are provided in the "DefLists" directory.

In a nutshell:

• the master file read by XIOS is iodef.xml; and contains specific XIOS parameters such as using_server to dictate whether XIOS is run in client-server mode (true) or attached (false) mode, info_level to set the verbosity of XIOS messages (0: none, 100: very verbose), print_file to set whether XIOS messages will be sent to standard output (false) or dedicated xios_*.out and xios_*.err files (true).

                        <variable id="using_server" type="bool">false</variable>
                        <variable id="info_level" type="int">0</variable>
                        <variable id="print_file" type="bool"> false </variable>

• It is common practice to have LMDZ-related definitions and outputs in separate XML files, e.g. context_lmdz.xml which are included in iodef.xml via the src attribute, e.g.

       <context id="LMDZ" src="./context_lmdz.xml"/>

The context_lmdz.xml file must then contain all fields/grid/file output definitions, which may be split into multiple XML files. Current practice is to use separate file_def_histsomething_lmdz.xml files, one for each histsomething.nc file to generate, and include these in context_lmdz.xml using the file_definition key. e.g.:

  <!-- Define output files
              Each file contains the list of variables and their output levels -->

  <file_definition src="./file_def_histday_lmdz.xml"/>
  <file_definition src="./file_def_histhf_lmdz.xml"/>
  <file_definition src="./file_def_histins_lmdz.xml"/>
  <file_definition src="./file_def_histLES_lmdz.xml"/>
  <file_definition src="./file_def_histmth_lmdz.xml"/>

08/04/2021