Changes between Version 2 and Version 3 of 2019WP/HPC-11_Mirek_Andrejczuk_IO_with_XIOS

Timestamp:

2019-12-05T16:46:26+01:00 (4 years ago)

Author:

smasson

Comment:

--

2019WP/HPC-11_Mirek_Andrejczuk_IO_with_XIOS

@@ -34 +34 @@
 == Review
 
-{{{#!box help
-[[Include(wiki:Developers/DevProcess#review)]]
-}}}
+Some years ago, when we created iom.F90, the idea was to be able to use different IO libraries as transparently as possible...
+
+This was still the case in NEMO 3.6.
+In that version, you could find 3 different IO libraries: nf90, ioipsl and dimg.
+the choice between theses libraries was done in iom_def.F90 (lines 30 to 37)
+https://forge.ipsl.jussieu.fr/nemo/browser/NEMO/releases/release-3.6/NEMOGCM/NEMO/OPA_SRC/IOM/iom_def.F90 [[BR]]
+
+ 
+The iom routines where therefore organized in a 2 stages modules.
+
+- The first stage is iom.F90 that contains all public subroutines, prepare all the IO work but do the IO work.
+All the idea was iom.F90 is the common interface for all IO libraries.
+https://forge.ipsl.jussieu.fr/nemo/browser/NEMO/releases/release-3.4/NEMOGCM/NEMO/OPA_SRC/IOM/iom.F90
+
+ - The second stage is called by iom.F90 subroutines and consist in 3 different IO routines
+https://forge.ipsl.jussieu.fr/nemo/browser/NEMO/releases/release-3.6/NEMOGCM/NEMO/OPA_SRC/IOM/iom_nf90.F90
+https://forge.ipsl.jussieu.fr/nemo/browser/NEMO/releases/release-3.6/NEMOGCM/NEMO/OPA_SRC/IOM/iom_ioipsl.F90
+https://forge.ipsl.jussieu.fr/nemo/browser/NEMO/releases/release-3.6/NEMOGCM/NEMO/OPA_SRC/IOM/iom_rstdimg.F90
+
+
+The fork toward the different libraries was done in iom.F90, with case statements. 
+See for example iom_rstput interface in this version of iom.F90 (from line 1046) 
+
+We think that the use of xios to read/write restarts should try follow this same logic. 
+ -> reintroduce case in iom to be able to switch from native netcdf (nf90) to xios library [[BR]]
+ -> Ideally, the use of xios for restarts should not be visible somewhere else, no? [[BR]]
+ -> once the interface is done it is directly usable for all restarts [[BR]]
+
+We know that the reality is more complex that this simple description and developing such interface wont be so easy…
+We think a good stating point is to follow what is done for nf90 restarts that are performed in 2 steps:
+ 1) 1 time step before restart: define all the restart file using a specific context (so xios_context_initialize and xios_close_context_definition cand be done anytime)[[BR]]
+ 2) fill the file when is it restart time step.
+
+
+Sebastien and Clement