Philippe 20/09/2024: IO: set NOFILL by default for netCDF files

src/LIB/SURCOUCHE/src/mode_io_file_nc4.f90

@@ -28,8 +28,8 @@ use modd_precision,    only: CDFINT
 use mode_io_tools_nc4, only: IO_Err_handle_nc4, IO_Knowndims_set_nc4, IO_Iocdf_alloc_nc4
 use mode_msg
 
-use NETCDF,            only: NF90_CLOBBER, NF90_GLOBAL, NF90_NETCDF4, NF90_NOERR, NF90_NOWRITE,  &
-                             NF90_CLOSE, NF90_CREATE, NF90_GET_ATT, NF90_INQUIRE, NF90_INQUIRE_ATTRIBUTE, &
+use NETCDF,            only: NF90_GLOBAL, NF90_NETCDF4, NF90_NOERR, NF90_NOWRITE,            &
+                             NF90_CLOSE, NF90_GET_ATT, NF90_INQUIRE, NF90_INQUIRE_ATTRIBUTE, &
                              NF90_OPEN, NF90_PUT_ATT, NF90_STRERROR
 
 implicit none
@@ -44,10 +44,13 @@ subroutine IO_File_create_nc4(tpfile,hprogram_orig)
   use mode_io_tools,            only: IO_Filename_construct
   use mode_io_tools_mnhversion, only: IO_Mnhversion_set
 
+  use NETCDF, only: NF90_CLOBBER, NF90_CREATE, NF90_NOFILL, NF90_SET_FILL
+
   type(tfiledata),           intent(inout) :: tpfile
   character(len=*),optional, intent(in)    :: hprogram_orig !to emulate a file coming from this program
 
   character(len=:),allocatable :: yfilem  ! name of the file
+  integer(kind=CDFINT)         :: ioldmode
   integer(kind=CDFINT)         :: istatus
 
   call print_msg(NVERB_DEBUG,'IO','IO_File_create_nc4','called for '//trim(tpfile%cname))
@@ -60,6 +63,14 @@ subroutine IO_File_create_nc4(tpfile,hprogram_orig)
     if (istatus /= NF90_NOERR) then
       call print_msg(NVERB_FATAL,'IO','IO_File_create_nc4','NF90_CREATE for '//trim(yfilem)//'.nc: '//NF90_STRERROR(istatus))
     end if
+
+    ! Set pre-filling to NF90_NOFILL
+    ! In theory, this should give better performance
+    istatus = NF90_SET_FILL( tpfile%nncid, NF90_NOFILL, ioldmode )
+    if (istatus /= NF90_NOERR) then
+      call print_msg(NVERB_FATAL,'IO','IO_File_create_nc4','NF90_CREATE for '//trim(yfilem)//'.nc: '//NF90_STRERROR(istatus))
+    end if
+
     call IO_Not_cleanly_closed_set_nc4(tpfile)
     call IO_Knowndims_set_nc4(tpfile, hprogram_orig=hprogram_orig)
   end if

src/LIB/SURCOUCHE/src/mode_io_write_nc4.f90

@@ -553,6 +553,11 @@ if ( istatus /= NF90_NOERR ) then
   istatus = NF90_DEF_VAR( tpfile%nncid, yvarname, itype, ivdims, ivarid )
   if ( istatus /= NF90_NOERR ) call IO_Err_handle_nc4( istatus, 'IO_Field_create_nc4', 'NF90_DEF_VAR', Trim( yvarname ) )
 
+  ! Set pre-filling to NF90_NOFILL
+  ! Not done here because already set at creation time with NF90_SET_FILL
+  ! istatus = NF90_DEF_VAR_FILL( tpfile%nncid, ivarid, NF90_NOFILL, 0. )
+  ! if ( istatus /= NF90_NOERR ) call IO_Err_handle_nc4( istatus, 'IO_Field_create_nc4', 'NF90_DEF_VAR_FILL', Trim( yvarname ) )
+
   ! Add compression if asked for
   if ( tpfile%lnccompress .and. tpfield%ntype == TYPEREAL .and. tpfield%ndims >= 1 ) then
     istatus = NF90_DEF_VAR_DEFLATE( tpfile%nncid, ivarid, SHUFFLE, DEFLATE, tpfile%nnccompress_level )