[Developers] optimising the size of checkpoints

[Thomas Radke]

Currently the checkpoint methods available in Cactus save all the 
timelevels of all grid variables which have storage allocated, resulting 
in a maximum-size checkpoint.
At least for some variables (eg. NaNChecker::NaNmask or other analysis 
grid functions), checkpointing doesn't seem necessary; other variables, 
especially scalars (eg. IOBasic::next_info_output_time), can be easily 
recomputed after recovery, thus saving another item in the checkpoint 
plus its attached metadata (which in this case would be larger than the 
actual data).

I propose to tag such grid variables with something like 'CHECKPOINT = 
no' in a thorn's interface.ccl. The checkpoint routines could then query 
the tags table and save only non-tagged variables.
Of course, one would also have to add the logic to properly initialise 
tagged variables in CCTK_POST_RECOVER_VARIABLES if need to.

Comments ?


-- 
Cheers, Thomas.