Checkpoint / Restart¶

ERF has a standard sort of checkpointing and restarting capability and uses the native AMReX format for reading and writing checkpoints. Each native checkpoint contains a provenance block in job_info. The block records the checkpoint artifact, the ERF execution that wrote it, and the known restart ancestry. See Provenance and Restart Lineage. In the inputs file, the following options control the generation of checkpoint files (which are really directories):

The computational cost associated with reading and writing checkpoint files is typically negligible relative to the overall cost of the simulation; in a recent performance study the cost of writing a checkpoint file was roughly a percent of the cost of a single timestep.

Writing the Checkpoint “Files”¶

List of Parameters¶

Parameter	Definition	Acceptable Values	Default
erf.check_file	prefix for restart files	String	“chk”
erf.check_int	how often (by level-0 time steps) to write restart files	Integer \(> 0\)	-1
erf.check_per	how often in simulation time to write restart files	Real \(> 0\)	-1.0

Restarting¶

10 Restart parameters¶
Parameter	Definition	Acceptable values	Default
`erf.restart` or `amr.restart`	Checkpoint directory from which to restart. `amr.restart` takes precedence if both are set.	String	Not used if unset

Examples of Usage¶

erf.check_file = chk_run
erf.check_int = 10

means that restart files (really directories) starting with the prefix “chk_run” will be generated every 10 level-0 time steps. The directory names will be chk_run00000, chk_run00010, chk_run00020, etc.
erf.check_per = 5.0

means that restart files (really directories) starting with the prefix “chk_run” will be generated whenever the simulation time passes a multiple of 5.0. The directory names will reflect the integer number of steps which have elapsed.

To restart from chk_run00061, for example, set erf.restart to that directory:

erf.restart = chk_run00061

ERF also accepts amr.restart for compatibility with AMReX and existing regression inputs. When both keys are present, amr.restart takes precedence because ReadParameters() queries it after erf.restart.