Check if a hazard calculation is too big before running it

[Michele Simionato]

This is important for OATS-like services. There should be no limits for calculation on our cluster.
The idea is to introduce two parameters in openquake.cfg:

# maximum weight of the sources; 0 means no limit
# for a laptop, a good number is 200,000
max_input_weight = 0

# maximum size of the output in some units; 0 means no limit
# for a laptop, a good number is 2,000,000
max_output_weight = 0

If the limits are set, an user trying to run a computation over the limits (because the input is too large or because the expected output is too large) will get an error right after the pre_execute phase, before the real computation starts.

[Michele Simionato (michele-simionato)]

With the proposed implementation the input weight is given by the number of ruptures generated by the sources; for point sources however a corrective factor given by the parameter `point_source_weight` (currently 1/40) is applied.
The output weight is a pure number which is proportional to the size of the expected output of the calculator. For classical and disaggregation calculators it is given by n_sites * n_realizations * n_levels; for the event based calculator is given by n_sites * n_realizations .

[Michele Simionato (michele-simionato)]

https://github.com/gem/oq-engine/pull/1497