What Happens When Running a Simulation?

Here are the steps that occur when you start a run via the start_run script:

• It copies files from the baseyear cache into a cache for the current run.
• It adds a row to the run_activity table in the services database, using a new run_id value unique to this run. In order to help match runs with their cache directory, the name of the cache directory begins with the run_id value, e.g. run_342.2006_04_25_09_40.
• For each simulated year:
  • Forks a new process to run the set of UrbanSim models for this year. The set of models to be run is specified by the configuration. Using a separate process helps reduce memory usage, and helps reduce the impact of problems such as memory leaks. This process writes a log file named, e.g., year_2003_log.txt.
• The run activity table includes status information about the run. If the simulation succeeds, it will add another row to the run activity indicating it is done. If the simulation fails, it will add a row indicating that. The run activity also contains a copy of the configuration, which is used when restarting a run.
• Whenever a row is added to the run_activity table, a row is either added or updated in the available_runs table in the services database. This table has a single row per run and records the row's current state and information.