The eightfold way to the event based calculator

As the readers of this blog already know, the event based calculator is very complex. A summary of the status of the different versions of it is needed. This post attempts to clarify the situation.

First of all, let me dispel the notion that there is a single event based calculator: currently the engine contains at least eight different event based calculators and, depending on how you count them, the number could grow. Here I am referring to the current master, i.e. to what will become version 1.5 of the OpenQuake engine. There are the following event based calculators.

1. The old rupture calculator. This is a calculator which is able to process a source model and produce ruptures which are then stored in the database. This calculator has been in the engine at least for a couple of years. Originally (i.e. before 1.0) it was integrated in the event based hazard calculator.

2. The old GMFs and curves calculator. This is a calculator which is able to process the ruptures produced by calculator #1 and to produce ground motion fields and/or hazard curves. It has been in the engine for a couple of years. Originally it was integrated in the event based hazard calculator. This calculator could be split in two, since the hazard curves functionality could be extracted.

3. The old risk calculator. This is a calculator which is able to process the GMFs produced by calculator #2 and to produce risk results. It has been in the engine for years, having experienced several refactorings to simplify the database queries and to reduce the time spent to retrieve the GMFs and the needed memory. In this way, its performance has been substantially improved over time: still, it is too poor for large scale calculations. For this reason a new revolutionary approach that does not need to read the GMFs has been implemented in calculator #6.

4. The new rupture calculator. It does the same job than calculator #1, but it stores the ruptures in the file system instead than in the database and so it is much faster, especially when the number of stochastic event set is big.

5. The new GMFs and curves calculator. It does the same job than calculator #2, but it stores the GMFs and curves in the file system in HDF5 format instead than in the database. It is much faster than the original calculator. As input, it requires the ruptures produced by the calculator #4.

6. The new event loss table calculator. It does much more than calculator #3, because it is able to compute the ground motion fields on-the-fly (i.e. it has no need of calculator #5, which is there only for debugging and analysis purposes) but it produces much less outputs. At the moment it only computes the event loss table; nevertheless, its feature set is growing. This calculator does not need the database and saves the event loss table in HDF5 format, so it is orders of magnitude faster than the original calculator. Also, it requires orders of magnitude less memory.

7. The experimental oq-lite risk calculator. This is a full featured replacement of calculator #3, but it is still a work in progress and has known limitations. It is possible that in the future it will be merged with calculator #6.

8. The BCR event based calculator. This is an old calculator which has still no counterpart not relying on the database. But such counterpart is scheduled to appear soon.

Once all the features of the original event based risk and BCR calculator are ported to the new database-less system, it will become possible to remove the old calculators and probably we will be down to only 4 calculators (I say probably because new variations of the event based calculator could appear). Unfortunately, for the moment the situation is a bit of a mess.

Also, it should be noted that the event based calculators work in a completely different way if sampling is enabled (number_of_logic_tree_samples > 0): actually, it would be better to consider them different calculators, since the calculation logic, the performance figures and the outputs are quite different. So the 8 event based calculators should be counted as 16!