[Bug 1096867] [NEW] Split area sources into point sources (to improve distribution of calculation load)

[Damiano Monelli]

Public bug reported:

Currently, hazard calculations are parallelized over sources (i.e. a
task is created for each source in a source model).

In case of source models made of 'area sources' the current distribution
mechanism can produce an unevenly distribution of computational load (in
a single source model, area sources can have very different sizes and
therefore the number of ruptures - and the required computation time -
can vary a lot). In this case a calculation can last for a long time
simply because a task is assigned to a large area source. Moreover this
prevent an efficient utilization of the computational infrastructure.

This problem can be reduced if an area source is indeed considered as a
collection of point sources (as it is actually done in NHLIB, an area
source is an extension of a point source, see:
https://github.com/gem/nhlib/blob/master/nhlib/source/area.py#L24).

The 'splitting mechanism' can be be implemented as follows:

1) Given an area source, discretize the area source region
(https://github.com/gem/nhlib/blob/master/nhlib/geo/polygon.py#L177)

2) Create a 'scaled' version of the original area source magnitude
frequency distribution (mfd), that is take the original area source mfd
and create a new evenly discretized mfd
(https://github.com/gem/nhlib/blob/master/nhlib/mfd/evenly_discretized.py#L22)
having occurrence rates equal to the original ones divided by the total
number of points in the discretized polygon computed in 1)

3) For each point in the discretized polygon computed in 1) create a
point source
(https://github.com/gem/nhlib/blob/master/nhlib/source/point.py#L27),
with the same attributes of the original area source but with the scaled
mfd

A task can then be created for each point source.

** Affects: openquake
Importance: Undecided
Status: New

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https://bugs.launchpad.net/bugs/1096867

Title:
Split area sources into point sources (to improve distribution of
calculation load)

Status in OpenQuake:
New

Bug description:
Currently, hazard calculations are parallelized over sources (i.e. a
task is created for each source in a source model).

In case of source models made of 'area sources' the current
distribution mechanism can produce an unevenly distribution of
computational load (in a single source model, area sources can have
very different sizes and therefore the number of ruptures - and the
required computation time - can vary a lot). In this case a
calculation can last for a long time simply because a task is assigned
to a large area source. Moreover this prevent an efficient utilization
of the computational infrastructure.

This problem can be reduced if an area source is indeed considered as
a collection of point sources (as it is actually done in NHLIB, an
area source is an extension of a point source, see:
https://github.com/gem/nhlib/blob/master/nhlib/source/area.py#L24).

The 'splitting mechanism' can be be implemented as follows:

1) Given an area source, discretize the area source region
(https://github.com/gem/nhlib/blob/master/nhlib/geo/polygon.py#L177)

2) Create a 'scaled' version of the original area source magnitude
frequency distribution (mfd), that is take the original area source
mfd and create a new evenly discretized mfd
(https://github.com/gem/nhlib/blob/master/nhlib/mfd/evenly_discretized.py#L22)
having occurrence rates equal to the original ones divided by the
total number of points in the discretized polygon computed in 1)

3) For each point in the discretized polygon computed in 1) create a
point source
(https://github.com/gem/nhlib/blob/master/nhlib/source/point.py#L27),
with the same attributes of the original area source but with the
scaled mfd

A task can then be created for each point source.

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[Lars Butler]

** Changed in: openquake
Status: New => Confirmed

** Changed in: openquake
Importance: Undecided => High

** Changed in: openquake
Assignee: (unassigned) => Lars Butler (lars-butler)

** Changed in: openquake
Milestone: None => 0.9.1

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https://bugs.launchpad.net/bugs/1096867

Title:
Split area sources into point sources (to improve distribution of
calculation load)

Status in OpenQuake:

Confirmed

[Lars Butler]

** Tags added: hazard optimization

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https://bugs.launchpad.net/bugs/1096867

Title:
Split area sources into point sources (to improve distribution of
calculation load)

Status in OpenQuake:

Confirmed