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75 lines
2.7 KiB
75 lines
2.7 KiB
Frequently Asked Questions |
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:meth:`wrf.getvar` uses more memory when xarray is enabled. Is there a memory leak? |
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The difference in memory usage can be observed when running the following code with |
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and without xarray enabled (see :meth:`wrf.disable_xarray`): |
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.. code:: python |
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from netCDF4 import Dataset |
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import wrf |
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# Uncomment to disable xarray |
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# wrf.disable_xarray() |
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for i in range(150): |
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f = Dataset('wrfout_d01_2005-07-17_12_00_00.nc') |
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p = wrf.getvar(f, 'pressure') |
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f.close() |
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When xarray is enabled, there is an internal thread-local cache used to hold the |
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XLAT and XLONG coordinate variables, along with a boolean variable to remember |
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if a particular file or sequence is from a moving nest. This is useful when |
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working with sequences of WRF files, so that the XLAT and XLONG variables |
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aren't repeatedly extracted. This cache is limited to holding 20 items by |
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default, where the key to each cache entry is the object ID for the file |
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or sequence of files. In this particular example, a new file object is created |
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for each iteration, which will have a new object ID, so the 20 cache spots are |
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going to be filled up. Memory usage will be quite a bit higher for the |
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xarray-enabled case, but the memory usage will eventually top off. |
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There is a function :meth:`wrf.set_cache_size` that can be used to decrease the |
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number of files/sequences in the cache. By setting the cache size to 0, the |
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cache can be disabled completely. |
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Can I use :class:`xarray.Dataset` as an input to the wrf-python functions? |
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-------------------------------------------------------------------------- |
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Currently, wrf-python is designed to use the API for PyNIO and netCDF4-python, |
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which differs from the xarray.Dataset API. However, there is an undocumented |
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feature for Dataset objects that can be used as workaround. Each Dataset |
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object has a :attr:`xarray.Dataset._file_obj.ds` attribute that can be used |
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to obtain the underlying netCDF file object. Keep in mind that this is not in |
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the public API for xarray, so it could break in a future release. |
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Here is an example: |
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.. code:: python |
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import xarray |
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import wrf |
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ds = xarray.open_dataset(FILENAME) |
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slp = wrf.getvar(ds._file_obj.ds, "slp") |
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In a future release of wrf-python, direct support for Dataset objects will |
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be added and this will no longer be necessary. |
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Why is wrf-python taking hours to run? |
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The most likely culprit is insufficient memory for the calculation you are |
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trying to perform. |
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See :ref:`performance` for more information. |
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