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.. note that if this is changed from the default approach of using an *include*
(in index.rst) to a separate performance page, the header needs to be changed
from === to ***, the filename extension needs to be changed from .inc.rst to
.rst, and a link needs to be added in the subpackage toctree
.. _astropy-io-fits-performance:
Performance Tips
================
It is possible to set the data array for :class:`~astropy.io.fits.PrimaryHDU`
and :class:`~astropy.io.fits.ImageHDU` to a `dask <https://dask.org/>`_ array.
If this is written to disk, the dask array will be computed as it is being
written, which will avoid using excessive memory:
.. doctest-requires:: dask
>>> import dask.array as da
>>> array = da.random.random((1000, 1000))
>>> from astropy.io import fits
>>> hdu = fits.PrimaryHDU(data=array)
>>> hdu.writeto('test_dask.fits')
.. TODO: determine whether the following is quantitatively true, and either
.. uncomment or remove.
.. Performance Tips
.. ================
..
.. By default, :func:`astropy.io.fits.open` will open files using memory-mapping,
.. which means that the data is not necessarily read into memory until it is
.. needed. While memory-efficient, if memory is not a concern for you, you may
.. find that you can get better performance by turning memory mapping off, which
.. forces the data to be read into memory immediately:
..
.. .. doctest-skip::
..
.. >>> fits.open('example.fits', memmap=False)
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