Cache miniconda packages

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The unpacking of freshly downloaded conda packages makes up significant time in our build. Locally this made the conda env creation for Parquet go from 1min to 14s.

Reporter: Uwe Korn / @xhochy
Assignee: Wes McKinney / @wesm

Related issues:

• Arrow 0.3 release (blocks)

_{Note: This issue was originally created as ARROW-646. Please see the migration documentation for further details.}

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Uwe Korn / @xhochy:
PR: #394

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Wes McKinney / @wesm:
@cpcloud @leifwalsh I marked this for 0.3 – with the rampant conda / anaconda.org timeouts, if we can cache our conda tarballs using Travis CI caching we may be able to both speed up builds and reduce flakiness. I think this may involve changing the conda cache directory to be someplace other than the miniconda/ install in https://github.com/apache/arrow/blob/master/ci/travis_install_conda.sh#L27.

[asfimport]

Wes McKinney / @wesm:
PR: #532

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Wes McKinney / @wesm:
Issue resolved by pull request 532
#532