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Update the wheel-cache-disabling docs with our latest understanding of C compiler nondeterminism.

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Erik Rose 2015-10-21 16:35:30 -04:00
parent f38fc903f2
commit 4488047ef6
1 changed files with 7 additions and 4 deletions
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docs/reference/pip_install.rst
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@ -516,10 +516,13 @@ those wheels would be selected for installation, but their hashes would not
match the sdist ones from the requirements file. A further complication is that match the sdist ones from the requirements file. A further complication is that
locally built wheels are nondeterministic: contemporary modification times make locally built wheels are nondeterministic: contemporary modification times make
their way into the archive, making hashes unpredictable across machines and their way into the archive, making hashes unpredictable across machines and
cache flushes. However, wheels fetched from index servers land in pip's HTTP cache flushes. Compilation of C code adds further nondeterminism, as many
cache, not its wheel cache, and are used normally in hash-checking mode. The compilers include random-seeded values in their output. However, wheels fetched
only potential penalty is thus extra build time for sdists, and this can be from index servers are the same every time. They land in pip's HTTP cache, not
solved by making sure pre-built wheels are available from the index server. its wheel cache, and are used normally in hash-checking mode. The only downside
of having the the wheel cache disabled is thus extra build time for sdists, and
this can be solved by making sure pre-built wheels are available from the index
server.
Hash-checking mode also works with :ref:`pip download` and :ref:`pip wheel`. A Hash-checking mode also works with :ref:`pip download` and :ref:`pip wheel`. A
:ref:`comparison of hash-checking mode with other repeatability strategies :ref:`comparison of hash-checking mode with other repeatability strategies