[Bug 1655452] Re: netaddr cached indexes are not coherent when changes occur to OUI or IAB data

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** Changed in: netaddr
       Status: Unknown => New

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https://bugs.launchpad.net/bugs/1655452

Title:
  netaddr cached indexes are not coherent when changes occur to OUI or
  IAB data

Status in MAAS:
  Opinion
Status in MAAS 2.1 series:
  Opinion
Status in netaddr:
  New
Status in python-netaddr package in Ubuntu:
  Confirmed

Bug description:
  For some background, see Launchpad bug #1655447.[1]

  The `netaddr.eui.ieee` package is responsible for indexing IEEE data
  at build time, and generating index files that the `netaddr` upstream
  code ships with.

  This works fine until you have a long-running process relying on the
  data. For long-running processes, the index is cached the first time
  the OUI class is used (or the `netaddr.eui.ieee` package is imported).
  That means if `netaddr` is updated to a more recent version while the
  process is running, undefined behavior occurs until the process is
  restarted. This is because the cache becomes out-of-sync with the IEEE
  data on disk. (For example, we have observed `netaddr` crashing with
  an `IndexError` in Launchpad bug #1655049.[2])

  In order to use `netaddr` in a long-running process, the cache must be
  re-read from disk if it changes.

  Ideally, `netaddr` could also employ some type of integrity check,
  such as metadata in the cache file to ensure it is consistent with the
  data on-disk. Since a thorough integrity check might be expensive
  enough to defeat the purpose of an on-disk index, a basic sanity check
  (such as file size; possibly a hash of a subset of the file) should be
  sufficient.

  Alternatively, the on-disk cache of the index could be dropped, and it
  could be calculated in memory. (Then recalculated if the data file
  changes.) However, this may be a problem on embedded systems without
  much CPU power.

  ---

  [1]: https://launchpad.net/bugs/1655447
  [2]: https://launchpad.net/bugs/1655049

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