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[Chris Dent <cdent+lp@xxxxxxxxxxxxx>]

Public bug reported:

Most requests to the placement service eventually reach the database
code in the resource_provider.py file and as a result eventually run
_ensure_trait_sync to make sure that this process has synced the os-
traits library to its traits database table.

While there is a flag to make sure that the syncing doesn't happen if it
already happened before, we lock around checking that flag for nearly
every request. This isn't the end of the world, but it is wasted
activity and it can make a lot of noise in the logs if you're running
DEBUG:

2018-03-15 17:35:37.653 7 DEBUG oslo_concurrency.lockutils [req-7904bbbe-52f7-420f-b058-13779dc018d1 admin admin - - -] Acquired semaphore "trait_sync" lock /usr/lib/python3.6/site-packages/oslo_concurrency/lockutils.py:212
2018-03-15 17:35:37.653 7 DEBUG oslo_concurrency.lockutils [req-7904bbbe-52f7-420f-b058-13779dc018d1 admin admin - - -] Releasing semaphore "trait_sync" lock /usr/lib/python3.6/site-packages/oslo_concurrency/lockutils.py:228

This is redundant. I'm pretty sure I wrote this code, so I'm not sure
what I was thinking, probably cargo culting off ensuring the resource
classes. We only need to sync the traits to the database once and we
only need to check if it has been done once per process. The traits are
read from a python module that is only imported once per process.

So, what we could do is move the calling of ensure_trait_sync to the
part of placement that establishes the database connection facade
thingie. If we merge https://review.openstack.org/#/c/541435/ (which
moves placement database connection establishment to its own file) or
something like it, we have an easy place to do it, at server boot time.

We find the session, make a context, do the sync, set the global and
never worry about it again. All the _ensure_trait_sync calls can be
removed.

** Affects: nova
     Importance: Low
         Status: Triaged


** Tags: placement

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https://bugs.launchpad.net/bugs/1756151

Title:
  placement os-traits sync checked every request

Status in OpenStack Compute (nova):
  Triaged

Bug description:
  Most requests to the placement service eventually reach the database
  code in the resource_provider.py file and as a result eventually run
  _ensure_trait_sync to make sure that this process has synced the os-
  traits library to its traits database table.

  While there is a flag to make sure that the syncing doesn't happen if
  it already happened before, we lock around checking that flag for
  nearly every request. This isn't the end of the world, but it is
  wasted activity and it can make a lot of noise in the logs if you're
  running DEBUG:

  2018-03-15 17:35:37.653 7 DEBUG oslo_concurrency.lockutils [req-7904bbbe-52f7-420f-b058-13779dc018d1 admin admin - - -] Acquired semaphore "trait_sync" lock /usr/lib/python3.6/site-packages/oslo_concurrency/lockutils.py:212
  2018-03-15 17:35:37.653 7 DEBUG oslo_concurrency.lockutils [req-7904bbbe-52f7-420f-b058-13779dc018d1 admin admin - - -] Releasing semaphore "trait_sync" lock /usr/lib/python3.6/site-packages/oslo_concurrency/lockutils.py:228

  This is redundant. I'm pretty sure I wrote this code, so I'm not sure
  what I was thinking, probably cargo culting off ensuring the resource
  classes. We only need to sync the traits to the database once and we
  only need to check if it has been done once per process. The traits
  are read from a python module that is only imported once per process.

  So, what we could do is move the calling of ensure_trait_sync to the
  part of placement that establishes the database connection facade
  thingie. If we merge https://review.openstack.org/#/c/541435/ (which
  moves placement database connection establishment to its own file) or
  something like it, we have an easy place to do it, at server boot
  time.

  We find the session, make a context, do the sync, set the global and
  never worry about it again. All the _ensure_trait_sync calls can be
  removed.

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