Comment 5 for bug 1819957

Reviewed: https://review.openstack.org/644774
Committed: https://git.openstack.org/cgit/openstack/oslo.cache/commit/?id=1192f185a5fd2fa6177655f157146488a3de81d1
Submitter: Zuul
Branch: master

commit 1192f185a5fd2fa6177655f157146488a3de81d1
Author: Morgan Fainberg <email address hidden>
Date: Fri Mar 22 12:35:16 2019 -0700

    Pass `flush_on_reconnect` to memcache pooled backend

    If a memcache server disappears and then reconnects when multiple memcache
    servers are used (specific to the python-memcached based backends) it is
    possible that the server will contain stale data. The default is now to
    supply the ``flush_on_reconnect`` optional argument to the backend. This
    means that when the service connects to a memcache server, it will flush
    all cached data in the server. The pooled backend is more likely to
    run into issues with this as it does not explicitly use a thread.local
    for the client. The non-pooled backend was not touched, it is not
    the recommended production use-case.

    See the help from python-memcached:

        @param flush_on_reconnect: optional flag which prevents a
     scenario that can cause stale data to be read: If there's more
     than one memcached server and the connection to one is
     interrupted, keys that mapped to that server will get
     reassigned to another. If the first server comes back, those
     keys will map to it again. If it still has its data, get()s
     can read stale data that was overwritten on another
     server. This flag is off by default for backwards
     compatibility.

    Change-Id: I3e335261f749ad065e8abe972f4ac476d334e6b3
    closes-bug: #1819957