openstack/oslo.cache
Code Issues Proposed changes

Merge "Pass flush_on_reconnect to memcache pooled backend"

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Zuul 2019-04-15 14:48:52 +00:00 committed by Gerrit Code Review
commit a8d3c14706
2 changed files with 45 additions and 1 deletions
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22
oslo_cache/_memcache_pool.py
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@ -212,7 +212,27 @@ class MemcacheClientPool(ConnectionPool):
self._hosts_deaduntil = [0] * len(urls)
def _create_connection(self):
return _MemcacheClient(self.urls, **self._arguments)
# NOTE(morgan): Explicitly set flush_on_reconnect for pooled
# connections. This should ensure that stale data is never consumed
# from a server that pops in/out due to a network partition
# or disconnect.
#
# 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.
#
# The normal non-pooled clients connect explicitly on each use and
# does not need the explicit flush_on_reconnect
return _MemcacheClient(self.urls, flush_on_reconnect=True,
**self._arguments)
def _destroy_connection(self, conn):
conn.disconnect_all()

24
releasenotes/notes/bug-1819957-ccff6b0ec9d1cbf2.yaml Normal file
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@ -0,0 +1,24 @@
---
fixes:
- |
[`bug 1819957 <https://bugs.launchpad.net/keystone/+bug/1819957>`_]
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. This change only impacts the pooled backend
as it is the most likely (with heavy use of greenlet) to be impacted
by the problem and is the recommended production configuration.
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.