Overview

The 'mcdutils' product supplies a replacement for the ZODB-based session data container supplied by the 'Transience' product, shipped with the Zope core. Rather than using a ZODB storage as the backing store for eession data, as 'Transience' does, 'mcdutils' stores session data in a cluster of one or more 'memcached' servers.

This approach is a bit of a cheat, as it uses the daemons as primary stores, rather than as caches for results of an expensive query. Nevertheless, the semantics are not a bad match for typical session usage.

Installing the Product

Unpack the tarball, and then move or link the 'mcdutils' subdirectory into your '$INSTANCE_HOME/Products' directory, and restart Zope.

Configuring Zope to Store Sessions in 'memcached'

1. After installation, add an instance of the 'MemCache Proxy' type from the ZMI add list, typically in the root of your ZODB, and give it a memorable name, e.g., 'mcproxy'.
2. Configure the proxy using its "Properties" tab. Set the 'servers' property to a list of servers, one per line, where each line is in the format, '<host>:<port'. For instance, to use the 'memcached' running on the default port on your local machine, the value would be 'localhost:11211'.
3. Add an instance of the 'MemCache Session Data Container' type, e.g. 'mcsdc' in the root.
4. Configure that instance on its "Properties" tab to use the proxy you created above (e.g., '/mcproxy').
5. Finally, on the main tab of your 'session_data_manager' instance (typically also in the root), change the 'Transient Object Container Path' value to match the location of your new proxy, e.g. '/mcsdc'.

You can test the memcached configuration on its "Test" tab. Enter one or more lines describing key-value pairs, where the "key" for your session is separated from the value by the first space character. Note that the session values are displayed below the form.

Resources

• The main memcached site explains the memcached architecture, and contains information on administering and tuning a memcached cluster.

  o http://www.danga.com/memcached/

• The Python client bindings for memcached are maintained by

  Sean Reifschneider at Tummy.com:

  o http://www.python.org/pypi/memcached/1.2_tummy6

• 'tugela' is an alternate cache daemon implementation, which stores its mapping using a Berkeley b-tree on disk. It conforms to the same wire protocol as 'memcached':

  o http://meta.wikimedia.org/wiki/Tugela_Cache

• This product's home page and bug tracker:

  o http://agendaless.com/Members/tseaver/software/mcdutils

  o http://agendaless.com/Members/tseaver/software/mcdutils/issues