[Zope] Re: Zope 2.9 Product Refreshing

[Tres Seaver]

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James Davies wrote:
> This isn't really a solution. Clients will still lose session data, which is 
> unacceptable.
> 
> -James.
> 
> On Monday 07 August 2006 22:15, Reinoud van Leeuwen wrote:
>> On Mon, Aug 07, 2006 at 10:12:42PM +1000, James Davies wrote:
>>> We have Zeo, but running a seperate instance of zope for each site is
>>> still too much (We probably host around 50 sites at the moment, and
>>> growing. The only economical way to do this is to put multiple sites in
>>> one zope instance).
>> Still you can shutdown 1 ZEO client; update products there and start it up
>> again... There will be some performance degradation but the sites stay
>> up... (and I hope you've got enough ZEO clients so that bringing 1 down
>> will not cause severe problems...)

You have that point-of-failure anyway if you are using the RAM-based
sessions provided by Zope's core sessioning.  If availability is
important to you, then you *need* to be using ZEO and a load balancer,
at which point you also have to look at a more scalable / available
sessioning solution.

There are a couple of alternatives out there:

  - SQL-based session implementaitons (including some which will drop
    into your application "seamlessly"), e.g.:

    http://www.zope.org/Members/anthony/software/SQLSession (really
    old, might need some tweaking).

  - A memcached-based solutions, e.g.:

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

Refresh is dangerous because it mostly works, and because when it
breaks, the breakage surfaces as heisenbugs.  I therefore have a rule
about supporting folks who use refresh:  if they can't reproduce the
problem with refresh disabled, I can't help them.


Tres.
- --
===================================================================
Tres Seaver          +1 202-558-7113          tseaver at palladion.com
Palladion Software   "Excellence by Design"    http://palladion.com
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