[ZODB-Dev] zeo 2 availability, plans?

[Jeremy Hylton]

>>>>> "MM" == Mark McEahern <mark@mceahern.com> writes:

  MM> Hi, we're currently planning a consulting project for a customer
  MM> using Zope and we'd like to use ZEO.  I understand that scaling
  MM> the ZSS (Zope Storage Server) is part of the second phase of
  MM> ZEO2 development:

I think you're concluding too much from what some old web pages say
<0.5 wink>.  The ZEO FAQ is more than 2 years old.  (I didn't even
know it existed.)  When we started the ZEO2 project, we rather loosely
described the project as having two phases.  Actual development never
really followed the plan.

Responding a little out of order:

  MM> I couldn't find a timetable for this development.  I'm curious
  MM> whether there is one.  Is anyone using the latest development
  MM> version 2.0b1?  I'm just trying to get a sense of whether I
  MM> should stick with 1.0 and plan to upgrade or whether I should
  MM> play with 2.0b1 because 2.0 final is around the corner?

2.0 final is around the corner.  I expect we'll do one more beta and
get the final release out sometime in September.  This isn't a
timetable, just my guess about how much time we'll have to work on it.

Guido has been looking into the ZEO client cache behavior.  I expect
we'll implement a new cache, but probably push that off until ZEO 2.1.

We've have one customer who has been using ZEO 2 in production for
about a month.  The only issue that has come up with them is a
performance problem that Toby Dickenson diagnosed just after they went
into production.  We're also use ZEO 2 for new customer work that
hasn't gone into production yet.

While it's possible that the ZEO 2 code still has some bugs that will
only be wrung out after serious production use, I think it's about as
stable as ZEO 1.  As ZEO 2 gets closer to a final release, I expect
we'll invest much less time in maintaining ZEO 1.

  MM> <quote> Doesn't this just move the point of failure somewhere
  MM> else?  Yes, the Zope Storage Server then becomes a single point
  MM> of failure. The next stage of ZEO will be to replicate the ZSS
  MM> piece.
  
  ...</quote>

Zope Corp's Zope Replication Service (ZRS) product address the
reliability of the storage server.  A very high-level summary is: ZRS
extends the ZEO architecture to ensure that every transaction written
to a primary storage is replicated to any number of secondary
storages.  These secondary storages can reside on different machines,
and even different networks, to guard against hardware and network
failures.  The data in a secondary storage is a logical copy of the
primary storage.  Updates are replicated asynchronously to maximize
performance and minimize data loss if the primary fails.

Feel free to send me private email if you want to know more about ZRS.

Jeremy