[Modeling-cvs] SF.net SVN: modeling: [1003] trunk/ProjectModeling/Modeling/doc/UserGuide/FrameworkTypicalUsage.tex

[<sbi...@us...>]

Revision: 1003
Author:   sbigaret
Date:     2006-04-23 08:10:24 -0700 (Sun, 23 Apr 2006)
ViewCVS:  http://svn.sourceforge.net/modeling/?rev=1003&view=rev

Log Message:
-----------
Updated: doc. explicitly mention the problems of using ZECS w/ ZEO, and the solutions

Modified Paths:
--------------
    trunk/ProjectModeling/Modeling/doc/UserGuide/FrameworkTypicalUsage.tex
Modified: trunk/ProjectModeling/Modeling/doc/UserGuide/FrameworkTypicalUsage.tex
===================================================================
--- trunk/ProjectModeling/Modeling/doc/UserGuide/FrameworkTypicalUsage.tex	2006-04-23 13:01:38 UTC (rev 1002)
+++ trunk/ProjectModeling/Modeling/doc/UserGuide/FrameworkTypicalUsage.tex	2006-04-23 15:10:24 UTC (rev 1003)
@@ -238,23 +238,64 @@
 \label{fig:enable-bind-ec-txn-to-zope-txn}
 \end{figure}
 
-%% \begin{figure}
-%% \ifpdf
-%% \includegraphics[width=\textwidth]{./UserGuide/ZECS}
-%% \else
-%% \begin{htmlonly} % HTML
-%% \htmladdimg{ZECS}
-%% \end{htmlonly}
-%% \fi
-%% %begin{latexonly}
-%% \ifpdf% PDF
-%% \else%LATEX/dvi
-%% \fi
-%% %end{latexonly}
-%% \caption{Binding Zope txn to SESSION's defaultEC() txn}
-%% \label{fig:enable-bind-ec-txn-to-zope-txn}
-%% \end{figure}
+\subsection{ZEO\label{framework-integration-zope-zeo}}
 
+Projects using ZEO should take extra care before using the
+\module{ZEditingContextSessioning} (ZECS) product.
+
+In ZEO environments, different Zope processes are launched. The problem is
+that the ZECS product is designed to work in a MT environment, but it {\bf
+cannot} share EditingContexts between different processes.
+
+The fact is that, you cannot share EC between different processes (so
+this is not specific to zeo itself).  To do such a thing, it would be
+necessary to store the EC in the session along with its pending
+insertions/deletions, and the whole graph of objects as well since
+pending modifications can exist in-memory.  It is not possible in the
+current implementation, and there is no plan for making this available
+(for example, in the zope/zeo case, this means
+that every single object and their attributes should be made
+zodb-Persistent so that they can be stored in a session object).
+
+
+In fact, Zope/zeo \& {\sc zodb} address the same problem by opening/ closing a
+transaction at the beginning/end of each request loop. In this situation, if
+you need to hold back changes between two or three requests/pages, you won't
+change the real object in the "main" zodb, rather you'll store the changes in
+a session object.
+
+ZECS faces the same problem.  Here are the options you have, in this case:
+
+\begin{itemize}
+\item If every changes made in a request loop is committed/rolled back at the
+      end of the request, then you'll made changes directly in the object.
+      You can do the same w/ ZECS: this is why it has an option binding
+      EC-transactions to zope transactions,
+      cf.~\ref{framework-integration-zope-options}.
+
+\item on the other hand, if the modifications of, say, a given objet should be
+      made accross different requests/pages before being permanently stored in
+      a db (either zodb, or rdbms), you'll just make it the usual way; e.g.
+      storing the changes in a session-object, then in the last page,
+      committing the changes into the object and the DB.
+
+\end{itemize}
+
+A third solution is possible, where you can use the ZECS even in
+ZEO environment.  EditingContext cannot be shared accross
+processes, but if you can make sure that a given session is always
+served by the same zeoclient, then you'll get back the "full power" of
+having a session-EC, with pending (uncommitted) changes crossing the
+page requests.
+
+\paragraph*{Using Pound}~\\
+
+\ulink{Pound}{http://www.apsis.ch/pound/} is a load balancer that can
+distribute the load among several Zope servers running on top of ZEO.  Since
+it has a feature that allows to redirect requests to a zeoclient on per
+session basis (by IP or user), you can use it to solve the problem of using
+ZECS in a ZEO environment.  To enable this feature: TODO
+
 %%
 \section{Others\label{framework-integration-others}}
 


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