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Help on caching to avoid confusion.

    1: \label{Caching}
    2: LON-CAPA does not serve static web pages, but generates pages and other 
    3: resources dynamically and adaptively based on a large number of data input
    4: sources, such as the user preference, the course environment, maps, etc.
    5: 
    6: Since LON-CAPA also has to sustain large workloads, it is 
    7: prohibitive to gather, compile, and process these data for every single
    8: access, when in the vast majority of cases, nothing has changed between the
    9: current and previous requests.
   10: 
   11: LON-CAPA thus caches data. There are basically two different 
   12: \textbf{caching mechanisms\index{caching mechanisms}}, which LON-CAPA uses:
   13: 
   14: \begin{itemize}
   15: \item Caching at \textbf{course initialization\index{course initialization}}:
   16: Several sources of data are compiled when a user enters a course during a 
   17: session. An example is the table of contents (DOCS/NAV) for the course - 
   18: if you change DOCS, you need
   19: to re-enter (``\textbf{re-initialize}'') the course in order to see the 
   20: effects.
   21: 
   22: The course environment (PARM/Course Environment) in general also only gets 
   23: evaluated when entering a course, and while it does get re-evaluated for your
   24: session whenever you change anything, it - like DOCS changes - will not 
   25: immediately take effect for
   26: other users currently working in the course. So if for example you disable
   27: course discussion, users will only be prevented from discussion when they 
   28: enter the course the next time. 
   29: 
   30: \item Caching of \textbf{assessment parameters\index{assessment parameters}}:
   31: Data such as the deadline of homework problems, and the text of Simple 
   32: Problems, is only re-read \textbf{every ten minutes}. It can thus happen that
   33: you open up a homework problem in PARM, but for another ten minutes, some 
   34: students cannot access it. Also changes to Simple Problems will not immediately
   35: take effect for all users (including yourself).
   36: \end{itemize}
   37:  
   38: It is important to be aware of these mechanisms, since otherwise results can
   39: be confusing (``Didn't I just change this???'').