\label{Caching}
LON-CAPA does not serve static web pages, but generates pages and other 
resources dynamically and adaptively based on a large number of data input
sources, such as the user preference, the course environment, maps, etc.

Since LON-CAPA also has to sustain large workloads, it is 
prohibitive to gather, compile, and process these data for every single
access, when in the vast majority of cases, nothing has changed between the
current and previous requests.

LON-CAPA thus caches data. There are basically two different 
\textbf{caching mechanisms\index{caching mechanisms}}, which LON-CAPA uses:

\begin{itemize}
\item Caching at \textbf{course initialization\index{course initialization}}:
Several sources of data are compiled when a user enters a course during a 
session. An example is the table of contents (DOCS/NAV) for the course - 
if you change DOCS, you need
to re-enter (``\textbf{re-initialize}'') the course in order to see the 
effects.

The course environment (PARM/Course Environment) in general also only gets 
evaluated when entering a course, and while it does get re-evaluated for your
session whenever you change anything, it - like DOCS changes - will not 
immediately take effect for
other users currently working in the course. So if for example you disable
course discussion, users will only be prevented from discussion when they 
enter the course the next time. 

\item Caching of \textbf{assessment parameters\index{assessment parameters}}:
Data such as the deadline of homework problems, and the text of Simple 
Problems, is only re-read \textbf{every ten minutes}. It can thus happen that
you open up a homework problem in PARM, but for another ten minutes, some 
students cannot access it. Also changes to Simple Problems will not immediately
take effect for all users (including yourself).
\end{itemize}
 
It is important to be aware of these mechanisms, since otherwise results can
be confusing (``Didn't I just change this???'').