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Entry  25 Jan 2021, Thomas Lindner, Suggestion, mhttpd browser caching 
    Reply  25 Jan 2021, Stefan Ritt, Suggestion, mhttpd browser caching 
       Reply  25 Jan 2021, Thomas Lindner, Suggestion, mhttpd browser caching 
    Reply  08 Feb 2021, Konstantin Olchanski, Suggestion, mhttpd browser caching 
       Reply  08 Feb 2021, Stefan Ritt, Suggestion, mhttpd browser caching 
Message ID: 2081     Entry time: 25 Jan 2021     In reply to: 2080
Author: Thomas Lindner 
Topic: Suggestion 
Subject: mhttpd browser caching 
I tried reloading the pages.  If I reloaded the actual elog page

then it bypassed the cache and got the correct updated page from mhttpd.

However, if when I reloaded the status page

and then clicked the Elog button then I just got the cached (old) page.  Admittedly reloading the status page doesn't make so much sense (once I thought about it), but it is what I tried first (I'm good at modelling unexpected user behaviour); so there is some risk that the user will try reloading the wrong page and will be stuck not getting the external elog page (until 24 hours runs out).

Anyway, I will update the documentation to note that you need to reload the elog page after changing this variable.  That's probably an adequate solution.

I certainly don't suggest getting rid of caching entirely.  I was trying to think whether there was a set of pages where it would make sense to disable the cache (like the elog page).  But maybe that will just cause more problems.

> Let me first explain a bit why caching is there. Once we had the case that someone from 
> TRIUMF opened a midas custom page at T2K. It took about one minute (!) to load the page. 
> When we looked at it, we found that the custom page pulled about 100 items with individual
> HTTP requests from Japan, each taking about one second for the roundtrip. Then we redesigned
> the custom page communication so that many ODB entries could be retrieved in one operation,
> which improved the loading time from 100s to about 2s.
> With the buttons we will have to make the same compromise. If we do not cache anything,
> loading the midas status page over the Pacific takes many seconds. If we cache all, any
> change on the midas side will not be reflected on the web page. So there is a compromise
> to be made. I thought I designed it such that the side menu is cached locally, but when
> the user presses "reload", then the full menu is fetched from the server. Of course one
> has to remember this, so changing the ELOG URL or other things on the menu require a
> reload (or wait a certain time for the cache to expire). So try again if that's working
> for you. If not, I can visit it again and check if there is any bug.
> If we go the route to disable the cache, better try this to T2K and see what you get before
> we commit ourselves to that. Last time TRIUMF people were complaining a lot about long
> load times.
> Best,
> Stefan
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