Home and out

[Sam I Am]

Brad whenever I hit home on this site it kicks me out and I have to re enter my name etc. Is this supposed to happen or is this an aging iPad issue? 

[bradl]

Glad you posted this because I have noticed the same on my iPad as well. 

Short answer: just "reload" the page.

You are not actually logged out when you go back, the device is just showing you a copy of the page from when you last visited it, which was in a logged-out state. If you refresh the page you force the device to contact the server again, which will send you the page that a logged-in user should see.

Mobile devices can be very aggressive about caching (saving) pages. They do it to increase the apparent load speed of the page and to reduce cellular bandwidth use.

It can also happen with desktop browsers depending on the browser, your service provider etc. It is however much rarer on desktops since they are presumed to have less restrictive download quotas.

[bradl]

You may wonder why "clear your cache" is almost always the first step in troubleshooting any problem on a web site.

Here are some boring notes about only a few of the types of  "caching" which affect many aspects of using a dynamic database-driven site like ours, where each page view is custom assembled for the viewer. Every page may have to account for factors like logged-in or guest, member group type, individual member preference settings, and so on.

Software Caching

Whenever you fetch a page to load, before the server can send it to your browser for display the software itself performs many (dozens or even scores) of database queries to gather up and assemble all the bits to create the exact page you requested.

Most pages are a mix of static (unchanging) and dynamic (changing) content. At the top of the page where I see "Hello bradl" you will see your own name. That is dynamic content. Elsewhere on the page there may be content that never or rarely changes. For example the name of the site. That static content can be stored and reused without checking for updates pretty safely. Thing like the most recent topics list require queries to find out what has been posted and when, how does the timestamp compare to previous content (has it changed) and has the person loading the page seen it yet? This is also dynamic content.

All these queries put a load on the server and if there are many people on the site at once (including robots and guests) things can bog down. To compromise on being both dynamic but also responsive, the software will cache certain bits, for varying lengths of time. Most of the dynamic blocks of content are cached for around five minutes while others can be cached for weeks or months. That means if the server has shown you (an in some cases, shown anyone) that block once already, it doesn't bother recreating the block for display, it just sends a copy of the block of content from the last time it was assembled. If enough time has passed it knows the information may be stale and will recreate it from scratch again. Some blocks are not cached at all. 

Browser Caching

Your browser is trying to help you load pages quickly and get to the good stuff faster. When a browser fetches a page it has to do *a lot* of work interpreting all the markup and display-related code the server sends about how the page is put together. The server sends the blueprint and the parts but your browser has to assemble and display the darned thing. 

If the requested page includes a photo called toocute.png the browser will load all the bits that form the picture as saved on the server, but also need to know what size the server intended it to be when displayed. Further your browser may make adjustments depending on how your personal browser is set up: do you have your window shrunk down to be tall and narrow or short and wide? Are you on a super-high resolution device? Are you on a mobile? Your browser will do some calculations to show the photo as best it can.  

In order to show you that page at all, the browser puts a temporary copy of  the page content on your local device. It's saved in a temporary file area (called, no surprise, the cache). The next time the browser is asked to show a page, it may check all the "assets" or bits of the page it is being asked to fetch and check in the cache to see if maybe there's already a copy laying around. Oh hey, look I already have a copy of  toocute.png.  The browser may "decide" that since there is already a copy of toocute.png right here in the local files it can just insert that in the correct place in the new page and save you lots of time waiting for information it already has on hand locally to pointlessly download yet again from a distant server. 

There a methods to tell browsers how old information can be before they check for new information or to force them to check every time, but there are many many browsers and many many servers and pages are coded with varying degrees of compliance to standards so it is not surprising that caching occasionally has unintended effects.

Browser do *a lot* of work and are frankly amazing. Browser caching makes a lot of sense and it works pretty well. But occasionally they stubbornly serve old information when they should be fetching a new version. Clearing the cache clears the deck so everything can start fresh.

Service Provider Caching

While somewhat less of a problem than it used to be, your internet service provider may do some amount of information caching of its own, in the pipeline between our server and your device, to keep its own costs down and performance up. Certain providers used to be particularly egregious in this area but I think those days are long past. Still, you almost cannot know if some chunks of information delivered to your browser came directly from the server or from a copy that your ISP noticed it still had in its pipeline and decided to save you some time by delivering a stored copy.  I think this is pretty rare these days but I mention it as an example of Yet Another Cache Source.

Other

Believe it or not there are still more ways that content can be saved in intermediate stages in disparate places to be streamlined (inserted) into a page rendering in the interests of speed, server load balancing, redundancy, or other reasons. 

All this is just a long-winded way to confirm that indeed, clearing your browser cache (and sometimes deleting cookies as well) are often genuinely necessary step to resolving rendering and performance oddities on web sites. Here is a site that provides instructions for many types of browsers:

http://www.refreshyourcache.com/en/home/