I have a very basic doubt about caching. I have sent a request to an aspx page from browser. Since it is an http Get request by default it will be cached. I can see that in about:cache of browser. But if that page is cached, then how my modification (may be in css or js of that particular aspx page) is reflecting on next request. That means it is not taking that from cache?
But At that time cache expire shows something like this "1970-01-01 05:30:00" in about:cache of that aspx request. All other static pages (external js) it is showing future expiry date.
Does a "past expiry" date simply imply that the item should not be "fetched again" from cache?
If enabled Output caching I know the new modification will not see as long as the cache is not expired. But then how this asp.net output cache and http get by default caching mechanism differs? I know Output caching has the facility to cache it in server or proxy, so it will serve for multiple users. But at the browser level how it differs?
Btw I got the answer :)
http://devproconnections.com/aspnet/aspnet-pages-and-browser-caching
Thanks again.
Related
I have set content caching on a specific folder by following the local web.config method. I don't think it works, and I would like to fix this.
I activate the cache using the IIS / HTTP Headers / Common headers feature. I set them to 1 day of expiration.
I opened a page with Google Chrome in private navigation, and then open the Network tab in the console.
The first time I load the page, everything loads from the site, obviously.
If I refresh the page, I see 2 types of loading in the Network console:
the files from Google and Facebook and such have a status of 200, and a size of (from cache).
the files from the folder for which I set the caching have a status of 304 and their size is displayed.
So, I guess the caching setting doesn't work? Or does the 304 response means that it's loaded from the cache? If they aren't, how can I make it work ?
Thanks !
304 is a way of caching. The server says that the content of the resource hasn't changed and it doesn't have to send the response content (the response content is empty).
This is quite convenient. The browser still makes the request for the resource (so that when it changes the new content is delivered to the client) but the server possibly saves the bandwidth by sending 304 + empty body instead of 200 and body content.
As I understand, this is how browser caching works. Assuming, a far future header has been set to let's say a year and foo.js is set to be cached. Here are some scenarios:
First visit to the page, server returns 200 and foo.js is cached for a year.
Next visit, browser checks the cache but has to check the server if foo.js has been modified. If not, server returns a 304 - Not Modified.
User is already on the page (and foo.js is in cache) clicks a link to go to another page, browser looks at the cached version of foo.js and serves it without doing a roundtrip to the server and returns a 200 (Cached).
User is already on the page (and foo.js is in cache) and for some reason hits F5/Reload, browser checks the cache but has to do a round trip to the server and check if foo.js has been modified. If not, server returns a 304.
As you can see, whenever a page is refreshed, it will always have to do a trip to the server to check if the file has been modified or not. I know this is not a lot and server will only return the header info but a round trip time in some cases are extremely important.
The question is, is there a way I can avoid this since I'm already setting the expiration for the files. I just want it to always fetch it from the cache until the expiration has expired or replace the file with something else (by versioning it).
From what I understand, pressing F5/Ctrl-R is browser specific action, thus leaving the control to browser.
What if the user clears the cache before clicking another action? So, even if there was HTTP specification to forcefully use cache in F5, there's no guarantee that you'll be able to achieve your need.
Simply configure and code to cache wherever maximum possible and leave the rest to user.
It looks like, when you navigate to a page (that is entering an address in URL bar or clicking a link), resources are fetched from cache without a HEAD request to server. But when you refresh the page it does the HEAD request ans so the RTT.
This looks more clear in Network tab of IE's Developer Tools. If you see the initator column, it says navigate for the first case and refresh for CTRL+R or F5.
You can override the F5 and CTRL+R behavior by adding an event listener on them and doing a window.location = window.location and prevent the default behavior by event.peventDefault or something similar. This will cause page navigation instead of refresh.
Also, I didn't test the case when the cached resource has actually changed on server. If that turns out to be a problem, you can solve it by version numbering of resources and generation of HTML with URLs pointing to the latest version of the resource (kind of like cache-manifest problem with HTML5 offline applications).
EDIT: This however doesn't solve the problem if user clicks on browser's refresh button; onbeforeunload event may help in that case.
I am working on a new website. While testing some of the functionality I had a number of debug statements and was watching the logs. It seems that Firefox (at least) loads the "next" page in the menu as well as the page I have clicked on. If I have menu items A B C D E and click on B then I see a request for mysite.com/B and then a request for mysite.com/C in the logs, and so on.
Is this some kind of look-ahead performance thing? Is there any way to avoid it (setting an attribute on the link maybe?) The problem is that the second page in my menu is somewhat heavier as it loads a whole lot of data from a web service. I'm happy for people to do that if they want to use the functionality, but would rather not that every visitor to the front page loads it unneccessarily. Is this behvaiour consistent across browser?
Yes, Firefox will prefetch links to improve the perceived performance to the user. You can read more about the functionality in Firefox here https://developer.mozilla.org/en-US/docs/Link_prefetching_FAQ
It isn't possible to disable this in the client's browser, however the request should include the header X-moz: prefetch which you can use to determine if it is in fact a prefetch request or not, and potentially return a blank page for prefetch requests. You can then use Cache-control: must-revalidate to make sure the page loads appropriately when actually requested by the user.
If you happen to be using Worpdress for your site, you can disable the tags with the prefetch information by using:
Wordpress 3.0+
//remove auto loading rel=next post link in header
remove_action('wp_head', 'adjacent_posts_rel_link_wp_head');
Older versions:
//remove auto loading rel=next post link in header
remove_action('wp_head', 'adjacent_posts_rel_link');
Yes, it's called prefetch. It can be turned off in the client, see the FAQ:
https://developer.mozilla.org/en-US/docs/Link_prefetching_FAQ
I'm not aware of a way to turn it off via the server
I am having an issue with IE8 and its caching behaviour.
If I hit the page index.html and then continue to hit it again I am servered a page from the server.
However if I hit the page index.html?ui=v2 then index.html then index.html?ui=v2 I am served the page from cache.
The problem is the querystring ui=v2 is used to set a cookie which dtermines the view to deliver. As the page comes from cache the cookies view mode is not updated and I am served the same content as displayed for index.html (with no querystring).
This is IE8 and below, no other browsers.
Keen for any input Ideally I do not want to update the meta or response headers.
Thanks in advancecokkies
How can I use Fiddler to confirm that HTTP caching is working? Is there another better way?
You can confirm caching by having a page fetch a resource and note that no request for the resource appeared in Fiddler. I can't think of a better way to do it. Works for me.
right click the URL in the fiddler and click properties, you can check the cach info in that popup under "WININET CACHE INFO"
Browse the site through the Fiddler as proxy. In each response details, there's a tab "Caching". This shows useful info about the response headers - e.g. what the different Cache-Control and Expires values mean.
I think the best way is to use the method demonstrated within most caching tutorials - Have a label on the page that displays the current server time. If the value is cached, you will not see it update with subsequent page refreshes until the cache is regenerated.
If your requirement is more complex (you need to use Fiddler), Anthony's suggestion is the one I have used successfully in the past.
Fiddler will definitely help with this. You'll either see the server respond with an HTTP 304 response (Not Modified - which tells the client that the cached item is still valid) or for content that has it's web expiry set correctly, you won't see a request at all.
In fact, you'll find Firefox plus FireBug will do this for you too.