I am using a webapp2 in GAE, when I called self.redirect to some page like below:
self.redirect(some_url)
which returned a page looks like cached, I have to refresh/reload the page so that I would get latest data.
Is there any cache setting for webapp2? or I have to set some properties for response of that page? Please advise.
In my project I've fixed that by adding time.sleep(0.1) just before the self.redirect('someurl') call.
Not sure if it is a best way to solve the problem, but pages started to show most recent info.
Edit: beware of consistency issue
Check out #Lindsay answer. Using time.sleep(0.1) might give you the expected result in a local environment, but you cannot trust it in a production environment. If you really need results to be strongly consistent, use an ancestor query, not time.sleep(0.1).
My guess is that this is happening because the earlier page is updating an entity that is then being accessed on the later page by means of a non-ancestor query. A non-ancestor query provides eventual-consistency rather than strong-consistency, so the problem is not that the page isn't being refreshed, but that it's showing what the data looked like before the update was completed. When you refresh, or add a call to time.sleep(), you may be providing enough time for the datastore to catch up, especially during testing. However, in production, your sleep may not be long enough in all cases, and the same is true of a page-refresh.
If you check your application and find out that you are using a non-ancestor query, and therefore your problem is indeed eventual-consistency vs strong-consistency, a Google search will show you that many pages discuss that topic; here's one: https://cloud.google.com/developers/articles/balancing-strong-and-eventual-consistency-with-google-cloud-datastore#ftnt_ref1.
The simplest solution seems to be to create an entity group and use an ancestor query, though that comes with a possible performance hit and a limitation of one update per second per entity group.
Got the same problem I have done a trick which is not good but helped me anyway. Called a temporary view file then did html redirect:
<meta http-equiv="refresh" content="0.5;URL='/'">
Hope it helps. any one with a better answer?
Do you call return immediately after the self.redirect(some_url)? It may be falling through to other code that renders a page.
Related
I have to mock up a ticking dashboard which is part of a proposal. I am looking for ideas other than the HTTP Refresh option that I am thinking of. The objective is to quickly mock up a look and feel and a working dashboard that ticks over. It only had to provide new content every five seconds. EG there are a bunch of KPI's and their outputs which are percentages have to be updated..
A simple bunch of HTML pages using HTTP Refresh is on my mind. Is there a better option anyoine can think of. EG can HTML5 do this better? Is CSS an option? Thank you in advance for any ideas
I would be going for an ajax call back to the server to get the latest update and then embed that wherever it needs to go - you could set the ajax function on a timer to run every 5 seconds or 1 second or whatever. This way your entire page is not being refreshed, and additionally you can be calling back to the server for a new update even while the previous on is still being rendered.
Downside is that you won't have a page history (i.e. the users will not be able to navigate 'back' to previous ajax updates) unless you explicitly create one; I can't see that being necessary though.
Please post a comment if you need more info about ajax.
Currently reading Bloch's Effective Java (2nd Edition) and he makes a point to state, in bold, that overusing POSTs in web applications is inherently bad. Unfortunately, he doesn't specify why.
This startled me, because when I do any web development, all I ever use are POSTs! I have always steered clear of GETs for security reasons and because it felt more professional (long, unsightly URLs always bother me for some reason).
Are there performance differentials between GET and POST? Can anyone elaborate on why overusing POSTs is bad, and why? My understanding - and preliminary searches - seem to all indicate that these two are handles very similarly by the web server. Thanks in advance!
You should use HTTP as it's supposed to be used.
GET should be used for idempotent, read queries (i.e. view an item, search for a product, etc.).
POST should be used for create, delete or update requests (i.e. delete an item, update a profile, etc.)
GET allows refreshing the page, bookmark it, send the URL to someone. POST doesn't allow that. A useful pattern is post/redirect/get (AKA redirect after post).
Note that, except for long search forms, GET URLs should be short. They should usually look like http://www.foo.com/app/product/view?productId=1245, or even http://www.foo.com/app/product/view/1245
You should almost always use GET when requesting content. Only use POST when you are either:
Transmitting sensitive information which should not appear in the URL bar, or
Changing the state on the server (adding/changing/deleting stuff, altough recently some web applications use POST to change, PUT to add and DELETE to delete.)
Here's the difference: If you want to give the link to the page to a friend, or save it somewhere, or even only add it to your bookmarks, you need the full URL of the page. Just like your address bar should say http://stackoverflow.com/questions/7810876/abusing-http-post at the moment. You can Ctrl-C that. You can save that. Enter that link again, you're back at this page.
Now when you use any action other than GET, there is simply no URL to copy. It's like your browser would say you are at http://stackoverflow.com/question. You can't copy that. You can't bookmark that. Besides, if you would try to reload this page, your browser would ask you whether you want to send the data again, which is rather confusing for the non-tech-savy users of your page. And annoying for the entire rest.
However, you should use POST/PUT when transferring data. URL's can only be so long. You can't transmit an entire blog post in an URL. Also, if you reload such a page, You'll almost certainly double-post, because the above described message does not appear.
GET and POST are very different. Choose the right one for the job.
If you are using POST for security reasons, I might drop a mention of other security factors here. You need to ensure that you send the data from a form submit in encrypted form even if you are using POST.
As for the difference between GET and POST, it is as simple as GET is used to send a GET request. So, you would want to get data from a page and act upon it and that is the end of everything.
POST on the other hand, is used to POST data to the application. I am talking about transactions here (complete create, update or delete operations).
If you have a sensitive application that takes, say and ID to delete a user. You would not want to use GET for it because in that case, a witty user may raise mayhem simply changing the ID at the end of the URL and deleting all random uses.
POST allows more data and can be hacked to send streams of files as well. GET has a limited size though.
There is hardly any tradeoff in using GET or POST.
There are a number of different websites that let you monitor specifi web pages for any changes, such as watchthatpage.com or page2rss.com
I'm interested in the way how those sites are working, meaning how do they determine whether some web page is updated. Do they just copy all the text from the page, store it in memory and compare it later to the content of a site's page?
Or maybe they look for some specific html elements and compare theirs values?
Please help me to find the answer.
How it works: http://www.watchthatpage.com/information.jsp
I suspect that they store the entire contents, and every time they check, they compare. If different, send alert, otherwise don't.
There's two ways this can be done just off the top of my head.
The first is to pull the HTML and do a simple string.compare.
The second way, would be to do a HEAD request See, section 9.4 here
I have an asp.net C# .net 3.5 page which contains several user controls. I am noticing that sometimes the html loaded on the browser is incomplete. It seems to get cut-off.
Any suggestions on how to troubleshoot whats the root cause?
This can be symptomatic of server errors or proxy problems. I would use Fiddler to check what's going back and forth between your browser and the server. If you are getting any 500 (server error) response codes, that would be a good place to look.
Another thing to check would be javascript errors on the page, because depending on what your javascripts are doing, errors can prevent loading of other content in some cases.
womp probably has most of the bases covered, but the other angle that can lead to issues like this would be exceptions getting eaten but causing processing to stop, thereby sending half the page or somesuch.
Verify that your HTML is being written to the page by viewing the source code of the page after it loads. My guess is that the HTML that is being output is invalid, and that the browser isn't able to properly display it. Make sure all your HTML tags are properly closed and balanced.
It could also be an issue with the request being ended midway through. Try removing one control at a time from the page and see if the situation improves. If it does, you'll know which control is to blame.
It is quite unlikely that it is the same problem, but I had that happen before where the page had a custom filter attached to response.filter which reformatted the output to fix up some dotnet SEO problems. And the one we wrote had a bug where one regular expression consumed a bit too much copy in some instances and broke the output
I'm trying to run a multivariate test across 3 pages, google says this should be ok, as long as you use the same section names, it doesn't care about the url so much.
so I have checked in google optimizer, it says all my scripts are set up correctly.
Also the strange thing is it DOES work, it replaces the content, but it never ever saves a cookie, so when you get to the next page, or even just refresh the same page, you might get a different variant.. Which obviously shouldn't happen.
I'm pulling my hair our here, any help would be appreciated.
I had the exact same problem. I've run several tests with GWO and never had this issue. However, with my latest MVT, at first I wasn't seeing GWO even set the cookie. Then, it started setting the cookie but was not able to read the cookie.
Although I am running a sitewide, MVT, I am not running it across multiple domains. However, in order to get GWO to set and read the cookie correctly, I found that I needed to use some of the code required for sitewide tests that span multiple domains. Here is the google article on cross domain tracking:
http://www.google.com/support/websiteoptimizer/bin/answer.py?hl=en&answer=151978
According to the Google WSO API, by default, GWO is setting this property:
gwoTracker._setDomainName("auto");
For whatever reason, it was my experience that this was not happening and by making this call explicitly in my code, it fixed the problem! This call needs to be added to both your Tracking Script and your Conversion Script.
Again, I've never experienced this with any of my other GWO tests, so it was kind of weird to have it happen out of the blue but explicitly making this call fixed this problem for me. Good luck.