I noticed a strange behavior with the Yahoo Finance API quotes. After hours, when the LastTradePriceOnly should be constant, I get toggling values when I reissue the request.
i.e. I get 4.27 for the first 2 trials, then I get 4.20 on the next and then 4.27 again. It toggles back and forth between those two values (4.27 being the 'correct' one that also shows on the web page).
This applies to all Tickers, not just one and since this is a significant difference, it really renders the API more or less useless. I tried to google this and couldn't find anyone else complaining. I'm not posting any code since I can see the 2 JSONs being plain different when I refresh the browser with the same URL request, so it's clearly an issue on the Yahoo side.
btw. , it's weird that they name this LastTradePriceOnly, but that's the only metric that seems to reflect the correct value (also during the trading day)
Related
I have a Django server. The server loads a webpage with almost all static content but a few numbers must load from the database.
I'm thinking about performance/price; I can host my Django server on a fast server and render the page using Django templates. or I can host the server on a slower machine and make a static page that loads the few numbers using ajax and host the page cheaply somewhere else like github.io.
The latter choice will have most of the page load real quick and real cheap.
I was wondering what are the trade-offs ?
Whichever server you decide to hire, you should always think of reducing the server load - no matter how fast your server is. By reducing server load I mean only make your server do what is really required at the moment.
Let's learn something from the big players like Facebook, for instance
You log into your account and you see that you've got 5 notifications and 3 new messages plus a couple of photos and highly interesting statuses of your friends. Cool! You now click on the notifications icon to find out if that hot girl (forgive me if you're a girl :D) has added you to her friends list or not. As you click a big white <div> pops up AND you see nothing but a loading gif! The notifications do appear, but after a couple of seconds. Try doing it with a slow internet connection, and you get to adore the beauty of the loading gif for a lot more time.
So, what do you make of it?
Facebook only made it's server count the number of notifications and new messages, and displayed those numbers to you. Thus reducing server load. It only displayed the notifications to you when you wanted to see them. And to load the notifications, all it took was a minimal AJAX call in which only around 10 KB of data was transferred!
Facebook does it all the time and everywhere. Consider this: Robert Downey Jr. posts a photo of himself on his Facebook page. A little while later, you see that it has got 10k+ comments. You decide to read them and click the comments button. An attractive loading gif pops up again for a little while and is soon replaced by comments. But hey, only 10 comments were loaded. What the ... Oh wait! That's how Facebook reduces its server load - read those 10 comments first, if you want to read more, send a request again.
Twitter does it too - the infinite scroll.
Icing on the cake
This approach benefits you in two ways:
It reduces server load - less chances of crashing a website.
It decreases your website's page-load time since you'll be passing less data i.e. the data required at that moment. Thus making your website faster. (Yes, it can outrun Flash, too!)
Food for thought
If you've got some cool technologies around such as AJAX, why not use it? Your server is not a donkey, for God's sake!
P.S. By Facebook and Twitter, I mean the engineers behind them.
Well It would depend on the following:
A. Whether you want to Display that number on Page load itself or when user clicks to see it* ?
If you want to show the the numbers at the time of Page load Itself than it is preferable to get them at time of Template response itself.
Why do you would want your Site Visitors to wait till those numbers populate (if the intention is to display them) ?
If it is to be displayed on User's click only then Ajax should be preferred
B. How much Time is this Query going to take and Can the query be optimized to minimal time ?
If the Query you are making takes a Lot of time than first effort should be made to optimize that query to be as fast as possible,
If the query can give result in minimal time than it is futile to do another Request to Server via Ajax.
But if you know the Query will take a lot of Time than Ajax is fine.
Sometimes, I request a page and it takes too long to receive a response for the request and then load the page (sometimes the request times out and I never get a response).
However, if I open a new tab, copy the exact URL, and then append it with an arbitrary GET variable (with an arbitrary value), the request gets a response very fast (as the normal state is) and the page then loads, although the request wasn't getting a response without that arbitrary GET variable.
For a fake example, if I request:
http://example.com/
It might take a long time just loading, not receiving any response yet, but if I just open a new tab (at the same time), and request:
http://example.com/?foo=bar
It loads like magic!
Why is that happening to me? what could be the reason along the road between my browser and the page's server? does that have any relevance to ISP servers caching?
Any explanation is much, much appreciated, as I really am eager to know the reason!
P.S: I'm in Syria (where anything crazy is possible in Internet network), and this doesn't happen only to me, but to all people I know.
EDIT:
Note that it happens even if a URL has a GET variable already, for a real example I have a blog, and sometimes requesting this page (I changed the domain):
http://myblogdomain.com/wp-admin/admin.php?page=jetpack
Takes too long time (and sometimes it times out), but if I open a new tab and request:
http://myblogdomain.com/wp-admin/admin.php?page=jetpack&foo=bar
It loads fast (as normal).
It's likely that there is a caching proxy and/or firewall between you and the rest of the internet. There is probably a rule in the proxy that says URLs with GET parameters can pass through since they are likely to return unique content, but URL's without parameters must be fetched through a cache. The cache is likely overloaded or broken.
You probably have a proxy that needs to do some lengthy process (content check, DNS lookup, etc) once per domain.
When you open the second tab, that length process would have already started (for the first tab), so it wouldn't take as long.
If this is the case, opening the first tab with a querystring and the second tab without would still result in the second tab loading faster.
1-form a web developer perspective :
to get more details about what is taking this time , i could the network tab of my best friend (firebug )
as you may see above , i can see how much time spent on each step on the page .
2-even though i think this question should be moved to https://serverfault.com/ to get answers form networks geeks
I have been trying to research the hack proposed by Avinash Kaushik in his book Web Analytics 2.0. He poses the problem whereby most web analytics tools are unable to record the time a user spent on the last page they visit on a website, or on the only page they visit. In other words if user comes to page 1, a timestamp is created showing the time they arrived at the page, when they visit page 2, a second timestamp is created. The time spent on page 1 can be calculated by timestamp 2 - timestamp 1. However if the user closes the browser window or navigates away from the website there is no way to record time on page 2. Here is a link to this problem on Kaushik.net
standard-metrics-revisited-time-on-page-and-time-on-site
One proposed hack is to use the window.onbeforeunload event to call a method and push the time that the page was unloaded to google analytics. So I tried the following code -
window.onbeforeunload = capturePageExit;
function capturePageExit()
{
_gaq.push(['_trackPageview', '/page-exit?page=' + document.location.pathname + document.location.search + '&from=' + document.referrer]);
return("You are about to close this page");
}
Using firebug I can see that the correct __utm.gif image is requested and the correct params are sent to google analytics. But clearly there is a problem now that this will be called on each page unload and so each visitor will appear to go from page1 -> page-exit -> page2 -> page-exit -> page3 -> page-exit... but I should get a more accurate time on site reading, right?
However this is at the expense of accurate navigation-summary data and so not a good solution. What would be good is if I could tell - if user has clicked the close browser/tab button or is navigating away from my site then record the page-exit.
I cant find a great deal of information about how to solve this problem, plenty of discussion about being aware of this inaccuracy when interpreting google analytics (and most web analytics tools probably), another useful link is time_on_page_and_time_on_site_how_confident_are_you
Just wanted to raise this on stackoverflow as I cant find a similar question and start a discussion about this, but my interpretation is that there isnt really a way around this problem but it is just better to be aware of it.
any thoughts?
------------------------------------------------------ UPDATE -----------------------------------------------------
Here is another link that was suggested to me from a blog called Savio.no, is this a good method?
how-to-measure-true-time-with-google-analytics
Web Analytics is not an exact science. Data is always approximate and most of the time sampled.
Web Analytics tools strive for Precision not accuracy. This whitepaper describes why it's more important to have precision and less important to have accuracy when working with Web Analytics.
Once you understand the difference between precision and accuracy and why it matters you will understand that it's not important to get the exact time on site metric, but a precise measure that could clearly express trendings or changes to that metric.
On other words forget about absolute numbers, learn to report using trends and changes.
Another advice, don't bother tweaking GA to render every single metric perfectly if you're never gonna use it. Bother with metrics that you can use. And by use I mean Actionable analysis.
There are, however a few cases were some code tweaking can help you out measuring the time on site. A clear example is a weblog. You may want to implement something like that in a weblog, ince most of your visits will be looking at your homepage, reading your posts and then leaving, all that is done in the same single PageView so it may be a good idea to fire an event when the user leaves to get the correct time on site, or maybe fire an event when the user scrolls past some threshold, in the end you'll be measuring the same ting, if the user scrolls more he reads more, and if the user spends more time then he reads more. So it may not make sense to track those 2 metrics to measure the same effect. Just choose one and stick with it, leave it running for a while to create historical data and then make use of it.
I'm building a Twitter app that requires to check user data somewhat frequently, but I'm facing trouble with a cache that's oddly on Twitter's side, not mine.
Try the following user:
users/show in XML: http://twitter.com/users/show.xml?screen_name=technolocus
users/show in JSON: http://twitter.com/users/show.json?screen_name=technolocus
normal page: http://twitter.com/technolocus
All these methods of accessing data should return the same values, right? Check the statuses_count for each of them.
XML: 12548
JSON: 12513
normal: 12498
The normal method (i.e. just visiting the profile non-programatically) serves up the most correct value of 12498. If I post or delete tweets to this account, it gets updated on the profile page instantly, but the XML and JSON methods still return cached data.
At this point, the values of the XML and JSON methods are 12 to 18 hours old respectively.
I first tried to access these methods from my website (hosted on Dreamhost). I thought it was Dreamhost caching the responses. Then I tried to access the API directly from my browser. I did a cURL from the command line from my machine after that. It wasn't dreamhost. I thought it was probably my ISP (I think they use NetApp or something like that). Then I asked a friend in another corner of India to try it. He's getting the exact same cached responses as I am.
So it isn't Dreamhost's cache; it isn't my ISP or my country's cache. There's only one conclusion - Twitter is caching responses.
How in the heavens do I get around this?!?
Forgot to mention this: The script on the server is in PHP and is using cURL to retrieve the XML and JSON data from Twitter, while the local tests have been just using the browser. Both have the exact same result!
First, I think you should report this a a bug to Twitter. I see the same discrepancy as you, and no matter what that seems like a bug. Even if they're caching, I'd expect that a cache on their side would store an abstract form that would then be rendered into HTML, JSON, and XML. I wonder if what's actually going on is that these requests are performing similar but different queries.
Are you sure that the values are "old"? For example, did you actually delete about 50 updates recently (since you say the HTML one is newest but shows a lower count than the other two)? If you create another update do you see the HTML number increment while the other numbers stay the same, or do they all increment simultaneously?
If what you are saying is accurate, and it probably is, generally, you can't get around it. Twitter would want to be caching its responses since they are costly to reproduce every single time.
When you use Twitter's APIs, you end up being bound by its conventions, even if that includes caching.
Your best bet is to tweet to #twitterapi and get them to give you a response as to why the two representations are divergent.
Add ?blah=xxxx to all urls.
I don't develop anything against twitter and ocassionaly manually "follow" three tweets by going to them in my browser. They always lag behind by half a day. I add ?asdsadsadsad to the url (everytime something different) and it always updates. I don't know what Twitter is doing here and came here while searching for the problem. But I guess this trick of appending a random value to the url via GET will probably work for your api requests, too.
I'm interested in finding out why this is used on some Web sites for processing user-initiated search submissions, how it affects the request and response flow, and programmatically why it would be necessary (or beneficial). In an MVC framework it seems difficult to execute since you are injecting another page into the middle of the flow.
EDIT:
Not advertising related. For instance, most travel sites used to do this, and there were no ads... some banking sites do it too, where there is just a loader that says something like "Please wait while we process your transaction...".
It is often used in long running requests to prevent the web server from timing out the request. With an interstitial page, you are able to continuously refresh the page until you get results back.
EDIT:
Also, for long running requests, it is beneficial to have a "Loading.." page in order to show the user that something is happening. Without the interstitial page, the request can appear to have hung up if it takes too long.
To supplement what HVS said, interstitials which appear before, say a homepage loads, are very much there for the purpose of advertising, we've all seen the 'close this ad' link.
One instance where they can be helpful from a user experience point of view is when a user initiates an action which requires feedback from a process which may take some time to respond - either because it's slow, busy or just has a lot of processing to do.
Think of a site where you book a flight online for example. You often get an interstitial on hitting 'find flights' because the the system is having to go off and ask for all relevant flight information and then sort them for you before displaying them on your screen. If this round-trip of 'request, interrogate, return, display' is likely to take an amount of time beyond that which a normal webpage transitions from one to the next, a UXDesigner may consider an interstitial screen (or message) to let the user know something is happening whilst at the same time allowing the system the time it needs to complete the request. Any screen with this sort of face-time is going to get the attention of your marketing department from a 'well while we've got them we might as well show them something' point of view.
As a UX Designer myself interstitials like this are not always preferred as I'd love every system to return data immediately but if it can't for whatever reason, I'm very much for keeping the user in the loop as much as possible about what is happening - rather than leaving them to stare at the browser status bar until they either try again or get fed up and leave.
One final point when considering this is also to have a lower and upper time limit on a screen like this. If you need to show an interstitial, show it for long enough so people can read it and understand it but not too long that they get fed up of waiting. As a rough guide, leave it open for at least 3-4 seconds (even if the process averages 4 seconds but has finished after 1 on this occasion). Between 4 and 10 seconds check every second to see if the process has responded (and then take the user to the next page f it has) and after 10 seconds seriously consider telling the user to either try again or telling them you've failed (whilst at the same time getting your tech team to fix what is ultimately a problem which will affect your bottom line).
I believe the vast majority of interstitial pages are there to run advertising.