caching

问题 I don't find get the practical difference between Cache-Control:no-store and Cache-Control:no-cache . As far as I know, no-store means that no cache device is allowed to cache that response. In the other hand, no-cache means that no cache device is allowed to serve a cached response without validate it first with the source. But what is that validation about? Conditional get? What if a response has no-cache , but it has no Last-Modified or ETag ? Regards. 回答1: But what is that check about?

问题 I have loaded in a R console different type of objects. I can remove them all using rm(list=ls()) or remove only the functions (but not the variables) using rm(list=lsf.str()) My question is: is there a way to remove all variables except the functions 回答1: Here's a one-liner that removes all objects except for functions: rm(list = setdiff(ls(), lsf.str())) It uses setdiff to find the subset of objects in the global environment (as returned by ls() ) that don't have mode function (as returned

问题 I am trying to figure out the fastest way to access data stored in a junction object. The example below is analagous to my problem, but with a different context, because the actual dataset I am dealing with is somewhat unintuitive in its relationships. We have 3 classes: User , Product , and Rating . User has a many-to-many relationship to Product with Rating as the junction/'through' class. The Rating object stores the answers to several questions which are integer ratings on a scale of 1-5

问题 I'm trying to use the WBINV instruction on linux to clear the processor's L1 cache. The following program compiles, but produces a segmentation fault when I try to run it. int main() {asm ("wbinvd"); return 1;} I'm using gcc 4.4.3 and run Linux kernel 2.6.32-33 on my x86 box. Processor info: Intel(R) Core(TM)2 Duo CPU T5270 @ 1.40GHz I built the program as follows: $ gcc $ ./a.out Segmentation Fault Can somebody tell me what I'm doing wrong? How do I get this to run? P.S: I'm running a few

问题 How do you implemented etags inside a PHP file? What do I upload to the server and what do I insert into my PHP file? 回答1: Create / edit your .htaccess file and add the following: FileETag MTime Size Either place the following inside a function or put it at the top of the PHP file that you need etags to work on: <?php $file = 'myfile.php'; $last_modified_time = filemtime($file); $etag = md5_file($file); header("Last-Modified: ".gmdate("D, d M Y H:i:s", $last_modified_time)." GMT"); header(

问题 I'm looking at the following apple example source code: /* Cache the formatter. Normally you would use one of the date formatter styles (such as NSDateFormatterShortStyle), but here we want a specific format that excludes seconds. */ static NSDateFormatter *dateFormatter = nil; if (dateFormatter == nil) { dateFormatter = [[NSDateFormatter alloc] init]; [dateFormatter setDateFormat:@"h:mm a"]; } Trying to figure out: Why use the static keyword? How this equates to a cached variable if you set

问题 For two subsequent requests, which of the following two headers is given more weight by browsers should one of them change: ETag or Last-Modified? 回答1: According to RFC 2616 section 13.3.4, an HTTP 1.1 Client MUST use the ETag in any cache-conditional requests, and if both an ETag and Last Modified are present, it SHOULD use both. The ETag header is considered a strong validator (see section 13.3.3), unless explicitly declared weak by the server, whereas the Last Modified header is considered

问题 is there a way in C++ to determine the CPU's cache size? i have an algorithm that processes a lot of data and i'd like to break this data down into chunks such that they fit into the cache. Is this possible? Can you give me any other hints on programming with cache-size in mind (especially in regard to multithreaded/multicore data processing)? Thanks! 回答1: According to "What every programmer should know about memory", by Ulrich Drepper you can do the following on Linux: Once we have a formula

问题 In the iPad project I'm working on I've got a UIWebView inside of the app which displays a .html file which links to a .css file, i.e. <link rel="stylesheet" href="style.css" type="text/css"> These files are stored locally on the iPad but are fetched from a remote server. I've noticed that UIWebView caches the .css file more or less indefinitely, and refuses to load the new file whenever I change it. I've once changed the name of the file just to get it to reset, but that's unacceptable in

问题 Is there any way to diable the caching of a single javascript file in my ASP.NET applicaiton without disabling the caching of any other files in the application? It is running on IIS 7 in Azure, so to me it seems that my only options of controlling this are within the webserver tags. I currently use the folowwing config, but this is disabling cache on all files. <modules runAllManagedModulesForAllRequests="true"/> <staticContent> <clientCache cacheControlMode="DisableCache"/> </staticContent>