Analysis of the principles of using client-side caching to optimize websites Page 1/2_PHP Tutorial

Many people first want to optimize the program from the server cache aspect. Many different server cache methods have their own characteristics. For example, in some projects I have participated in, I have used Com+/Enterprise Libiary Caching according to the cache hit rate. Server-side caching and HTTP Compression technology in Windows services, static files, etc., but client-side caching is often ignored by people. Even if the server’s cache makes your page access very fast, it still needs to rely on browser downloads. And output, and when you add client-side caching, it will bring you a lot of benefits. Because she can cache the most frequently accessed pages in the site, fully improving the throughput of the Web server (usually in terms of requests per second data computing) to improve application performance and scalability.
An online shopping survey shows that most people are willing to queue in stores, but are not willing to wait when shopping online. Websense research company claims that as many as 70% of Internet users are unwilling to read a page for more than 10 seconds. More than 70% of people will cancel their current order because the speed is too slow.


Basic knowledge
1) What is "Last-Modified"?

When the browser requests a URL for the first time, the return status from the server will be 200, The content is the resource you requested, and there is a Last-Modified attribute that marks the time when this file was last modified at the end of the service. The format is similar to this:

Last-Modified: Fri, 12 May 2006 18:53 :33 GMT

When the client requests this URL for the second time, according to the provisions of the HTTP protocol, the browser will send the If-Modified-Since header to the server to ask whether the file has been modified after this time:

If-Modified-Since: Fri, 12 May 2006 18:53:33 GMT

If the resource on the server side has not changed, it will automatically return HTTP 304 (Not Changed.) status code, the content is Empty, thus saving the amount of data to be transmitted. When the server-side code changes or the server is restarted, the resource is reissued and the return is similar to the first request. This ensures that resources are not sent to the client repeatedly, and also ensures that when the server changes, the client can get the latest resources.

2) What is "Etag"?

HTTP protocol specification defines ETag as "the entity value of the requested variable" (see - Chapter 14.19). Another way to put it is that an ETag is a token that can be associated with a Web resource. A typical web resource would be a web page, but it could also be a JSON or XML document. The server is solely responsible for determining what the token is and its meaning, and transmitting it to the client in the HTTP response header. The following is the format returned by the server:

ETag: "50b1c1d4f775c61:df3"

The query update format of the client is as follows:

If-None-Match: W/"50b1c1d4f775c61:df3"

If the ETag has not changed, status 304 will be returned and then not returned, which is also Same as Last-Modified. I tested Etag mainly to be useful during breakpoint downloads.


How do Last-Modified and Etags help improve performance?
Smart developers will use Last-Modified and ETags request http headers together, which can take advantage of the client (such as a browser) cache. Because the server generates the Last-Modified/Etag tag first, the server can use it later to determine whether the page has been modified. Essentially, the client is asking the server to validate its (client-side) cache by passing this token back to the server.
The process is as follows:
1. The client requests a page (A).
2. The server returns page A and adds a Last-Modified/ETag to A.
3. The client displays the page and caches the page together with Last-Modified/ETag.
4. The client requests page A again and passes the Last-Modified/ETag returned by the server in the last request to the server.
5. The server checks the Last-Modified or ETag and determines that the page has not been modified since the last client request, and directly returns response 304 and an empty response body.

The following example describes how to use server-side code to operate client-side caching:

http://www.bkjia.com/PHPjc/319427.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/319427.htmlTechArticleMany people first want to optimize the program from the server cache aspect. There are many different server cache methods. My own characteristics, like some projects I have participated in, according to the...