In most cases our website will use a database as a container for site data storage. When you execute a SQL query, the typical process is: connect to the database -> prepare the SQL query - > send the query to the database - > get the results returned by the database - > close the database connection. However, some data in the database is completely static or changes infrequently. The caching system will cache the results of SQL queries to a faster storage system to avoid frequent database operations and greatly improve program execution. time, and caching query results also allows you to process them later.
Commonly used PHP caching technology
Data caching of PHP caching technology:
The data caching mentioned here is Refers to the database query cache. Every time a page is accessed, it will first detect whether the corresponding cached data exists. If it does not exist, connect to the database, obtain the data, and serialize the query results and save them to the file
. The same will happen in the future. The query results are obtained directly from the cache file.
Page caching of PHP caching technology:
Every time a page is accessed, it will first detect whether the corresponding cached page file exists. If it does not exist, connect to the database. , get the data, display the page and generate a cache page file at the same time, so that the page file will play a role the next time you visit. (Template engines and some common cache classes on the Internet usually have this function)
Memory cache of PHP caching technology:
I will not introduce it here, it is not the purpose of this article. Discussion, just briefly mention:
Memcached is a high-performance, distributed memory object caching system, used to reduce database load and improve access speed in dynamic applications.
dbcached is a distributed key-value database memory caching system based on Memcached and NMDB.
Although the above caching technology can well solve the problem of frequent database queries, its disadvantage is that the data is not timely. Here I give the methods I commonly use in projects:
Time-triggered caching of PHP caching technology:
Check whether the file exists and the timestamp is less than the set expiration time. If the timestamp of the file modification is greater than the current timestamp minus the expiration timestamp, Then use the cache, otherwise update the cache.
Do not judge whether the data needs to be updated within the set time, and update the cache after the set time. The above is only suitable for use when timeliness requirements are not high, otherwise please see below.
Content-triggered caching of PHP caching technology:
When data is inserted or updated, the cache is forced to be updated.
Here we can see that when a large amount of data needs to be updated frequently, disk read and write operations will eventually be involved. How to solve it? In my daily projects, I usually do not cache all the content, but cache some content that does not change frequently to solve the problem. But in the case of heavy load, it is best to use shared memory as a cache system.
At this point, PHP caching may be a solution, but its disadvantage is that because each request still needs to be parsed by PHP, the efficiency problem is still more serious under heavy load. In this case, Static caching may be used.
Static Cache of PHP Caching Technology
The static cache mentioned here refers to HTML cache. HTML cache generally does not need to determine whether the data needs to be updated, because it is usually The situations where HTML is used are generally pages whose content does not change frequently. When the data is updated, just force the HTML to be updated.
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