PHP interview

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• CORS (cross origin resource sharing) cross-domain resource sharing , which allows cross-site resource requests. The client needs to use a specific method to request resources (such as xmlhttprequest) and needs to bring specific header information. The server must also support cross-domain resource requests

memcache and redis Similarities and differences

• memcache can utilize multi-threading, has high throughput, and is suitable for large visits

• memcache only supports simple key/value structures

• memcache cannot persist data and cannot be backed up. It can only be used for caching. Data will be lost after restarting.

• Because memcache supports multiple Thread operation, so the issue of data consistency must be considered, and cas (check and set) optimistic locking is used

• Since redis is single-formed, it can ensure the orderliness of operations

• Redis supports a variety of data structures, key/value, list, set, zset, dict, etc.

• Redis data can be stored persistently. Store the data in the disk and can read it out when restarting again

• redis supports data backup, that is, data backup in master-slave mode

Web project high concurrency solution

• Static html, statically use commonly used but rarely updated data

• Separate image servers to avoid Affects the application server. At the same time, individual configuration optimization, cache settings, etc. can be performed for the picture server.

• Database cluster, library table hash
  

• Database cluster can realize reading and writing separation and improve the database response speed. It is generally one master and multiple slaves, or x master and y slave. For example, when writing less and reading more, one server is dedicated to writing operations, and other servers are used for reading operations. This can avoid the impact of read-write locks. However, after the write operation is completed, the data needs to be synchronized.

• Another benefit of a database cluster is that when one database server goes down, there is still complete data on other servers

• In a distributed database, there are multiple nodes in the system, and each node performs different functions. If a node dies, the corresponding function cannot be completed.

• The difference between database cluster and distributed database. Suppose a task takes one hour to complete on one node, and there are now 10 such tasks and 10 nodes. The distributed database can split the task into 10 tasks. Each node completes a different task, regardless of the dependencies of the subtasks. All tasks will be completed after an hour. Each node in the database cluster can complete a complete task. It can average 10 tasks to each node, so that all tasks are completed after one hour.

• sql optimization

• If there is too much data in the table, you can consider splitting the table and then using hash mapping

• Index optimization

• Cache

• Mirror, used to improve access speed

• Load balancing, solving high concurrency and massive access problems

• CDN, allowing users to access the nearest cdn server and get the fastest response

• Data compression

PHP

Magic method

• ##__set/__get handles attributes that do not exist in the class

• #__call/_callStatic is triggered when a method/static method that does not exist in the class is called. __callStatic itself must also be declared as a static method

• __toString Convert the object into a string and output it

• __invoke Treat the object as a function to execute

The difference between require and include

Except for the error handling, everything else is the same. require generates a fatal error and the script stops running. include will generate a warning, but the script will continue to run

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