Common problems and solutions for using Memcache cache in PHP

In web applications, caching is a very important technology. Caching can greatly reduce the load on the database and server and improve the performance of web applications. Memcache is a high-performance distributed memory cache system commonly used in web applications. When using Memcache cache in PHP, some problems sometimes occur. This article will introduce these problems and their solutions.

Problem 1: Unable to connect to the Memcache server
When using Memcache cache, the first problem encountered may be the inability to connect to the Memcache server. The main reason for this situation is that the Memcache server is not running or the port is not open. The following are some possible solutions:

1. Check whether the Memcache server is started. You can check whether the Memcache server is running by entering the command "service memcached status" in the terminal.

2. Check whether the Memcache server opens the port. You can check whether the Memcache server is listening on port 11211 by entering the command "netstat -ant | grep 11211" in the terminal (assuming Memcache's default port is 11211). If not, you can configure Memcache in the server and open port 11211.

3. Check the firewall settings. It is possible that the server firewall prohibits access to the Memcache server. In CentOS, the firewall can be turned off by entering the command "systemctl stop firewalld.service".

Question 2: Cache invalidation
When using Memcache cache in PHP, sometimes you will encounter cache invalidation. That is, the data is read from the cache, but no matter how many times it is read, the data will not be updated. Here are some possible solutions:

1. Check the cache key name. When using Memcache cache, ensure that the key name is unique and not repeated. If key names are duplicated, one key-value pair may overwrite another key-value pair.

2. Check the cache expiration time. When setting up the cache, make sure the expiration time is normal. For example, the expiration time should be set to a timestamp plus minutes, not seconds.

3. Check whether the Memcache server is working properly. If the Memcache server fails, the cached data cannot be updated. You can check the status of the Memcache server by entering the command "memcached-tool [server address]:11211 stats" in the terminal.

Problem 3: The cache is destroyed
When using Memcache cache in PHP, sometimes the cache is destroyed. That is, data is read from the cache, but the data is incomplete or the data content is inconsistent with what was previously stored. Here are some possible solutions:

1. Check the cache key name. Make sure the key name is unique and not repeated. If key names are duplicated, one key-value pair may overwrite another key-value pair.

2. Check the serialization method of cached data. When storing data into Memcache, ensure that the correct serialization method should be used. For example, when storing an array, you should use the serialize function to serialize the array and then store it in Memcache. When reading data, you should use the unserialize function to deserialize the data. If you use the wrong serialization method, it will cause data storage and reading errors.

3. Check the Memcache server version. When using Memcache cache, ensure that the Memcache server version is the same as the version used by the client. For example, if the client is using PHP 5.x, Memcache version 2.x should be used. If the versions do not match, data corruption may occur.

Conclusion:
When using Memcache cache in PHP, we need to carefully review the above common problems and solve the problems in a timely manner so that the cache function can function normally and maximize the performance of web applications.

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