How to solve the Apache high memory usage problem?

1. Optimize Apache Configuration: Apache HTTP server has many configuration options which can be tailored to specific system requirements. Modules that are not needed can be disabled in apache’s configuration file.

1. Limit the number of child processes: In your Apache configuration file, you can limit the number of child processes that Apache can spawn. Use the directives like ‘MaxRequestWorkers’ (earlier ‘MaxClients’) and ‘MaxConnectionsPerChild’ (earlier ‘MaxRequestsPerChild’).

1. Use a different MPM (Multi-Processing Module): Apache comes with several different MPMs. The commonly used ones are Prefork and Worker. Since the Worker MPM uses threads to scale the number of clients that can be served, it is not unusual for it to use less memory than the Prefork MPM.

1. Use mod\_reqtimeout to avoid slow read/write: This module provides a way to set timeouts for input and output, helping to prevent slow read/write attacks which can consume server resources.

1. Regularly Monitor Apache: Use Apache’s mod\_status or command line utilities like ‘ab’, ‘apachetop’, ‘htop’ etc. to monitor Apache’s performance over time.

1. Optimize your website code or script: Sometimes poorly written script can consume more memory, optimizing your PHP or any other web script can also helps to reduce the memory usage.

1. Use a CDN: Content Delivery Networks can serve static files from servers nearer to the client, which reduces the load on your own server.

1. Updating Apache: Sometimes the issue may be due to a bug or problem with the specific version of Apache you are using. Hence, it’s good to have the updated version installed.

1. Tuning the OS: Turn off services which are not needed. Every OS service consumes a certain amount of resources and disabling those not needed helps to free resources for Apache.

1. If nothing else works, upgrade your hardware. Sometimes, you just need more RAM. Especially if your site is very busy, it might be more cost-effective to upgrade your server rather than spending time to perfect your Apache configuration.