CPU Utilization

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  1. CPU Utilization: A Server Engineer's Guide

This article provides a comprehensive overview of CPU utilization for MediaWiki server administrators. Understanding CPU usage is crucial for maintaining optimal performance and identifying potential bottlenecks. This guide is geared towards newcomers to server administration within the context of a MediaWiki deployment.

What is CPU Utilization?

CPU utilization refers to the percentage of time that a central processing unit (CPU) is actively processing instructions. A CPU constantly switches between tasks, and utilization measures how much time it spends *doing* work versus being idle. High CPU utilization isn't inherently bad, but sustained high levels (especially approaching 100%) can indicate performance issues. Low CPU utilization isn’t *always* good either; it could signify under-provisioning, but also potentially indicate that resources are waiting on I/O or other processes. Monitoring CPU utilization helps in capacity planning, troubleshooting, and ensuring a responsive wiki experience for users.

Factors Affecting CPU Utilization in MediaWiki

Several factors can contribute to high CPU usage on a MediaWiki server. These include:

  • Number of Concurrent Users: More active users mean more requests to process, leading to higher CPU load.
  • Page Complexity: Pages with many images, templates, or complex parser functions require more processing power. See Help:Templates for more information on template usage.
  • Database Queries: Inefficient or numerous database queries are a common source of CPU bottlenecks. Efficient database design is covered in Manual:Database
  • Search Indexing: The Manual:Search index requires periodic updates, which can consume significant CPU resources.
  • External Scripts & Extensions: Third-party extensions and custom scripts can add to the overall CPU load. Review Manual:Extensions for details.
  • Caching: Insufficient caching forces the server to repeatedly perform the same calculations, increasing CPU usage. See Manual:Caching for configuration options.
  • Cron Jobs: Scheduled tasks (cron jobs) can spike CPU usage during their execution. See Manual:Configuration for cron job settings.


Monitoring CPU Utilization

There are several tools available for monitoring CPU utilization on a Linux server.

  • top: A command-line utility that displays real-time system information, including CPU usage per process.
  • htop: An enhanced version of `top` with a more user-friendly interface.
  • vmstat: Reports virtual memory statistics, including CPU usage.
  • sar: Collects, reports, and saves system activity information.
  • Grafana/Prometheus: Powerful monitoring and alerting systems, often used in larger deployments.

CPU Usage Breakdown

Understanding what the CPU is doing is as important as knowing the overall utilization. Linux categorizes CPU time into different states:

State Description
User Time spent running user processes. System Time spent running kernel processes (system calls). Idle Time the CPU is not processing any tasks. Iowait Time the CPU is waiting for I/O operations to complete. Steal Time a virtual CPU spends waiting for a real CPU while the hypervisor is servicing another virtual processor. Nice Time spent running low-priority processes.

High `iowait` suggests a disk I/O bottleneck. High `steal` indicates contention on the hypervisor (in a virtualized environment).

Interpreting CPU Utilization Levels

The "acceptable" level of CPU utilization depends on your server's capacity and the performance expectations of your users. Here's a general guideline:

Utilization Interpretation Action
< 20% Low utilization. Server has ample capacity. Monitor for trends. Consider reducing server resources if consistently low.
20% - 80% Moderate utilization. Server is operating normally. Continue monitoring. Optimize database queries and caching if performance degrades.
80% - 95% High utilization. Server is nearing capacity. Investigate the cause. Optimize code, increase caching, or consider scaling up the server.
> 95% Critical utilization. Server is overloaded. Immediate action required. Identify and resolve the bottleneck. Consider scaling up or adding more servers.

Troubleshooting High CPU Utilization

If you identify consistently high CPU utilization, follow these steps:

1. Identify the Culprit: Use `top` or `htop` to determine which processes are consuming the most CPU. Often, it will be the web server (e.g., Apache or Nginx) and the PHP process (php-fpm or mod_php) running MediaWiki. 2. Analyze Slow Queries: Use your database's slow query log to identify inefficient SQL queries. See Manual:Database for details on query optimization. 3. Optimize Caching: Configure appropriate caching mechanisms (e.g., Memcached, Redis) to reduce the load on the database. Refer to Manual:Caching for configuration. 4. Review Extensions: Disable or update any extensions that are suspected of causing high CPU usage. Consult the Extension Directory for updated versions. 5. Code Profiling: If you've written custom code, use a PHP profiler (like Xdebug) to identify performance bottlenecks. 6. Hardware Upgrade: If software optimization doesn't resolve the issue, consider upgrading the server's CPU or adding more CPUs.

Server Specifications Example

Here's an example of server specifications that can handle a medium-sized MediaWiki installation:

Component Specification
CPU Intel Xeon E5-2680 v4 (14 cores)
RAM 32 GB DDR4
Storage 1 TB SSD
Network 1 Gbps
Operating System Ubuntu Server 20.04 LTS

These specifications are examples and will vary based on the size and traffic of your wiki.


Related Topics


Intel-Based Server Configurations

Configuration Specifications Benchmark
Core i7-6700K/7700 Server 64 GB DDR4, NVMe SSD 2 x 512 GB CPU Benchmark: 8046
Core i7-8700 Server 64 GB DDR4, NVMe SSD 2x1 TB CPU Benchmark: 13124
Core i9-9900K Server 128 GB DDR4, NVMe SSD 2 x 1 TB CPU Benchmark: 49969
Core i9-13900 Server (64GB) 64 GB RAM, 2x2 TB NVMe SSD
Core i9-13900 Server (128GB) 128 GB RAM, 2x2 TB NVMe SSD
Core i5-13500 Server (64GB) 64 GB RAM, 2x500 GB NVMe SSD
Core i5-13500 Server (128GB) 128 GB RAM, 2x500 GB NVMe SSD
Core i5-13500 Workstation 64 GB DDR5 RAM, 2 NVMe SSD, NVIDIA RTX 4000

AMD-Based Server Configurations

Configuration Specifications Benchmark
Ryzen 5 3600 Server 64 GB RAM, 2x480 GB NVMe CPU Benchmark: 17849
Ryzen 7 7700 Server 64 GB DDR5 RAM, 2x1 TB NVMe CPU Benchmark: 35224
Ryzen 9 5950X Server 128 GB RAM, 2x4 TB NVMe CPU Benchmark: 46045
Ryzen 9 7950X Server 128 GB DDR5 ECC, 2x2 TB NVMe CPU Benchmark: 63561
EPYC 7502P Server (128GB/1TB) 128 GB RAM, 1 TB NVMe CPU Benchmark: 48021
EPYC 7502P Server (128GB/2TB) 128 GB RAM, 2 TB NVMe CPU Benchmark: 48021
EPYC 7502P Server (128GB/4TB) 128 GB RAM, 2x2 TB NVMe CPU Benchmark: 48021
EPYC 7502P Server (256GB/1TB) 256 GB RAM, 1 TB NVMe CPU Benchmark: 48021
EPYC 7502P Server (256GB/4TB) 256 GB RAM, 2x2 TB NVMe CPU Benchmark: 48021
EPYC 9454P Server 256 GB RAM, 2x2 TB NVMe

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⚠️ *Note: All benchmark scores are approximate and may vary based on configuration. Server availability subject to stock.* ⚠️

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