Working out what is consuming the machine.
WHAT TO ESTABLISH FIRST
Whether load is processor, memory or disk.
HOW
Look at the wait figure and swap activity in top.
WHAT HIGH PROCESSOR USE POINTS TO
A specific process, visible at the top of the list.
WHAT HIGH WAIT POINTS TO
Disk, or a database reading heavily.
WHAT HIGH MEMORY WITH SWAPPING POINTS TO
Too many processes, or one that has grown.
WHAT TO CHECK ON A WEB SERVER
Which site is generating the requests Whether one account dominates Whether traffic is genuine or automated
HOW TO FIND THE BUSIEST SITE
Count requests per domain in the access logs.
HOW TO FIND THE BUSIEST SOURCE
Count requests per address.
WHAT TO LOOK AT IN THE DATABASE
The process list, for long-running queries The slow query log
WHY DATABASES ARE THE USUAL CAUSE
An unindexed query on a growing table degrades suddenly rather than gradually.
WHAT TO CHECK BEFORE BLAMING TRAFFIC
Whether a backup, update or scan is running.
WHY
Scheduled work explains a great many load spikes.
WHAT TO DO FOR IMMEDIATE RELIEF
Identify and stop the single worst offender.
WHAT TO DO AFTERWARDS
Establish why it was possible.
