What causes high server load? How to identify the part that is under load

My name is Ito and I am an infrastructure engineer

Last time, we introduced "load average," which can be checked when server load increases.
How to check server load with load average? Beyond Blog

The load average indicates the number of processes waiting to be processed.
The higher the number, the more processes are waiting to be processed, indicating a "heavy load."

This time, I would like to explore the causes of high load situations

There are two main reasons for this:

There are basically two main reasons why a high load average occurs

• CPU processing cannot keep up
• Disk I/O processing cannot keep up

Now, I would like to explain how to find the cause of each of these

If the CPU is the cause

First, check the CPU usage using the top command. The following two values ​​are important:

If a typical process is CPU intensive, you will likely see high CPU usage in user mode (%user)

Additionally, when a user mode process is running a large number of processes, it will switch processes etc.
This "process switching" will use the kernel mode (%system) CPU, so
for programs that switch processes frequently, the kernel mode CPU usage will be high.

High user mode CPU usage

High kernel CPU usage

If the cause is disk I/O

If disk I/O is the problem, check the following in top:

The iowait value is often high when a large amount of data is being read or written from the disk.
For example, a DB server with a lot of database access is likely to have a high iowait value.

SWAP is the capacity that is used on the HDD instead of memory when a process has used up all of the memory.
An example of using SWAP is when a web server, etc., allocates memory and uses SWAP when there is a large amount of access.

When using SWAP, the server will be slower because the HDD is used instead of memory, which increases the load on disk I/O

High iowait and high load due to disk I/O

If you are using SWAP

We will investigate the cause

This should help you determine whether the problem is CPU or I/O.
Use the ps command to find out which process is using the CPU (or memory in the case of SWAP).

If the CPU usage rate in user mode is high, there are no problems with I/O, etc., so you
may need to increase CPU performance or review your program.

If there is a problem with the disk I/O, you may need to add more memory or review the program to perform processing in a location with available memory rather than using disk I/O

Also, if the load average is low but processing is slow,
there may be a problem with the software settings or network processing.

When you are faced with the problem of "high load," the first step to solving it is to stay calm and identify which part is under load

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