There is a hidden danger in CDH: the exchange memory used by the process of this role is XX megabytes. Warning threshold: 200 bytes

summary

CDH Warning message of a service on ：
Existence hidden danger : The swap memory used by the process of this role is xx Megabytes . Warning threshold :200 byte

for example ：
ZooKeeper The service process uses Swap memory , Lead to ZooKeeper Service slows down , It affects the cluster

Personal understanding of swap memory

• English name ：swap space
• Translated names ： Swap space or Swap memory
• paraphrase ：
  swap space It's a piece of space on the hard disk
  When the physical memory of the system is insufficient , The memory of some programs that have not been operated for a long time will be released , The free space is temporarily saved to swap space
  When the program is ready to operate , Again from swap space Restore data to memory
• advantage ： Enables the program to manipulate space larger than the actual physical memory
• shortcoming ：swap space Will produce hard disk IO, Make the program slow

for example
Windows The system can run multiple programs at the same time , When switching to a program that has been ignored for a long time , You'll hear the hard drive “ Dada ” Direct sound

Swap memory related operations

View swap memory

free -h

swap space Total size 8G, Already used 2.2G, The remaining 5.8G

Enable swap memory

swapon -a

• Options -a, --all
• original text ：
  All devices marked as swap in /etc/fstab are made available, except for those with the noauto option.
  Devices that are already being used as swap are silently skipped.
• translation ：
  All in /etc/fstab The marked swap All devices are available , Except with noauto Optional device .
  Devices that have been used as switching areas are silently skipped .

Disable swap memory

swapoff -a

A window executes swapoff -a, Another window executes swapon

You can see , The used swap space is decreasing

CDH Hidden danger solution

Write a script , Set timing task , Regularly clean the used swap space

#!/bin/bash
#  Disable all swap spaces 
swapoff -a
#  Enable all swap spaces 
swapon -a
#  Prompt after cleaning 
echo " Clean up "

Clean up the used swap space after