Showing entries 1 to 4
Displaying posts with tag: swappiness (reset)
vm.swappiness and OOM in RHEL6

The behavior of vm.swappiness was always a bit confusing for novice linux users, as setting vm.swappiness to 0 would not completely disable swapping in the system during a memory crunch. vm.swappiness would only affect the agressiveness of swapping.

Following upstream commit tried to give more control to parameter. This commit tried to avoid swapping completely when vm.swappiness is set to 0.

commit fe35004fbf9eaf67482b074a2e032abb9c89b1dd
Author: Satoru Moriya
Date: Tue May 29 15:06:47 2012 -0700
mm: avoid swapping out with swappiness==0

With above commit, setting vm.swappiness to “0” instructs the kernel not to initiate swapping until the amount of free and file-backed pages is less than the high water mark in a memory zone. In other words, it tries to reclaim as much memory that can be reclaimed, before swapping starts.
This greatly reduced the chances of swapping.

When this …

[Read more]
MySQL Swap Insanity: Solved

Yes, it has been a while since my last post.  Still in the midst of MySQL ecosystem, and enjoying it tremendously.  I thought I would make this post as it relates to a topic that has some varied results in the online world, and I would like to kick start this blog again.  We'll see how that goes... :)

MySQL has been able to harness the potential of more powerful (CPU) and larger (RAM, disk space

OOM relation to vm.swappiness=0 in new kernel

I have recently been involved in diagnosing the reasons behind OOM invocation that would kill the MySQL server process. Of course these servers were primarily running MySQL. As such the MySQL server process was the one with the largest amount of memory allocated.

But the strange thing was that in all the cases, there was no swapping activity seen and there were enough pages in the page cache. Ironically all of these servers were CentOS 6.4 running kernel version 2.6.32-358. Another commonality was the fact that vm.swappiness was set to 0. This is a pretty much standard practice and one that is applied on nearly every server that runs MySQL.

Looking into this further I realized that there was a change introduced in kernel 3.5-rc1 that altered the swapping behavior when “vm.swappiness=0″.

Below is the description of the commit that changed “vm.swappiness=0″ behavior, together with the diff:

$ git …
[Read more]
An incomplete guide to linux system configuration for MySQL

As a former Oracle DBA, I know how the system and the database are linked.
The first one who told me that the installation of Oracle has never been a problem is a liar!
Yes, your database and your system are the best of friends, you must respect that.

I’d make a list of linux system settings to configure a MySQL databases server and share my sources with you.
In return, I would like you to share your sources with the community by publishing your tips in the comments.



  • This parameter allows to specify how the kernel must manage the memory swap
  • Default value : 60 (Range 0 to 100)
  • Value to set : 0 (it will swap only to avoid an out of memory condition)
  • How to set a new non-persistent value :  sysctl -w vm.swappiness=0
  • How to store a new persistent value : add …
[Read more]
Showing entries 1 to 4