echo 1 > /proc/sys/vm/drop_caches a good idea? Post: 302462902

Sponsored Content

Top Forums UNIX for Advanced & Expert Users echo 1 > /proc/sys/vm/drop_caches a good idea? Post 302462902 by Neo on Friday 15th of October 2010 09:24:06 AM

10-15-2010

Administrator

Hi Eric,

Actually, it really does not matter much, frankly speaking. I've experimented with dropping caches in Linux so many times on our production web server (LAMP).

Linux does such a great job at using all available memory, and reclaiming it when needed, so it is better to let Linux manage those things.

When you drop the cache (or caches), you will see the CPU load go up (sometimes way up) because the cache is gone. Available RAM goes up, but it does not matter because performance is slower because the cache is empty.

Then over time, if you leave the caches off, the performance will suffer because you are not taking advantage of the cache.

Linux tries to use all available RAM, so the caches will fill over time if you don't instruct Linux to drop the caches, and this is a good thing. You will see available RAM go down, but don't worry, it is available for applications when needed because applications take higher priority than cache.

You want Linux to use all the RAM. That is a good thing because the kernel is basically using all available RAM that is not used by applications (and the OS) for cache. Dropping caches has little positive effect on performance. In fact, it tends to have a negative effect. The reason is that you are not really making more RAM available to the apps, because the apps already have been given the RAM needed. You simply are dropping the cache, which degrades performance.

Regarding, swappiness, the same is basically true. Linux will dump the cache before swapping, as I recall, but I would need to read up on that again to see exactly how it works.

We have experimented with swappiness, and ours is currently set to:

Code:

# cat swappiness
20

... and FYI:

Code:

# cat drop_caches
0

This User Gave Thanks to Neo For This Post:

Neo

View Public Profile for Neo

Visit Neo's homepage!

Find all posts by Neo

8 More Discussions You Might Find Interesting

1. UNIX for Dummies Questions & Answers

Dual Boot a good idea?

I was just wondering if it would be alright to dual boot a machine with both UNIX using XTERM for the interface and windows 98 or if people consider this a bad idea? if you consider it bad do tell me some possible alternatives..also would it be better to get linux over pure unix? I'd like a visual...

2. Shell Programming and Scripting

Limitations of awk? Good idea? Bad idea?

Keeping in mind that I'm relatively comfortable with programming in general but very new to unix and korn/bourne shell scripts.. I'm using awk on a CSV file, and then performing calculations and operations on specific fields within specific records. The CSV file I'm working with has about 600...

3. Shell Programming and Scripting

Echo escaped \c in SH Shell Any Idea

Hi All, I have got an echo statement with "\c" in it to avoid getting into a newline. Ths script is using #!\bin\sh Any idea what could make it to escape "\c"

4. Shell Programming and Scripting

any good idea on this?

txt file like this, 1 2 3 4456 a bb c d 3 f e 1 k 32 d m f e 123 m 2 k every line contains 3 or more columns, all the columns are separated by space, and every column includes 1 to 3 character. what I wanna do is deleting the first three columns, and keep the rest no matter how long...

5. Linux

Kernal panic error& setuproot:error mounting /proc&/sys

Hi all, I am new to redhat/fedora linux. In fedora linux 6,we created one file system(hda3 - /fs). in this mount poing we were installed mounta vista os. while booting we are getting below error messages. 1) Booting 'mountaVisat(2.6.18_pro 500_pc_target-x86_586 smp)' root(hd0,1)...

6. Shell Programming and Scripting

Compact script with array - Good idea?

Hi, I have a shell script where a lot of the code is repeated. I wanted to make the code much more compact so I spoke to a guy and he suggested using arrays, like follows: #!/bin/bash readonly -a nginx=('nginx' '--prefix=/opt' '-j 4' 'http://nginx.org/download/nginx-1.2.2.tar.gz' )...

7. Solaris

Drop_caches doesn't work on Solaris but works on RHEL6

Hello Experts, I am performing performance tests on a few mysql select queries. I use the following command to clear the memory disk caches. sync && echo 3 | sudo tee /proc/sys/vm/drop_caches I however see that the above command works on RHEL6 but doesn't work on Solaris 10. I asked...

8. IP Networking

Cat /proc/sys/net/ipv4/ip_local_port_range

Hello, /proc/sys/net/ipv4/ip_local_port_range returns 32000 - 61000, i have a client TCP and a Server TCP. i have used bind() only on the server, the port of socket client is given by the OS that's it ? it retrieves this port from this range (/proc/sys/net/ipv4/ip_local_port_range) ? ...

LEARN ABOUT MOJAVE

klist

KLIST(1)						    BSD General Commands Manual 						  KLIST(1)

NAME

     klist -- list Kerberos credentials

SYNOPSIS

     klist [-c cache | --cache=cache] [-s | -t | --test] [-T | --tokens] [-5 | --v5] [-v | --verbose] [-l | --list-caches] [-f] [--version]
	   [--help]

DESCRIPTION

     klist reads and displays the current tickets in the credential cache (also known as the ticket file).

     Options supported:

     -c cache, --cache=cache
	     credential cache to list

     -s, -t, --test
	     Test for there being an active and valid TGT for the local realm of the user in the credential cache.

     -T, --tokens
	     display AFS tokens

     -5, --v5
	     display v5 cred cache (this is the default)

     -f      Include ticket flags in short form, each character stands for a specific flag, as follows:
		   F	forwardable
		   f	forwarded
		   P	proxiable
		   p	proxied
		   D	postdate-able
		   d	postdated
		   R	renewable
		   I	initial
		   i	invalid
		   A	pre-authenticated
		   H	hardware authenticated

	     This information is also output with the --verbose option, but in a more verbose way.

     -v, --verbose
	     Verbose output. Include all possible information:

		   Server
			 the principal the ticket is for

		   Ticket etype
			 the encryption type used in the ticket, followed by the key version of the ticket, if it is available

		   Session key
			 the encryption type of the session key, if it's different from the encryption type of the ticket

		   Auth time
			 the time the authentication exchange took place

		   Start time
			 the time that this ticket is valid from (only printed if it's different from the auth time)

		   End time
			 when the ticket expires, if it has already expired this is also noted

		   Renew till
			 the maximum possible end time of any ticket derived from this one

		   Ticket flags
			 the flags set on the ticket

		   Addresses
			 the set of addresses from which this ticket is valid

     -l, --list-caches
	     List the credential caches for the current users, not all cache types supports listing multiple caches.

SEE ALSO

     kdestroy(1), kinit(1)

HEIMDAL 
							  October 6, 2005							   HEIMDAL