Enable the query cache in MySQL to improve performance

by on March 24, 2006 · 24 comments· LAST UPDATED July 31, 2007

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If you want to get optimized and speedy response from your MySQL server then you need to add following two configurations directive to your MySQL server:

The amount of memory (SIZE) allocated for caching query results. The default value is 0, which disables the query cache.

Set the query cache type. Possible options are as follows:
0 : Don't cache results in or retrieve results from the query cache.
1 : Cache all query results except for those that begin with SELECT S_NO_CACHE.
2 : Cache results only for queries that begin with SELECT SQL_CACHE

Howto enable caching in MySQL

You can setup caching as follows:
$ mysql -u root –p

Enter password:
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 16 to server version: 4.1.15-Debian_1-log
Type 'help;' or '\h' for help. Type '\c' to clear the buffer.

Now setup cache size 16Mb:

mysql> SET GLOBAL query_cache_size = 16777216;

Query OK, 0 rows affected (0.00 sec)

mysql> SHOW VARIABLES LIKE 'query_cache_size'; 


| Variable_name    | Value    |
| query_cache_size | 16777216 |

You can setup them in /etc/my.cnf (Red Hat) or /etc/mysql/my.cnf (Debian) file:
# vi /etc/my.cnf
Append config directives as follows:

query_cache_size = 268435456

In above example the maximum size of individual query results that can be cached set to 1048576 using query_cache_limit system variable. Memory size in Kb.

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{ 24 comments… read them below or add one }

1 vijay prakash February 7, 2007 at 6:53 am

I wanted to run a website on port 80 through apache webserver but it is showing that port is already in use. When i try to find out which application is running on port 80 by this command

netstat -tulpn | grep :80

it is showing following result

tcp 0 0* LISTEN –

Please help me how can i kill this so that port 80 can be utilised for apache web server.



2 nixCraft February 7, 2007 at 12:47 pm

Stop Apache webserver using
/etc/init.d/httpd stop
killall -9 httpd
Also you need to run netstat -tulpn | grep :80 as root user so you will get program name or PID


3 vijay prakash February 7, 2007 at 1:13 pm


I have already used above commands but still the problem persist. When i use netstat then no pid/program name displays as i have already mentioned the output i am getting in earlier query. Please help me in this situation what should i do.




4 nixCraft February 7, 2007 at 3:18 pm

Restart Linux system. Also note that you must run netstat command as root user. BTW what Linux distro you are using?


5 Shelon Padmore January 17, 2008 at 2:06 pm

Yes a reboot may help. Also try configuring httpd to listen on another port, just to see if all is well with the httpd installation.

Shelon Padmore


6 Siddique January 21, 2008 at 5:21 am

Hi, Nice good information


7 Me April 5, 2008 at 1:04 pm

In one sentence you show a 16MB cache size as 16777216. In another, you explain that the variable values (ie, 16777216) are in KB. You should correct this, as it might confuse folks who don’t know which it is (that is, if you express it as 16777216 it is NOT in KB, it’s in bytes).


8 dog July 11, 2008 at 1:49 am

You might be using skype. Skype is configured to use port 80 and 443 when it can’t use another port for incoming connections. Check your advanced options to turn this off, and Apache will run properly.


9 mmorpg September 27, 2008 at 2:33 am

Thanks, that is always a big concern with multiple databases. Good tips for the MySQL


10 Nathan October 15, 2008 at 8:45 pm

I did some benchmarking with and without this setting enabled and noticed virtually no difference, I performed the exact same SELECT query about 900.000 times and marked the microseconds it took.. so in theory the cache should jump in right away..


11 rapidshare library January 22, 2009 at 11:26 am


size are in bytes not in KB
mysql> SET GLOBAL query_cache_size = 16777216;

16777216 Bytes


12 Mr.Urs February 19, 2009 at 5:37 am

Good information


13 111110100 December 17, 2009 at 8:42 am

You can also explicitly set to my.cnf



14 Purab Kharat October 18, 2010 at 7:22 am

I am having one doubt..When this mysql query cache will be destroyed. Is there any setting available for destroying the cache time.


15 Rob Chant August 18, 2011 at 3:08 pm

It uses a least recently used system for pruning the cache, so there’s no explicit timeout for cached queries.


16 Deepak Agrawal January 3, 2011 at 12:27 am

hey thx a lot very much for this information you have my a lot of time and money thx if you have any other information important in my sql plz inform me


17 Milos Popovic March 1, 2011 at 12:25 pm

Tnx very much, it’s works :D


18 khupcom September 5, 2011 at 1:05 am

query_cache_size = 64M
query_cache_limit= 64M

Not working with mysql 5.5


19 V January 27, 2012 at 9:43 am

How one can determine the need to increase or decrease the query_cache_limit size?


20 MetaKafe May 15, 2012 at 9:02 pm

Thank you verry much..


21 ali August 8, 2013 at 12:49 pm

what is limit of the query cache good for?
how to know best value?

thanks for the information


22 Sohail Ahmed August 12, 2014 at 7:37 am

@Ali, checkout mysqltuner.com.


23 Andrew January 21, 2015 at 10:34 am

The one thing I’m curious about is why would someone NOT use cache? Why is no cache the default setting? Is there a downside to caching?


24 Dave January 30, 2015 at 11:19 am

if you set the cache size to 16Mb by command line in mysql then to set it in the /etc/my.cnf the config should be:

query_cache_size = 16777216

setting query_cache_size = 268435456 in my.cnf sets the cache to 256M


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