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Enable the query cache in MySQL to improve performance

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:

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

query_cache_type=OPTION
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
Output:

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.
mysql>

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'; 

Output:

 +------------------+----------+
| 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
query_cache_type=1
query_cache_limit=1048576

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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Comments on this entry are closed.

  • vijay prakash February 7, 2007, 6:53 am

    Sir,
    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 0.0.0.0:80 0.0.0.0:* LISTEN –

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

    Vijay

  • nixCraft February 7, 2007, 12:47 pm

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

  • vijay prakash February 7, 2007, 1:13 pm

    Sir,

    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.

    thankyou.

    vijay

  • nixCraft February 7, 2007, 3:18 pm

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

  • Shelon Padmore January 17, 2008, 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

  • Siddique January 21, 2008, 5:21 am

    Hi, Nice good information

  • Me April 5, 2008, 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).

  • dog July 11, 2008, 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.

  • mmorpg September 27, 2008, 2:33 am

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

  • Nathan October 15, 2008, 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..

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

    here

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

    16777216 Bytes

  • Mr.Urs February 19, 2009, 5:37 am

    Good information

  • 111110100 December 17, 2009, 8:42 am

    You can also explicitly set to my.cnf

    query_cache_size=256M
    query_cache_type=1
    query_cache_limit=1M

  • Purab Kharat October 18, 2010, 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.

    • Rob Chant August 18, 2011, 3:08 pm

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

  • Deepak Agrawal January 3, 2011, 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

  • Milos Popovic March 1, 2011, 12:25 pm

    Tnx very much, it’s works :D

  • khupcom September 5, 2011, 1:05 am

    [mysqld_safe]
    query_cache_type=1
    query_cache_size = 64M
    query_cache_limit= 64M

    Not working with mysql 5.5

  • V January 27, 2012, 9:43 am

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

  • MetaKafe May 15, 2012, 9:02 pm

    Thank you verry much..

  • ali August 8, 2013, 12:49 pm

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

    thanks for the information

  • Sohail Ahmed August 12, 2014, 7:37 am

    @Ali, checkout mysqltuner.com.

  • Andrew January 21, 2015, 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?

  • Dave January 30, 2015, 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
    query_cache_type=1
    query_cache_limit=1048576

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