Ajcody-Mysql-Topics

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Mysql

Actual Mysql Topics Homepage

Please see Ajcody-Mysql-Topics

Mysql Issues And Memory Usuage

My Ajcody-General-Notes#Trouble_Shooting_Memory_Issues has some stuff on memory troubleshooting - generalities.

Our performance guide for Mysql:

http://wiki.zimbra.com/index.php?title=Performance_Tuning_Guidelines_for_Large_Deployments#MySQL

Variable Within MySQL & Zimbra

These percentages below are used against physical RAM - disregard swap in the percentage division.

From the above url, we get some details.

"By default, we try to reserve 30% of system memory for use by this process, and 40% for use by MySQL."
# ZCS 5.0 and later
$ zmlocalconfig -e mailboxd_java_heap_memory_percent=40
Java - mailboxd_java_heap_memory_percent=

The command to set the java percentage is:

 zmlocalconfig -e mailboxd_java_heap_memory_percent=30
Mysql - mysql_memory_percent & my.cnf w/ innodb_buffer_pool_size

Looks like there's an issue with the command/variable (zmlocalconfig -e mysql_memory_percent=##) in regards to MySQL though.

"There is a local config variable [mysql_memory_percent] for mysql memory percent, but today my.cnf doesn't get rewritten after install, so you have to edit my.cnf for this setting if you want to change it."

In summary, this variable [ mysql_memory_percent ] for MySQL is basically not working.

Do this to get memory in bytes for division numbers:

free -b

Figure out what your % in bytes using the physical memory (Mem:) output. Now edit the /opt/zimbra/conf/my.cnf file to change the following line with your memory percentage in bytes:

vi /opt/zimbra/conf/my.cnf
#Modify this var to adjust memory usage
innodb_buffer_pool_size = xxx

This will require a restart.

A GREAT forum post on this is here:

So other background info:

Mysql And Swap

See this article first before exploring the options below.

Should you have your swap file enabled while running MySQL ?

Set swappiness Kernel Var To 0

Source of this summary is here: [http://www.mysqlperformanceblog.com/2007/09/28/heikki-tuuri-to-answer-your-in-depth-innodb-questions/#comment-174442 Swappiness To 0"

Set it on running box:

echo 0 > /proc/sys/vm/swappiness

Set it to persist after reboot - vi /etc/sysctl.conf :

vm.swappiness = 0

The value is a percentage. By setting it to 100, Linux will always swap programs out and never shrink the buffer cache.

Swap Ram Disk Instead Of Disk

Source of this summary is here:

MySQL and the Linux swap problem

Make a (or some) swap disks:

mkdir /mnt/ram0
dd bs=1024 count=14634 if=/dev/zero of=/mnt/ram0/swapfile
mkswap /mnt/ram0/swapfile
swapon /mnt/ram0/swapfile

Will look like this:

[root@mail3 ~]# mkdir /mnt/ram0

[root@mail3 ~]# dd bs=1024 count=14634 if=/dev/zero of=/mnt/ram0/swapfile
14634+0 records in
14634+0 records out
14985216 bytes (15 MB) copied, 0.246329 seconds, 60.8 MB/s

[root@mail3 ~]# mkswap /mnt/ram0/swapfile 
Setting up swapspace version 1, size = 14979 kB

[root@mail3 ~]# free
             total       used       free     shared    buffers     cached
Mem:       1555472    1461200      94272          0     159400     344328
-/+ buffers/cache:     957472     598000
Swap:      2031608        104    2031504

[root@mail3 ~]# swapon /mnt/ram0/swapfile 

[root@mail3 ~]# free
             total       used       free     shared    buffers     cached
Mem:       1555472    1476252      79220          0     159404     344376
-/+ buffers/cache:     972472     583000
Swap:      2046232        104    2046128

[root@mail3 ~]# swapon -s
Filename				Type		Size	Used	Priority
/dev/mapper/VolGroup00-LogVol01         partition	2031608	104	-1
/mnt/ram0/swapfile 
                     file		14624	0	-2
[root@mail3 ~]# cat /proc/swaps 
Filename				Type		Size	Used	Priority
/dev/mapper/VolGroup00-LogVol01         partition	2031608	104	-1
/mnt/ram0/swapfile                      file		14624	0	-2


Just add those lines to your relevant startup file, like /etc/rc.d/rc.local, and it’ll persist after reboots. </pre>

O_DIRECT On Linux And INNODB To Fix Swapping

Source reference for this part is here:

Using O_DIRECT on Linux and INNODB to Fix Swap Insanity

See also: Ajcody-Server-Topics#O_DIRECT_And_Ext3_On_Linux_As_Possible_Reason_For_Corruption

IO_DIRECT And Ext3 On Linux As Possible Reason For Corruption

This is being investigated. Below are my notes on the issue.

Mysql Database Corruption/Repair

Please see the Mysql_Crash_Recovery page rather than the normal search results that give mysql-logger details.

Manual Change Of Mysql Passwords

Please see:

http://wiki.zimbra.com/index.php?title=Issues_with_mysql_and_logmysql_passwords
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