Shantanu's Blog

Corporate Consultant

April 25, 2011

 

Saving images in a table

The binary data should not be saved in a table. It should be saved as a file on the application server and only the name and path should be saved in the table. If you must save the image in a table, you can do so in a normalized way. Here is an example...

This is how a typical table that saves the binary data like user images look like.

CREATE TABLE `user_info` (
`id` int(11) not null auto_increment,
`name` varchar(100),
`address1` varchar(256),
`city` varchar(256),
`country` varchar(256),
`acc_no` varchar(256),
`home_phone` varchar(256),
`office_phone` varchar(256),
`mobile_no` varchar(256),
`date_of_birth` varchar(256),
`age` varchar(256),
`user_photo` blob,
primary key (id)
) ENGINE=InnoDB;

In order to normalize the data, we need to save the images in a separate table. and link the image using the primary key ID of user_info table.

CREATE TABLE `user_pic` (
`id` int(11) NOT NULL auto_increment,
`myfile` longblob,
`dbname` varchar(100),
`tblname` varchar(100),
user_id int,
PRIMARY KEY (`id`),
FOREIGN KEY (`user_id`) references user_info (id)
) ENGINE=InnoDB;
_____

The following shell script will move the user photos from user_info table to user_pic table and link it back to the parent table.

#!/bin/sh
mynum=`date '+%m%d%H%M%S'`
num=1

while (( num < 100 ))
do
mysql test -uroot -pPasswd -e"select user_photo into dumpfile '/tmp/myfile_mar_$mynum_$num.png' from user_info where id = $num"

if [[ -s /tmp/myfile_mar_$mynum_$num.png ]];then
mysql test -uroot -pPasswd -e"insert into user_pic values (NULL, load_file('/tmp/myfile_mar_$mynum_$num.png'), database(), 'user_info', $num)"
fi

let num+=1

done

_____

Once the script is successfully run, drop the column "user_photo" from the user_info table.
ALTER TABLE user_info DROP COLUMN user_photo;

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April 18, 2011

 

Escaping in MySQL

Usually Mysql returns the text as is and does not escape the special characters.

# mysql -ushantanu -pshantanu@123 -Bse"select name from test.todel"
shantanu's
amar"s

If I need the following output, I will have to write a small shell script.

shantanu\'s
amar\"s

You can use mysql_real_escape_string if you are comfortable with PHP, but if you insist on shell, here is a solution assuming name is the second column in the table.
_____

#!/bin/sh
mysqldump -ushantanu -pshantanu@123 test todel --compact --skip-extended-insert --no-create-info > tofile.txt

for customer in `sed -rn 's/.*\(//;s/\).*//p' tofile.txt | awk -F"," '{print $2}' | sed "s/^'//" | sed "s/'$//"`
do
echo $customer
done

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April 06, 2011

 

MySQL and RAMdisk to make queries faster

Here is how you get MySQL to use a 1G size tmpfs.
http://dev.mysql.com/doc/refman/5.1/en/server-options.html#option_mysqld_tmpdir

0. mkdir -p /db/tmpfs01 && chown mysql:mysql /db/tmpfs01
1. mount tmpfs /db/tmpfs01 -t tmpfs -o size=1G
3. edit my.cnf file and add: tmpdir = /db/tmpfs01
4. restart MySQL

To have persistent tmpfs with reboot put the following into /etc/fstab. On this system the mysql user is uid/gid of 27, yours might vary so adjust accordingly.
tmpfs /db/tmpfs01 tmpfs rw,uid=27,gid=27,size=1G,nr_inodes=10k,mode=0755 0 0

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April 05, 2011

 

Controlling mysql access using firewall

If I want to allow a new application server to access mysql on current 3306 port, I need the following command

iptables -I INPUT 13 -s 111.222.333.444 -p tcp --dport 3306 -j ACCEPT

I can check if the rule is set as expected.

iptables -nvL

4 240 ACCEPT tcp -- * * 111.222.333.444 0.0.0.0/0 tcp dpt:3306

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