Summer: 2013

Thursday, 12 September 2013

Struct and pointer sample

#include <stdio.h>

typedef struct Table Table;

struct Table {
        int Height;
        int Width;
};

Table * create_table(int height, int width)
{
    Table *mytable_ptr;

    Table my = {height, width};

    mytable_ptr = &my;

    return mytable_ptr;

}

int main()
{
        Table * my;
        my = create_table(10, 20);

       int height = my->Height;

       printf("h%d\n", height);
}

Friday, 7 June 2013

Test tomcat 6.0 installation in Ubuntu 12

1. compile a test servlet

a. create a java class named PuppyServlet.java

package dog;
import java.io.*;
import javax.servlet.http.*;
import javax.servlet.*;
public class PuppyServlet extends HttpServlet {
    public void doGet (HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException
    {
res.setContentType("text/html");

            PrintWriter out = res.getWriter();
            out.println("<html><body>");
            out.println("<center>Hello, world! I have a cute puppy</center>");
            out.println("</body></html>");
            out.close();
    }
}

b. set class path in .bashrc

export CLASSPATH=/usr/share/java/servlet-api.jar

c. compile

javac PuppyServlet.java

2. create directories and configure file to deploy this sevlet

a. go to /var/lib/tomcat6/webapps create a directories

cd /var/lib/tomcat6/webapps
mkdir test
cd test
mkdir WEB-INF
cd WEB-INF
mkdir classes
cd classes
mkdir dog

b. put PuppyServlet.class in dog directory

c. create web.xml file and put it in WEB-INF direcory

<web-app version="2.4" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/j2ee" xsi:schemalocation="http:/java.sun.com/dtd/web-app_2_3.dtd">
<servlet>
<servlet-name>test</servlet-name>
<servlet-class>dog.PuppyServlet</servlet-class>
</servlet>

<servlet-mapping>
<servlet-name>test</servlet-name>
<url-pattern>/mytest</url-pattern>
</servlet-mapping>
</web-app>

3. go to http://localhost:8080/test/mytest

should see: Hello, world! I have a cute puppy

Thursday, 6 June 2013

Enviorment variables

1. View all environment variables
export -p

2. View individual variables
echo $variable_name

3. Set variable dynamically
export APPLICATION_ENV='local'

4. Set variable permanently
put export statement in .profile

Wednesday, 27 March 2013

More MySql tips

dump db

mysqldump --host='127.0.0.1' --user=root --password='passwd' --column-statistics=0  db_name>dw.sql

redirect result to a csv file

select * from usermanager_users
 into outfile '/tmp/test.csv' fields terminated by ',' enclosed by '"' 
 lines terminated by '\n';

redirect result on command line

mysql -u [username ] -p[password] [db_name] -e " SELECT * FROM [tbl_name] " > file_name

Case sensitive compare

#Will match first name Mary, but not match mary
SELECT first_name FROM  `name` WHERE first_name  REGEXP BINARY 'Mary';

Show stored procedures

SHOW PROCEDURE STATUS WHERE Db = 'db_name'\G

# show details of procedure
SHOW CREATE PROCEDURE procedure_name\G

Create a mysql user

CREATE USER lshen@'10.18.276.170' IDENTIFIED   BY 'eikdkdk123scx';

select * from mysql.user where User="lshen"\G

GRANT SELECT  ON *.* TO lshen@'10.18.276.170';

FLUSH PRIVILEGES;

Query Cache

If swap between different MySQL versions, cache may cause problem. For example, they may use the different end character. Therefore, need to flush cache.

#To check whether the query cache is present in your MySQL server
mysql> SHOW VARIABLES LIKE 'have_query_cache';

#To monitor query cache performance
mysql> SHOW STATUS LIKE 'Qcache%';

#removes all query results from the query cache
mysql> RESET QUERY CACHE ;

Summer