Verbose GC options

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Admin Uncategorized

Admin Uncategorized song

Profiling Queries with SHOW STATUS


mysql> flush status;
mysql> select SQL_NO_CACHE count(*) from table;

- Check query plan now:

mysql> show status like 'Select%';

- Check engine operations:

mysql> show status like 'Handler%';

- Check if there was any ordering:

mysql> show status like 'Sort%';

- Check how many temporary tables have been created:

mysql> show status like 'Created%';


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Admin MySQL

Is a certain process running your CPU right into the ground? How do you find said process without picking your way through the ps aux results? With this command:

ps -e -o pcpu,cpu,nice,state,cputime,args --sort pcpu | sed '/^ 0.0 /d'

…at which point you can kill it with sudo kill -9.

Admin Linux, Unix ps

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./mysqld_safe --user=mysql --basedir=/usr/local/mysql-5.0.67-linux-x86_64-icc-glibc23
--ledir=/usr/local/mysql-5.0.67-linux-x86_64-icc-glibc23/bin --mysqld=mysqld

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./mysqladmin ext -u root -p -ri60
./mysqladmin ext -u root -p -ri60 | grep tmp

Admin Linux, MySQL Upgrade MySQL

mysql> FLUSH STATUS;

mysql> SELECT COUNT(*) FROM TABLE;

Admin MySQL performance

Procedure to add a swap file

You need to use dd command to create swapfile. Next you need to use mkswap command to set up a Linux swap area on a device or in a file.

a) Login as the root user

b) Type following command to create 512MB swap file (1024 * 512MB = 524288 block size):

# dd if=/dev/zero of=/swapfile1 bs=1024 count=524288

c) Set up a Linux swap area:

# mkswap /swapfile1

d) Activate /swapfile1 swap space immediately:

# swapon /swapfile1

e) To activate /swapfile1 after Linux system reboot, add entry to /etc/fstab file. Open this file using text editor such as vi:

# vi /etc/fstab

Append following line:

/swapfile1 swap swap defaults 0 0

So next time Linux comes up after reboot, it enables the new swap file for you automatically.

g) How do I verify swap is activated or not?

Simply use free command:

$ free -m

Admin Linux swap

vi first  edit source file
then move your cursor to start of selection
ma       mark current position with letter a
then move your cursor to end of selection
y'a     yank to buffer x from current position to mark a
:e other  edit target file
move cursor to where you want the data
p       put from buffer x

Admin Linux

Constructors

When you create a new instance (a new object) of a class using the new keyword, a constructor for that class is called. Constructors are used to initialize the instance variables (fields) of an object. Constructors are similar to methods, but with some important differences.

• Constructor name is class name. A constructors must have the same name as the class its in.
• Default constructor. If you don’t define a constructor for a class, a default parameterless constructor is automatically created by the compiler. The default constructor calls the default parent constructor (super()) and initializes all instance variables to default value (zero for numeric types, null for object references, and false for booleans).
• Default constructor is created only if there are no constructors. If you define any constructor for your class, no default constructor is automatically created.
• Differences between methods and constructors.
  • There is no return type given in a constructor signature (header). The value is this object itself so there is no need to indicate a return value.
  • There is no return statement in the body of the constructor.
  • The first line of a constructor must either be a call on another constructor in the same class (using this), or a call on the superclass constructor (using super). If the first line is neither of these, the compiler automatically inserts a call to the parameterless super class constructor.

  These differences in syntax between a constructor and method are sometimes hard to see when looking at the source. It would have been better to have had a keyword to clearly mark constructors as some languages do.

• this(...) – Calls another constructor in same class. Often a constructor with few parameters will call a constructor with more parameters, giving default values for the missing parameters. Use this to call other constructors in the same class.
• super(...). Use super to call a constructor in a parent class. Calling the constructor for the superclass must be the first statement in the body of a constructor. If you are satisfied with the default constructor in the superclass, there is no need to make a call to it because it will be supplied automatically.

Admin J2EE Constractor

To copy a block of text between files execute the commands:

Admin Linux vi