Script to Get Available and Free Disk Space for SQL Server

Problem
Often we face the situation where we need to check the total disk space and available disk space for both physical and LUN/Mount drives. The extended stored procedure XP_FixedDrives is unable to help us in this scenario, so we have to log into the machine to check the total and free disk space for each physical/LUN/mount drive. In this tip, I show how this can be done using PowerShell.

Solution
http://www.mssqltips.com/tip.asp?tip=2444

Difference between temporary table and table variable

Temporary TablesThere are two types of temporary tables:

Local Temporary Table: Local temporary tables are visible only to their creators during the same connection to an instance of SQL Server as when the tables were first created or referenced. Local temporary tables are deleted after the user disconnects from the instance of SQL Server

You can create local temporary table adding # sign again the table name

Global Temporary Table: Global temporary tables are visible to any user and any connection after they are created, and are deleted when all users that are referencing the table disconnect from the instance of SQL Server.

You can create global temporary table adding ## sign again the table name

What are the things you can do with the temporary tables?
-Add/drop constraints except foreign key
-You can perform DDL statements (Alter, Drop)
-Create clustered and non-clustered indexes
-Use identity columns
-Use it in transaction and it support transaction
-Perform any DML operations (SELECT, INSERT, UPDATE, DELETE)
-Create the table with same name using different session; make sure constraint name must be different in the table.

[sourcecode language="sql"]
-- Adding the constraint primary key and unique key
-- constraint will create the cluster and non-cluster index
create table #temptbl
(id int identity (100,1) Primary key,
data varchar(20) constraint UK Unique
)

insert into #temptbl values ('Jugal')
insert into #temptbl values ('Jugal1')
insert into #temptbl values ('Jugal2')

select * from #temptbl
sp_help #temptbl

--Adding column to existing temporary table
alter table #temptbl
Add Name varchar(20) null

-- Modifying column
alter table #temptbl
alter column name varchar(30)

--adding index
create nonclustered index UK2 on #temptbl (name)

--checking indexes
sp_helpindex #temptbl

-- Supports transaction
begin tran
insert into #temptbl values('sqldbpool','sqldbpool')
rollback

select * from #temptbl

--Checking for the foreign key
create table #temptbl1
(
id int constraint FK1 references #temptbl1(id),
value int
)
--Skipping FOREIGN KEY constraint 'FK1' definition for temporary table. FOREIGN KEY constraints are not enforced on local or global temporary tables.

insert into #temptbl1 values(2000,10)

--DML Opertaions
select * from #temptbl

update #temptbl set data = 'SQLDBPool'
where id = 100

select * from #temptbl

delete from #temptbl where id = 101

select * from #temptbl
--dropping temporary table
drop table #temptbl
[/sourcecode]

Table variableThe syntax for creating table variables is quite similar to creating either regular or temporary tables. The only differences involve a naming convention unique to variables in general, and the need to declare the table variable as you would any other local variable in Transact SQL. Life span of the table variable is limited to life of the transaction. You can only create the cluster index on table variable.

[sourcecode language="sql"]
-- creating table variable
declare @var table
(id int identity(100,1) primary key,
data varchar(20) default 'hi'
)

--Checking DML Statement --working fine
insert into @var values('jugal')
insert into @var values('sqldbpool')
delete from @var where id = 100
update @var set data = 'sqldbpool-1' where id = 101
select * from @var


-- Checking transaction support/doesn't support transaction
begin tran
declare @var table
(id int identity(100,1) primary key,
data varchar(20) default 'hi'
)

insert into @var values('jugal')
insert into @var values('sqldbpool')
insert into @var values (DEFAULT)
delete from @var where id = 100
update @var set data = 'sqldbpool-1' where id = 101

rollback
select * from @var
-- Checking alter failed/doesn't support DDL
alter table @var
alter column data varchar(30)

alter table @var
Add Name varchar(20) null
[/sourcecode]

Similarities between temporary tables and table variable:- Both are created in tempdb
- You can create constraint like primary key, default and check on both but the table variable has certain limitation for the default and check constrain where you can not use UDF
- Clustered indexes can be created on table variables and temporary tables
- Both are logged in the transaction log but the tempDB recovery model is SIMPLE, log will be truncated once the trasaction get complete.
Just as with temp and regular tables, users can perform all Data Modification Language (DML) queries against a table variable: SELECT, INSERT, UPDATE, and DELETE.

Differences
- You can not create non-cluster index and statistics on table variable but you can create it on temporary table.
- You can not use DDL statement on table variable but you can use it on temporary table.
- Table variable doesn't support transaction wheras temporary table supports.

MySQL Replication Setup

Mysql uses a Master-slave/Publisher-Subscriber model for Replication. MySQL replication is an asynchronous replication. In MySQL replication master keeps a log of all of the updates performed on the database. Then, one or more slaves connect to the Master(Publisher Server), read each log entry, and perform the indicated update on the slave (Subscriber) server databases. The master server is responsible for the track of log rotation and access control.

Each slave server has to keep the track of current position within the server's transaction log. As new transactions occur on the server, they get logged on the master server and downloaded by each slave. Once the transaction has been committed by each slave, the slaves update their position in the server's transaction log and wait for the next transaction.

In this article, I will show you the steps to configure the Master/Slave replication between two servers.

Step 1: Create a user on Master server which Slave server can use to connect. I have created the user named "repl_user".
[sourcecode language="sql"]
--Connect to MySQL Master server
mysql -u root -proot
--Execute the below code
GRANT REPLICATION SLAVE ON *.* TO 'repl_user'@'%' IDENTIFIED BY 'password';
FLUSH PRIVILEGES;
[/sourcecode]

Step 2: We have to change the MySQL configuration file usually in the /etc/mysql.cnf location. Here we will add the replication configuration parameters.

log-bin – will be used to write a log on the desired location
binlog-do-db – will be used to enabled the database for writing log. I have used Publisher_Database, you have to specify your database name.
server-id – Specify the ID of the Master server

[sourcecode language="sql"]
log-bin = /home/mysql/logs/mysql-bin.log
binlog-do-db=publisher_database
server-id=1
[/sourcecode]

Step 3: Once you have added the above configuration parameters into the My.cnf, next step is restart the MySQL Master Instance.
You can use below command to restart the MySQl service.
[sourcecode language="sql"]
/etc/init.d/mysqld restart
service mysqld restart
[/sourcecode]

Step 4: We have to configure the /etc/my.cnf file on the slave server. Here we will add the below parameters in the configuration file.

server-id - gives the Slave its unique ID
master-host - tells the Slave the I.P address of the Master server for connection. You can get the IP address using IPConfig command.
master-connect-retry - Here we will specify the connection retry interval.
master-user - Specify the user which has permission access the Master server
master-password - Specify the password of the replication user mentioned above
replicate-do-db - Specify the subscriber database name
relay-log - direct slave to use relay log

[sourcecode language="sql"]
server-id=2
master-host=128.20.30.1
master-connect-retry=60
master-user=repl_user
master-password=password
replicate-do-db=subscriber_slave
relay-log = /var/lib/mysql/slave-relay.log
relay-log-index = /var/lib/mysql/slave-relay-log.index
[/sourcecode]

Step 5: Restart the slave MySQl instance
[sourcecode language="sql"]
/etc/init.d/mysqld restart
service mysqld restart
[/sourcecode]

Step 6: If your Master MySQL instance is live instance, you have to do the backup/restore using MySQLDump utility.
[sourcecode language="sql"]
--Connect to MySQL Master server
mysql -u root -proot

--Stop the write operation
FLUSH TABLES WITH READ LOCK;

--Generate the dump of the database (backup)
--gzip command will compress the file and create the zip file name backup.sql.gz
mysqldump publisher_master -u root -p > /home/my_home_dir/backup.sql;
gzip /home/my_home_dir/backup.sql;

--execute below copy command on slave to copy the backup file
scp root@128.20.30.1:/home/my_home_dir/database.sql.gz /home/my_home_dir/

--Once copied, extract the file using gunzip
gunzip /home/my_home_dir/backup.sql.gz

--restore the databsae
mysql -u root -p subscriber_slave </home/my_home_dir/backup.sql

[/sourcecode]

Step 7: Execute the SHOW MASTER STATUS command on Master server. It will give you the bin log file name and position which we will use specify the slave.
[sourcecode language="sql"]
SHOW MASTER STATUS;
[/sourcecode]

+------------------+----------+--------------+------------------+
| File | Position | Binlog_Do_DB | Binlog_Ignore_DB |
+------------------+----------+--------------+------------------+
| mysql-bin.000001 | 707 | exampledb | |
+------------------+----------+--------------+------------------+


Step 8: Execute the below commands on slave.
[sourcecode language="sql"]
--Connect to MySQL Slave server
mysql -u root -proot
--stop the slave
slave stop;
-- Execute the below command
CHANGE MASTER TO MASTER_HOST='128.20.30.1', MASTER_USER='repl_user', MASTER_PASSWORD='password', MASTER_LOG_FILE='mysql-bin.000001', MASTER_LOG_POS=707;
--Start the Slave
slave start;
[/sourcecode]

Step 9: Login to Master MySQL instance and unlock the tables.
[sourcecode language="sql"]
--Connect to MySQL Master server
mysql -u root -proot
-- unlock the tables if you have executed lock tables command
unlock tables;
[/sourcecode]

You are all set. Master to Slave replication has been started. Make sure while configuring the my.cnf file.
1. Take the copy of my.cnf file before starting the replication configuration.
2. Make sure skip-networking parameter is not enabled in the my.cnf file.

T-SQL Script to Check/Create directory

Recently I came across a situation where I need to check whether the directory is exists or not, in case if the directory does not exist, I have to create new one.

As a solution, I have created below script to fix the issue.

[sourcecode language="sql"]
declare @chkdirectory as nvarchar(4000)
declare @folder_exists as int

set @chkdirectory = 'C:\SQLDBPool\SQL\Articles'

declare @file_results table
(file_exists int,
file_is_a_directory int,
parent_directory_exists int
)

insert into @file_results
(file_exists, file_is_a_directory, parent_directory_exists)
exec master.dbo.xp_fileexist @chkdirectory

select @folder_exists = file_is_a_directory
from @file_results

--script to create directory
if @folder_exists = 0
begin
print 'Directory is not exists, creating new one'
EXECUTE master.dbo.xp_create_subdir @chkdirectory
print @chkdirectory + 'created on' + @@servername
end
else
print 'Directory already exists'
GO [/sourcecode]