RAID, Redundant Array of Inexpensive Disks, used to provide fault tolerance to database servers. We have 0 through 5 RAID levels that offers different levels of performance and fault tolerance.
RAID controller is used when one drive fails and the other is still running well. The controller will automatically rebuild the data from the other devices and restores the same to the crashed system. Hence the RAID controller technology, depending on the importance of the data, is used to restore the data automatically from the other systems.
RAID is a mechanism of storing the same data in different locations. Since the same data is stored, it is termed as redundant. The data is stored on multiple disks which improves performance. The drive's storage is divided into units ranging from a sector (512 bytes) up to several megabytes. This is termed as disk stripping.
There are NINE types of RAID plus an additional non-redundant array (RAID-0). However, RAID levels 0, 1, and 5 are the most commonly found.
► RAID 0: This level does involve stripping but no redundancy of data. Offers the best performance at the cost of NO fault tolerance.
► RAID 1: This level is termed as data mirroring consisting of at least two drives that duplicate the storage of data. No stripping involved. Often used for multi user system for best performance and fault tolerance.
► RAID 2: It involves stripping with some disks storing error checking and correcting (ECC) information.
► RAID 5: Consists of 3 or more disks in a way that protects data against loss of any one disk.
► RAID 6: Has stripped disks with dual parity.
► RAID 10: uses both striping and mirroring.
► RAID 53: Merges the features of RAID level 0 and RAID level 3
Stored procedures manage, control and validate data.
Large queries can be avoided.
Reduces network traffic since they need not be recompiled.
Even though the stored procedure itself may be a complex piece of code, we need not write it over and over again. Hence stored procedures increases reusability of code
Permissions can be granted for stored procedures. Hence, increases security.
Stored procedures provide performance benefits through local storage, precompiling the code, and caching.
Stored procedures offers security features that includes encryption and privilege limits that restrict users from modifying structure of stored procedure.
An integer data type can have a variety of IDENTITY values like int, bigint, tinyint etc.
To avoid the integer IDENTITY to run out of scope, BIGINT should be used as the data type or DECIMAL (38,0)
CREATE TABLE sample_t ( col1 BIGINT IDENTITY(-9223372036854775808, 1) )
► Column with identity property contains unique system generated value in the table.
► Column with identity property is similar to AutoNumber field in MS Access.
► You can set start and increment value while setting column property to identity.
► Column with identity property contains unique values within the table.
► The column with uniqueidentifier property contains globally unique data.
► SQL server uses uniqueidentifier property for merge replication.
► Same like Identity Column, SQL server supports uniqueidentifier column that also contains system generated value.
► A column or local variable of uniqueidentifier data type can be initialized using NEWID function.
Cursors behavior can be controlled by dividing them into cursor types: forward-only, static, keyset-driven, and dynamic. SQL server supports keywords SCROLL and INSENSITIVE to define cursor behavior in terms of scrollability and sensitivity.
► Truncate command is used to remove all rows of the column.
► The removed records are not recorded in the transaction log.
► It is the fast way to remove all the records from the table.
► The records once removed can't be rolled back.
► It can't activate trigger.
► It resets the identity of the column.
Delete command removes records one at a time and logs into the transaction log.
It can be used with or without where clause.
The records can be rolled back.
It activates trigger.
It doesn't reset the identity of the column.
The following is the process for Unzip a file in SSIS.
► Use Execute Process Task in the Control Flow Task.
► From BIDS, drag and drop an Execute Process Task to the control flow and configure.
In the Execute Process, perform the following configurations:
► Executable: The path of the application that is being used.
► Arguments: Need to supply the arguments to extract the zipped files. -o+ is the default parameter for overwriting files if they exist.
► Working Directory: The current directory for all process.