Magnetic disk is the secondary storage device used to support direct access to a desired location.Parts in Magnetic diskThe different parts that are present in magnetic disk or hard disk are explained below. All these parts are helpful to read, write and store the data in the hard disk.Disk blocks − The unit data transfer between disk and main memory is a block. A disk block is a contiguous sequence of bytes.Track − Blocks are arranged in concentric rings called tracks.Sectors − A sector is the smallest unit of information that can be read from or written to disk: for ... Read More

Shadow paging is one of the techniques that is used to recover from failure. We all know that recovery means to get back the information, which is lost. It helps to maintain database consistency in case of failure.Concept of shadow pagingNow let see the concept of shadow paging step by step −Step 1 − Page is a segment of memory. Page table is an index of pages. Each table entry points to a page on the disk.Step 2 − Two page tables are used during the life of a transaction: the current page table and the shadow page table. Shadow ... Read More

All data items are updated at the end of the transaction, at the end, if any data item is found inconsistent with respect to the value in, then the transaction is rolled back.Check for conflicts at the end of the transaction. No checking while the transaction is executing. Checks are all made at once, so low transaction execution overhead. Updates are not applied until end-transaction. They are applied to local copies in a transaction space.PhasesThe optimistic concurrency control has three phases, which are explained below −Read PhaseVarious data items are read and stored in temporary variables (local copies). All operations ... Read More

The timestamp-ordering protocol ensures serializability among transactions in their conflicting read and write operations. This is the responsibility of the protocol system that the conflicting pair of tasks should be executed according to the timestamp values of the transactions.A conflict occurs when an older transaction tries to read/write a value already read or written by a younger transaction. Read or write proceeds only if the last update on that data item was carried out by an older transaction.Otherwise, the transaction requesting read/write is restarted and gives a new timestamp. Here no locks are used so no deadlock.The timestamp of transaction ... Read More

There are three possible ways in which a transaction can be executed. These are as follows −Serial execution − In serial execution, the second transaction can begin its execution only after the first transaction has completed. This is possible on a uniprocessor system.Parallel execution − In parallel execution, two transactions can start their execution at exactly the same instant of time. For this, we require more than one processor.Concurrent execution − In concurrent execution, execution of the second process can begin even before the process has completed its execution.Let us consider two transactions T1 and T2. In concurrent execution, the ... Read More

Use the create command to create a table. Insert the values that are book information into the created database table using insert command.If we want to view or retrieve the inserted data use the select command.Step 1Create a book table in database as follows −The create command is used to create table, view, indexSyntaxThe syntax for the create command is as follows −Create table tablename(col1 datatype(size), col2 datatype(size), ……….colN datatype(size));ExampleUse the below mentioned command −create table book (bookname varchar(30), authorname varchar(30), noofcopies number(20));The output is the table created as shown below −BooknameAuthornamenoofcopiesStep 2Describe − The command used to describe the ... Read More

Locking and unlocking of the database should be done in such a way that there is no inconsistency, deadlock and no starvation.2PL locking protocolEvery transaction will lock and unlock the data item in two different phases.Growing Phase − All the locks are issued in this phase. No locks are released, after all changes to data-items are committed and then the second phase (shrinking phase) starts.Shrinking phase − No locks are issued in this phase, all the changes to data-items are noted (stored) and then locks are released.Consider a tree structure database as follows −A -> B -> CLet us now ... Read More

Locking and unlocking of the database should be done in such a way that there is no inconsistency, deadlock, and no starvation.2PL locking protocolEvery transaction will lock and unlock the data item in two different phases.Growing Phase − All the locks are issued in this phase. No locks are released, after all changes to data-items are committed and then the second phase (shrinking phase) starts.Shrinking phase − No locks are issued in this phase, all the changes to data-items are noted (stored) and then locks are released.The 2PL locking protocol is represented diagrammatically as follows −In the growing phase transaction ... Read More

A materialized view is a view whose contents are computed and stored. Materialized view is also a logical virtual table, but in this case the result of the query is stored in the table or the disk. The performance of the materialized view is better than normal view since the data is stored in the disk.It's also called indexed views since the table created after the query is indexed and can be accessed faster and efficiently.ExampleConsider the view given below −Create view branchloan(branch-name, total-loan) as select branch-name , sum(amount) from loan groupby branch-name;Materializing the above view would be especially useful ... Read More

Let’s see the stages of database system life cycle (DDLC) and their facts using tabular form −Stage of Database system development LifecycleExample of FactsExample of Documentation ProducedDatabase PlanningAims and objectives of database projects.Mission statements and objectives.System IdentificationDescription of major user views (Job roles, business application areas).Definition of scope and boundary of database system, definition of user views to be supported.Requirements Collection and AnalysisRequirements of user views, system specifications, including performance and security requirements.User requirement specification, system specification.Database designUser’s responses to checking the logical database design, functionality provided by target DBMS.Logical database design, data dictionary, physical database design.Application DesignUsers’ response to ... Read More