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CHAPTER 5: DATABASE TRANSACTION MANAGEMENT, Dannellia, Dannellia,…

- - - - BATCH TRANSACTION PROCESSING SYSTEM
        
        For enterprises that need to process a large amounts of data using limited resource
        
        Eg: credit card transactions
        
        Where info is collected and stored as a batch. Not processed.
      - ONLINE TRANSACTION PROCESSING SYSTEM (OLTP)
        
        AKA: Real-time transaction processing system
        
        Eg: Online shopping transaction, ATM, PAYPAL
        
        Each transaction processed immediately without delay of accumulating transactions into batch
  - - - JAZRIN
        
        ROW-LEVEL LOCK
        
        The rows locked on by one but the other row is still can be access. This is to prevent race conditions and concurrent database transactions are protected by row-level locking. In this way, real-time tasks can safely share access to a database file, both reading and writing, with little interference.
  - - - backup of all changes made since the last backup
    - - : For example, suppose that you created a full backup on Monday, and used incremental backups for the rest of the week. Tuesday's backup would only contain the data that has changed since Monday. Wednesday's backup would only contain the data that has changed since Tuesday.
    - - Methid if backup where all the files and folders selected for the backup will be backed up.
    - - Differential Backup
        
        Backup of changes since last full backup.
        Full backup done first and subsequent backup runs, changes made since last full backup.
        
        Example of Differential Backup
        
        Suppose for example that you wanted to create a full backup on Monday and differential backups for the rest of the week.
        Tuesday's backup would contain all of the data that has changed since Monday. It would therefore be identical to an incremental backup at this point.
        On Wednesday, however, the differential backup would backup any data that had changed since Monday.
        Monday (last full)---> Tuesday (saved from Monday backup)
        ----->Wednesday(still data contained changed from Monday)
  - - - Avoids the rolling back of conflicting transactions by requiring that locks be obtained in succession.
      - The serial lock assignment required in deadlock avoidance increases action response times.
      - Must obtain all of the locks it needs before it can be executed.
- - - - ISOLATED/ ISOLATION pg.12
        
        transactions do not interfere with each other except in allowable ways.
        
        The transaction may be restricted from interfering in other ways such as not viewing the temporary changes made by other transactions.
        
        FOR EXAMPLE :
        if a transaction T1 is being executed and is using data item X, that data item cannot be accessed by any other transaction (T2…Tn) until T1 ends.
  - - - Growing phase, in which a transaction acquires all the required locks without unlocking any data.
        
        Shrinking phase, in which a transaction releases all locks and cannot obtain any new lock.
- - - - occurs when one transaction reads data written by another transaction before the other transaction commits.
        
        is also known as a dirty read because it is caused by one transaction reading dirty (uncommitted) data.
        
        Violates the isolation property of transaction.
      - FIELD-LEVEL LOCK
        
        Allows concurrent transactions to access the same row if they require the use of different fields with that row.
        
        Most flexible lock buy requires an extremely high level of overhead.
        
        EXAMPLE OF CRITICAL EVENTS
        
        Hardware/software failures
        
        A failure of this type could be a hard disk media failure, a bad capacitor on a motherboard, or a failing memory bank.
        
        Other causes of errors under this category include application program or operating system errors that cause data to be overwritten, deleted, or lost.
        
        Human-caused incidents
        
        categorized as unintentional or intentional.
        
        An unintentional failure is caused by a careless end user. Such errors include deleting the wrong rows from a table,
        pressing the wrong key on the keyboard, or shutting down the main database server by accident.
        
        Intentional events are of a more severe nature and normally indicate that the company data is at serious risk.
        Under this category are security threats caused by hackers trying to gain unauthorized access to data resources and virus attacks caused by individuals trying to compromise the database operation and damage the company.
        
        Natural disasters
        
        fires, earthquakes, floods, and power failures.
- - - - 1. read(A)
        2. A := 50
        3. write(A)
        4. read(B)
        5. B := B + 50
        6. write B
        
        consistency requirement
        
        the sum of A and B is unchanged by the execution of the transaction
        
        atomicity requirement
        
        if the transaction fails after step 3 and before step 6, the system should ensure that its updates are not reflected in the database, else an inconsistency will result.
- - - - (refer to slide 54)
      - on time 0, both data X and data Y is still unlocked
        
        on time 1, transaction 1 locked data X while data Y is still unlocked
        
        on time 2, transaction 2 locked data Y
        
        on time 3, transaction 1 want to lock data Y but apparently data Y is locked by transaction 2 so transaction 1 status is waiting
        on time 4, transaction 2 want to lock data X but data X is locked by transaction 1 so transaction 2 is also waiting
        
        apparently, both transactions are waiting for each other and this lead to deadlock
- - - - Inconsistent retrievals occur when a transaction accesses data before and after another transactions finish working with such data.
      - For example, an inconsistent retrieval would occur if transaction T1 calculated some summary (aggregate) function over a set of data while another transaction (T2) was updating the same data.
- - - - One in which all data integrity constraints are satisfied
    - - The equivalent of a single SQL statement in an application program or transaction
    - - A transaction might consist of one or more data-manipulation statements and queries, each reading and/or writing information in the database.
        
        Example: SELECT, UPDATE and INSERT statement.
  - - - In this situation only one transaction can do the transaction first which is T1 and T2 have to wait until the T1 finish it transaction. This is to prevent the data from being miscalculated.
- - - - COMMIT statement is reached
      - ROLLBACK statement is reached
      - End of program is reached
      - Program is abnormally terminated
- - - - Writes all of its updated buffers in memory to disk.
        
        It does not execute any other requests while the operation is running.
        
        A checkpoint operation is also registered in the transaction log.
        
        The physical database and the transaction log will be in sync.
        
        Synchronization is required.
- - - - When the locked point is reached, the data are modified to conform to the transaction requirements.
        
        Lastly, the transaction is completed as it releases all of the locks it acquired in the first phase.
- - - - Critical events:
        
        hardware/software failures
        
        human-caused incidents
        
        natural disasters.