TRANSACTION STATES
This video discusses different states in a transaction. It moves from one state to the other as it entries the system to be executed.
A transaction must be in one of the following states:
Active State
· This is the initial state in the life cycle of a transaction.
· A transaction is called in an active state as long as its instructions are getting executed.
· All the changes made by the transaction now are stored in the buffer in main memory.
Partially Committed
· After the last instruction of transaction has executed, it enters into a partially committed state.
· After entering this state, the transaction is considered to be partially committed.
· It is not considered fully committed because all the changes made by the transaction are still stored in the buffer in main memory.
Committed State
· After all the changes made by the transaction have been successfully stored into the database, it enters into a committed state.
· Now, the transaction is considered to be fully committed.
· After a transaction has entered the committed state, it is not possible to roll back the transaction.
· In other words, it is not possible to undo the changes that has been made by the transaction.
· This is because the system is updated into a new consistent state.
· The only way to undo the changes is by carrying out another transaction called as compensating transaction that performs the reverse operations.
Failed State
· When a transaction is getting executed in the active state or partially committed state and some failure occurs due to which it becomes impossible to continue the execution, it enters into a failed state.
Aborted State
· After the transaction has failed and entered into a failed state, all the changes that were in the local buffer have to be undone.
· To undo the changes made by the transaction, it becomes necessary to roll back the transaction.
· After the transaction has rolled back completely, it enters into an aborted state,
· At this point, the system has two options:
o Restart the Transaction
o Kill the transaction.
This channel has the videos for the below given topics:
UNIT - I
Database System Applications: A Historical Perspective, File Systems versus a DBMS, the Data Model, Levels of Abstraction in a DBMS, Data Independence, Structure of a DBMS
Introduction to Database Design: Database Design and ER Diagrams, Entities, Attributes, and Entity Sets, Relationships and Relationship Sets, Additional Features of the ER Model, Conceptual Design With the ER Model
UNIT - II
Introduction to the Relational Model: Integrity constraint over relations, enforcing integrity constraints, querying relational data, logical data base design, introduction to views, destroying/altering tables and views.
Relational Algebra, Tuple relational Calculus, Domain relational calculus.
UNIT - III
SQL: QUERIES, CONSTRAINTS, TRIGGERS: form of basic SQL query, UNION, INTERSECT, and EXCEPT, Nested Queries, aggregation operators, NULL values, complex integrity constraints in SQL, triggers and active data bases.
Schema Refinement: Problems caused by redundancy, decompositions, problems related to decomposition, reasoning about functional dependencies, FIRST, SECOND, THIRD normal forms, BCNF, lossless join decomposition, multi-valued dependencies, FOURTH normal form, FIFTH normal form.
UNIT - IV
Transaction Concept, Transaction State, Implementation of Atomicity and Durability, Concurrent Executions, Serializability, Recoverability, Implementation of Isolation, Testing for serializability, Lock Based Protocols, Timestamp Based Protocols, Validation- Based Protocols, Multiple Granularity, Recovery and Atomicity, Log–Based Recovery, Recovery with Concurrent Transactions.
UNIT - V
Data on External Storage, File Organization and Indexing, Cluster Indexes, Primary and Secondary Indexes, Index data Structures, Hash Based Indexing, Tree base Indexing, Comparison of File Organizations, Indexes and Performance Tuning, Intuitions for tree Indexes, Indexed Sequential Access Methods (ISAM), B+ Trees: A Dynamic Index Structure.