A real-time database system is a database where timely responses to user requests are needed. There are hard and soft real-time database systems. A real-time database uses main memory for faster access and retrieval of data. Transactions must meet deadlines and indexing is done using T-trees to efficiently store and retrieve data from main memory. The Adaptive Earliest Deadline scheduling algorithm is used to manage large volumes of transactions in real-time databases.

1. REAL TIME DATABASE

2. A real-time database system is a database system
in which a timely response to a user request is
needed

3. Types of Real-Time Database Systems
• Hard real-time database systems, e.g. early warning
system
• Soft real-time database systems, e.g., banking system,
airline reservation system, digital library, stock market
etc.

4. TRANSACTION
• It is said to be set of read or write operations.
QUERY
• A transaction is said to be a query if it contains either
a read or update operation.
• Commit is a point of no return, once a transaction is
commited we are certain that, the changes to the
database are permanent.

5. ACID PROPERTIES

6. ACID PROPERTIES
A- ATOMICITY
C- CONSISTENCY
I-ISOLATION
D- DURABILITY

7. ACID PROPERTIES
ATOMICITY
Atomicity requires that each transaction is "all or nothing": if one part of
the transaction fails, the entire transaction fails, and the database state is
left unchanged.
CONSISTENCY
The consistency property ensures that any transaction will bring the
database from one valid state to another. Any data written to the database
must be valid according to all defined rules.

8. ISOLATION
Until and unless a transaction is commited, the actions of it are not visible
to any other transactions
DURABILITY
Durability means that once a transaction has been committed, it will
remain so, even in the event of power loss, crashes, or any errors.

9. QUERIES IN REALTIME DATA BASE
SYSTEM
• The queries associated with a RTDBS are associated with a
deadline, there may be some response after the queries passed the
deadlines.
•The data returned in response to a query must have absolute and
relative consistency
ABSOLUTE CONSISTENCY
It is accuracy. The data returned in response to a query must be
close to the result expected. Ex. If temperature or pressure is interrogated in
a chemical vessel the data returned to be close to the current temperature or
pressure.
RELATIVE CONSISTENCY
In case of multiple data is to be collected, it must be close to each
other.

10. MEMORY FOR RTDBS
MAIN MEMORY
•The entire database is residing on the main memory is
the concept behind main memory databases
•Main memory databases are faster than disk based
databases. Since accessing data in memory reduces the I/
O reading activity when querying the data which provides
faster and more predictable performance than disk

11. Many MMDBs add durability via the following mechanisms
•Snapshot files or checkpoint images which record the state of the
database at a given moment in time.
•Transaction logging, which records changes to the database in a file
and facilitates easy recovery
•Non-volatile random access memory (NVRAM), usually in the form of
static RAM backed up with battery power or an electrically erasable
programmable ROM (EEPROM). With this storage, the MMDB
system can recover the data stored from its last consistent state upon
reboot.
•A clone database is created, which can be used when the primary
database crashes.

13. DEADLOCK CONDITION

14. DEAD LOCK CONDITION IN DATABASE
•There may be situations when two or more transactions are put into wait state
simultaneously .
•In this position each would be waiting for the other transaction to get released.
•EXAMPLE
Suppose we have two transactions 1 and 2 both executing simultaneously.
The transaction 1 is to update student table and then update course table.
The transaction 2 is to update course table and then student table.
•When a table is updated by a transaction it is locked for preventing access from other
transaction.
•In the example both transaction 1 and 2 lock student and course table respectively,
so both are locked.
•The two transactions should be executed simultaneously, so each one waits for other
and causing a deadlock.

15. DEAD LOCK REMOVAL IN RTDBS
•If a deadlock cycle is detected, one of the transactions involved in the cycle must
be aborted in order to break the cycle.
•In a RTDB system, the victim transaction should be chosen such that the largest
number of remaining transactions can meet their deadline
•Five deadlock resolution policies that take into account the timing properties of the
transactions and the cost of abort operations have been given. They are
Always aborts the transaction invoking deadlock detection.
Trace the deadlock cycle, and abort the transaction with the
furthest deadline.
Trace the deadlock cycle, abort the transaction with the earliest
deadline.

16. Trace the deadlock cycle, and abort the transaction with the least
criticalness.
Abort the infeasible transaction with the least criticalness. If all
transactions are feasible, then abort a feasible transaction with the least
criticalness.

17. T TREE INDEXING
•A T-tree is a balanced index tree data structure optimized for cases where both
the index and the actual data are fully kept in memory
•The actual data is always in main memory together with the index so that they just
contain pointers to the actual data fields.
•A T-tree node usually consists of pointers to the parent node, the left and right
child node, an ordered array of data pointers and some extra control data

18. TTREE STRUCTURE

19. SEARCH
•Search starts at the root node
•If the current node is the bounding node for the search value
then search its data array. Search fails if the value is not found
in the data array
•If the search value is less than the minimum value of the
current node then continue search in its left subtree. Search
fails if there is no left sub tree
•If the search value is greater than the maximum value of the
current node then continue search in its right subtree. Search
failes if there is no right sub tree

20. ALGORTHIM USED IN REAL TIME DATABASE
.
•Most of the transactions in the real time DB are associated with a deadline,
hence Earliest Deadline First (EDF) algorithm finds a greater solution to
schedule those transactions. But EDF algorithm will be working efficiently if
the number of transactions are moderate. But usually the DB transactions
are huge in a systems and EDF may not be suitable which leads to
congestion.
•To manage with huge transactions an algorithm called Adaptive Earliest
Deadline (AED) is implemented. It uses the congestion control and can
process huge number of transactions. It uses two groups HIT and MISS
group.
Each transaction associated with deadline are put in HIT group
Transaction not having deadline are put in MISS group
First the HIT group transaction will be executed and then the MISS
group transaction will be executed

21. Ex
In a flight cockpit the cabin temperature, pressure, humidity should be monitored
continuously
In a flight other things such as entrainment system, air-conditioning system are also to
be monitored
But they are not much important as cockpit status. So the earlier one is put in HIT
group and the latter one is put in MISS group

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