Schedule in DBMS

MCA, MSc(CS), PGDCA
Pratibha Rashmi

 A schedule contains a set of instruction
which specify the order of the execution of
the instructions.
 It could be three types.
dbrau
Schedule
Serial Schedule
Non-Serial
Schedule
Serializable
Schedule

 The serial schedule is a type of schedule where
one transaction is executed completely before
starting another transaction.
 A serial schedule doesn’t allow concurrency, only
one transaction executes at a time and the other
starts when the already running transactionstarts when the already running transaction
finished.
 If there are two transactions T1 and T2
which have some operations. If it has no
interleaving of operations, then there are
the following two possible results:

 Execute all the operations of T1 which was
followed by all the operations of T2.
 Here, Schedule A shows the serial schedule
where T1 followed by T2.

 Execute all the operations of T2 which was
followed by all the operations of T1.
 Here, Schedule A shows the serial schedule
where T2 followed by T1.

 If interleaving of operations is allowed, then
there will be a non-serial schedule.
 There are many possible orders in which the
system can execute the individual operations
of the transactions.of the transactions.
 If there are two transactions T1 and T2
which have some operations. If it has no
interleaving of operations, then there are
the following two possible results:

 Schedule C and Schedule D are the non-serial
schedules. Because It has interleaving of
operations.

 A serializable schedule always leaves the
database in consistent state. A serial
schedule is always a serializable schedule.
 However, a non-serial schedule needs to be
checked for Serializability.checked for Serializability.
 A transaction schedule is serializable if its
outcome is equal to the outcome of its
transaction executing serially.

 Let us consider I1 and I2 are two consecutive
instructions of T1 and T2 respectively. Both the
instruction are operating on same data item Q, these
instruction are said to be conflicting instruction if any
one of the following instruction occurs
simultaneously.
 I1 = read(Q) & I2 = write(Q) I1 = read(Q) & I2 = write(Q)
 I1 = write(Q) & I2 = read(Q)
 I1 = write(Q) & I2 = write(Q)
It means in both the instruction one operation is
write operation on the same data item leads to the
conflicts.
 Conflicting instruction can not be swap(interchange)
otherwise the operation of the schedule will be
change.

 Any execution of a set of transactions is
called as its ___________.
non-serial schedule
serial schedule
scheduleschedule
interleaved schedule
 State true or false: If I = read(Q) and J =
read(Q) then the order of I and J does not
matter.
a) True
b) False

 State true or false: If I = read(Q) and J =
write(Q) then the order of I and J does not
matter.
a) True
b) False
 The _________is a type of schedule where one
transaction is executed completely before
starting another transaction.
a) serial schedule
b) non-serial schedule

 What is scheduling in DBMS?
 What is Schedule list the types of schedule?
What is serial schedule and serializable What is serial schedule and serializable
schedule?
 What do you mean by conflict operations?

 “Fundamentals of Database Systems” by R
Elmasri and S Navathe.
 “An Introduction to Database Systems” by
Bipin Desai
https://www. beginnersbook.com, https://www. beginnersbook.com,
http://Javapoint.com

Schedule in DBMS

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