Brief explain how a DBMS handles concurrent execution of transactions
Solution
CONCURENT EXECUTION :
Schedule is a collection of one or more transactions and are executed according to their arrangement in the schedule.Schedule is catogorized into 2 divisions.They are : a)Serial and b) Concurrent
**//First let me introduce you Serial and later explanation on Concurrent Execution//**
a) Serial : An execution of transactions occurs one after the other(one-by-one)
b) Concurrent Execution : It is nothing but an execution of transactions parallelly by sharing the CPU time among them.The database has the chances of containing inconsistence value if the concurrent execution is not considered properly.
Let me explain you with an example,
Consider two transactions T1 and T2 which follows the instructions as below:
T1 :
Read S;
S = S*100;
Write S;
Read F;
F=F/2;
Write F;
T2 :
Read S;
Temp = S * 12;
Read B;
B = B +800;
Write B;
If T2 is a new transaction and suppose B should be deposited with the Rs.800 which is to be deduced from S in Transaction T1.
If we want a serial schedule for Transactions T1 and T2 then either T1 executes before the T2 gets executed or else T1 will execute before T2 is being executed..So now by using Context switching in concurrent Execution Transaction T1 gets executed partially and later T2 also partially.
The following example can support these lines
T1 T2
Read S;
S = S *100;
Write A;
Read S;
Temp = S *12;
Read B;
B = B + Temp;
Write B;
Read F;
F = F /2;
Write F;
As we used Context Switching in this type of Schedule, the 1st one after performing the 3rd line of Transaction T1, and after performing the last statement of T2. T1 first multiplies the amount with 12 with S and writes the new value into S.Later T2 reads the value of S, calculates the value of Temp to be Rs.250(say) and adds the value to B. The leftout part of T1 is executed and Rs.250 is added to B
So it is clear that the correct Context Switching is very important to maintain ACID properties like Atomicity,Consistency,Isolation and Durability.
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Brief explain how a DBMS handles concurrent execution of transactionsS.docx
1. Brief explain how a DBMS handles concurrent execution of transactions
Solution
CONCURENT EXECUTION :
Schedule is a collection of one or more transactions and are executed according to their
arrangement in the schedule.Schedule is catogorized into 2 divisions.They are : a)Serial and b)
Concurrent
**//First let me introduce you Serial and later explanation on Concurrent Execution//**
a) Serial : An execution of transactions occurs one after the other(one-by-one)
b) Concurrent Execution : It is nothing but an execution of transactions parallelly by sharing
the CPU time among them.The database has the chances of containing inconsistence value if the
concurrent execution is not considered properly.
Let me explain you with an example,
Consider two transactions T1 and T2 which follows the instructions as below:
T1 :
Read S;
S = S*100;
Write S;
Read F;
F=F/2;
Write F;
2. T2 :
Read S;
Temp = S * 12;
Read B;
B = B +800;
Write B;
If T2 is a new transaction and suppose B should be deposited with the Rs.800 which is to be
deduced from S in Transaction T1.
If we want a serial schedule for Transactions T1 and T2 then either T1 executes before the T2
gets executed or else T1 will execute before T2 is being executed..So now by using Context
switching in concurrent Execution Transaction T1 gets executed partially and later T2 also
partially.
The following example can support these lines
T1 T2
Read S;
S = S *100;
Write A;
Read S;
Temp = S *12;
Read B;
B = B + Temp;
Write B;
Read F;
F = F /2;
Write F;
3. As we used Context Switching in this type of Schedule, the 1st one after performing the 3rd line
of Transaction T1, and after performing the last statement of T2. T1 first multiplies the amount
with 12 with S and writes the new value into S.Later T2 reads the value of S, calculates the value
of Temp to be Rs.250(say) and adds the value to B. The leftout part of T1 is executed and Rs.250
is added to B
So it is clear that the correct Context Switching is very important to maintain ACID properties
like Atomicity,Consistency,Isolation and Durability.
