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ANSWER If two concurrent transactions access a data item that is being updated by one of them, it is not possible to guarantee that the second will read the correct value. Dirty reads and nonrepeatable reads may occur when one transaction can see intermediate results of another transaction before it as been committed. Given below are two concurrent transactions (bal,) were recorded at times between t, and tg As shown in the table below: If these two transactions interfere with each other, fill in the table below by selecting from the drop down list the values of balance X ( bal,) at specified times between ty and to- Time T1 T 52 " 44 Begin, Transaction Read(bal) bal-bal-10 Write(bal) Commit 12 Begin, Transaction Readibal bal, bal,+100 Write(bal) rollback bal, 100 100 and T2 whose balances of amountx

ANSWER If two concurrent transactions access a data item that is being updated by one of them, it is not possible to guarantee that the second will read the correct value. Dirty reads and nonrepeatable reads may occur when one transaction can see intermediate results of another transaction before it as been committed. Given below are two concurrent transactions (bal,) were recorded at times between t, and tg As shown in the table below: If these two transactions interfere with each other, fill in the table below by selecting from the drop down list the values of balance X ( bal,) at specified times between ty and to- Time T1 T 52 " 44 Begin, Transaction Read(bal) bal-bal-10 Write(bal) Commit 12 Begin, Transaction Readibal bal, bal,+100 Write(bal) rollback bal, 100 100 and T2 whose balances of amountx

Computer Networking: A Top-Down Approach (7th Edition)
Computer Networking: A Top-Down Approach (7th Edition)
7th Edition
ISBN:9780133594140
Author:James Kurose, Keith Ross
Publisher:James Kurose, Keith Ross
Chapter1: Computer Networks And The Internet
Section: Chapter Questions
Problem R1RQ: What is the difference between a host and an end system? List several different types of end...
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Transaction management deals with the problems of always keeping the database in a consistent state even when concurrent accesses and failures occur. Isolation requires that each transaction sees a consistent database at all times and that an executing transaction cannot reveal its results to other concurrent transactions before its commitment. ANSWER If two concurrent transactions access a data item that is being updated by one of them, it is not possible to guarantee that the second will read the correct value. Dirty reads and nonrepeatable reads may occur when one transaction can see intermediate results of another transaction before it has been committed.. Given below are two concurrent transactions T1 and T2 whose balances of amount x (balx) were recorded at times t, between t₁ and tg. As shown in the table below: If these two transactions interfere with each other, fill in the table below by selecting from the drop down list the values of balance X (bal,) at specified times between t₁ and tg. Time T1 [₁ t₂ t3 t4 t5 t6 t7 tg Begin_Transaction Read(baly) baly = baly - 10 Write(baly) Commit T2 Begin_Transaction Read(bal.) bal, = balx + 100 Write(bal.) rollback balx 100 100
Transcribed Image Text:Transaction management deals with the problems of always keeping the database in a consistent state even when concurrent accesses and failures occur. Isolation requires that each transaction sees a consistent database at all times and that an executing transaction cannot reveal its results to other concurrent transactions before its commitment. ANSWER If two concurrent transactions access a data item that is being updated by one of them, it is not possible to guarantee that the second will read the correct value. Dirty reads and nonrepeatable reads may occur when one transaction can see intermediate results of another transaction before it has been committed.. Given below are two concurrent transactions T1 and T2 whose balances of amount x (balx) were recorded at times t, between t₁ and tg. As shown in the table below: If these two transactions interfere with each other, fill in the table below by selecting from the drop down list the values of balance X (bal,) at specified times between t₁ and tg. Time T1 [₁ t₂ t3 t4 t5 t6 t7 tg Begin_Transaction Read(baly) baly = baly - 10 Write(baly) Commit T2 Begin_Transaction Read(bal.) bal, = balx + 100 Write(bal.) rollback balx 100 100
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