Lost Update problem

Question

IN these questions , in T1  it will read value  of A from hard disk or local buffer and W(A) when execute it will make change in local buffer or hard disk , are w(A) and commit are same because commit means we stored data in hard disk anyone explain plz in detail

Comments

@Bikram  sir plz explain

Answer 1

commit and w(a) are not same

w(a) means saving data somewhere(hard disk or local buffer) but if system fails that data is loss, but commit means saving as well as making an entry in log record  of database and replicating value in all servers throughout network so just in case there is failure in any of servers it copy will exist. also unless commit if performed there is no guarantee that ACID property will be maintained.

In simple word commits means changes performed are permanent and W(a) means change is temporary.

Example

Suppose there is only one transaction, you want to someone Rs 100 form your bank account, money has been deducted from your account, and successfully reached to person account, but if this transaction is not committed both you and another person won't see any change in your account. as soon as transaction is successfully committed both will have new updated balance in account

Comments

w(A) it wil update in local buffer . It is temporary changes.

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ohh okk commit will store it in hard disk permanently am i right

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Yes, right..if it is commit then it store in hard disk permanently .