DBMS

31. Define page.

The database is partitioned into some number of fixed-length blocks, which are referred to as

pages.

32. Explain current page table and shadow page table.

The key idea behind the shadow paging technique is to maintain two page tables during the life

of the transaction: the current page table and the shadow p age table. Both the page tables are identical when the transaction starts. The current page table may b e changed when a transaction performs a write operation.

33. What are the drawbacks of shadow-paging technique?

Ø Commit Overhead

Ø Data fragmentation

Ø Garbage collection

34. Define garbage collection.

Garbage may be created also as a side effect of crashes. Periodically, it is necessary to find all the garbage pages and to add them to the list of free pages. This process is called garbage

collection.

35. Differentiate strict two phase locking protocol and rigorous two phase locking protocol.

In strict two phase locking protocol all exclusive mode locks taken by a transaction is held

36. How the time stamps are implemented

• Use the value of the system clock as the time stamp. That is a transactio n‟s time stamp is equal

to the value of the clock when the transaction enters the system.

• Use a logical counter that is incremented after a new timestamp has been assigned; that is the

time stamp is equal to the value of the counter.

37. What are the time stamps associated with each data item?

• W-timestamp (Q) denotes the largest time stamp if any transaction that executed WRITE (Q)

successfully.

• R-timestamp (Q) denotes the largest time stamp if any transaction that executed READ (Q)

successfully.