Suppose a database system crashes again while recovering from a previous crash. Assume checkpointing is not done by the database either during the transactions or during recovery.

Which of the following statements is/are correct?

Consider a linear list based implementation in a file system. Each directory is a list of nodes, where each node contains the file name along with the file metadata, such as the list of pointers to the data blocks. Consider a given directory foo.

Which of the following operations will necessarily require a full scan of foo for successful completion?

A relation r(A, B) in a relational database has 1200 tuples. The attribute A has integer values ranging from 6 to 20, and the attribute B has integer values ranging from 1 to 20. Assume that the attributes A and B are independently distributed. The estimated number of tuples in the output of σ_{(A>10)∨(B=18)}(r) is ______

The following relation records the age of 500 employees of a company, where empNo (Indicating the employee number) is the key:

empAge(empNo, age)

Consider the following relational algebra expression:

π_empNo(empAge ⋈ _(age>age1) ρ_{empNo 1, age1}(empAge))

What does the above expression generate?