Question

[Distributed Systems] Which of the following tasks is not easily parallelizable? Counting the frequency of words in a collection of text files Querying a read-only database Identifying major geographical features on a satellite map Booking airline tickets for thousands of customers I don't know [OS] On most modern filesystems, what happens when your program attempts to open a non-existent file without any protections?* The program is terminated by an exception The program is terminated by a segmentation fault The OS filesystem creates an empty file at the specified path The OS writes an I/O error to its syscall log and allows the program to continue I don't know

Answer 1

A.

The correct option is

Booking airline tickets for thousands of customers.

This is because the tickets are limited, and we need to keep track of the current number of tickets issued and remaining. So, some form of synchronization, to update shared variables like remaining_tickets, would need to be maintained after EVERY transaction by every thread.

Regarding other options :

• Counting the frequency of words in a collection of text files
  • Here, each text file is static, and may be processed independently and parallely, and then the results can be combined once at end.
• Querying a read-only database
  • Read-only database is static, so multiple read-transactions can be carried out parallely by multiple threads safely.
• Identifying major geographical features on a satellite map
  • ​​​​​​​Geographical locations are static (or at least change so slowly to be hardly noticeable in a short time). So separate areas may be identified parallely, and then results can be combined once at end.

B.

The correct option is

The OS filesystem creates an empty file ar the specified path.

Regarding other options :

• The program is terminated by an exception
  • ​​​​​​​This happens when a program runs into undefined/unrecoverable statw, eg. division by zero.
• The program is terminated by a segmentation fault
  • ​​​​​​​This happens when programs tries to access protected memory, eg. writing to a read-only memory-segment.
• The OS writes an I/O error to its syscall log and allows the program to continue
  • ​​​​​​​This is very, very, very unlikely, as result of any user-operation (here, opening a file) must be passed to the user. All POSIX APIs adhere to this.