CS6223: Distributed Systems

1
CS6223 Distributed Systems

• Review

2
Final Exam

• When and where?
• 7-May-2011, 200pm to 400pm
• LT-9
• What to bring?
• Close Book exam!
• What are the questions?
• Total marks are 100 (2 hours)
• Answer all 6 questions
• How to prepare?
• Understanding lecture notes and tutorial questions

3
Physical Clock Synchronization

• Cristians algorithm
• synchronize clocks with a UTC server

• Berkeley Algorithm
• synchronize a set of clocks as close as possible

4
NTP Symmetric mode

• There can be a non-negligible delay between the
  arrival of one message and the dispatch of the
  next
• Delay total transmission time of the two
  messages
• di (Ti Ti-3 ) (Ti-1 Ti-2)
• Offset of clock A relative to clock B
• Offset of clock A oi ((Ti-2 Ti-3 ) ( Ti-1
  Ti))/2
• Accuracy bound di /2

5
Logical Clock Synchronization

• Event ordering happened before (?), concurrent
  ()
• Lamports algorithm single timestamp clock
  synchronization features
• If a ? b then V(a) lt V(b)
• The reverse is not always true
• Timestamp vector synchronization and features
• a ? b iff V(a) lt V(b)
• a b iff neither V(a) V(b) nor V(b) V(a)
• Application of timestamp vectors causal ordered
  multicast

6
Interprocess Communication (IPC)

• Socket operations and Socket types
• socket
• bind
• listen, accept, connect
• read/write, send/recv, sendto/recvfrom,
  sendmsg/recvmsg
• close/shutdown
• Programming by using sockets

7
Remote Procedure Call (RPC)

• Interface Definition of a client-server system
  (Sun XDR)
• Client program development
• Server program development
• Client-server binding in RPC

8
Internetworking

• IP addressing
• classful addressing rational, drawback
• Classless InterDomain Routing (CIDR)
• Address allocation and notation
• Routing in CIDR
• NAT (Network Address Translation)
• Internal addrs inside an org and external addrs
  for Internet
• Address translation
• DHCP (Dynamic Host Configuration Protocol)
• Dynamic allocation of IP addresses
• DHCP server and DHCP relay-agent for address
  allocation

9
Naming Services

• Domain Name System (DNS) architecture
• DNS host name resolution / IP address resolution
• Client/server node configuration in DNS
• Administration operations on DNS

10
UNIX File Systems

• Directory structure
• File inode structure
• File access structure (file descriptor, file
  table and incore-inode table)
• File operations, open/read/close

11
Distributed File Systems

• Distributed file systems vs. Centralized file
  systems (flat file server, stateless, idempotent,
  etc.)
• Flat file service and Directory service
• Client module (application user interface) and
  emulation of traditional file systems
• implementation of UNIX FS interface as library
  routines
• SUN Network File System (NFS)
• Mount/remote mount operations to construct a
  global file hierarchy
• Implementation of the NFS (virtual file layer)

12
Transaction processing systems

• Definition of atomic transactions
• Atomicity and serializability
• Interleaving of concurrent transactions
• Failure recovery of transactions (Atomicity)
• Tentative phase and commit phase
• Intention list method
• Shadow version method

13
Transaction processing systems (contd)

• Concurrency control of transactions
  (Serializability)
• 2Phase locking
• Lock the data before access and hold the lock
• read-lock / write-lock
• Serializability order
• Advantages / disadvantages
• Timestamp ordering
• Transactions are serialized in the order of their
  starting time
• Transaction timestamp, read-timestamp /
  write-timestamp of data
• Advantages / disadvantages
• Optimistic method
• Transactions are serialized in the order of their
  close time
• Transactions always proceed in tentative phase
  and check conflicts when they close
• Advantages / disadvantages

14
Web Searching

• Structure of web searching
• Spider operations (HTTP protocol)
• Web digraph
• Back links and backlink applications
• Page ranking
• Building inverted file for searching