CONCURRENCY CONTROL

Problem Definition
1. Objective
  1. Maximize transaction throughput(work perform) while preventing interference among multiple users
  2. Throughput: number of transactions processed per unit time eg >1million transaction per second
2. Constraint
  1. No interference: result same as serial/sequential effect
  2. Interference occurs on commonly manipulated data known as hot spots
Concurrency Control Problem
1. Lost Update Problem e.g:slide no.11&12
  1. Preventing Lost Update Problem Using 2PL e.g:slide no.28
2. Uncommitted Dependency Problem e.g:slide no.13&14
  1. Preventing Uncommitted Using 2PL e.g:slide no.29
Concurrency Control Tools
1. Locking
  1. Obtain lock before accessing an item
  2. Wait if a conflicting lock is held
    1. Shared lock (S lock): conflicts with exclusive locks
    2. Exclusive lock (X lock): conflicts with all other kinds of locks
  3. Locking Conflict e.g:slide no.22
  4. Locking Granularity e.g:slide no 23
2. Deadlock
  1. Deadlock(Mutual Waiting) e.g:slide no.24
  2. Deadlock Resolution
    1. Detection
      1. Overhead is reasonable for deadlocks among 2 or 3 transactions
    2. Timeout
      1. Waiting limit
      2. Can abort transactions that are not deadlocked
      3. Timeout interval is difficult to determine

Resource summary

	Created by azzaiqmal about 10 years ago