Download Concurrency Control

CONCURENCY CONTROL
DISTRIBUTED DATABASE
MAIN TOPICS

Transaction managements
Centralized database
 Distributed database


Consistency control
Centralized database
 Distributed database

DATABASE CONSISTENCY
Setiap data yang disimpan ke dalam database
harus konsisten
 Dikatakan konsisten jika data yang dimasukkan
ke dalam database, sesuai dengan kriteria
 Misal:

SSN (social security number harus mempunyai nilai
unik)
 Umur harus mempunyai nilai positif
 Employee harus bekerja pada satu departemen
 Saldo dalam rekening harus mempunyai nilai positif

TRANSACTION
Transaksi
merupakan
kumpulan dari
operasi yang
dilakukan pada
sebuah data
 Suatu transaksi
harus mempunyai
sifat ACID
(Atomicity,
Consistency,
Isolation, Durability)

TRANSACTION (CONT’D)



Suatu transaksi di dalam database yang utama adalah
proses Read dan Write
Setiap transaksi berisi sekumpulan operasi yang terurut
Pada multi-user transaction processing terdapat banyak
transaksi yang dijalankan dalam sekali waktu, dan bisa
jadi operasi-operasi yang dilakukan saling tumpang tindih
ACID
Atomicity – all of the operation of transaction are
carried out or none of them are carried out.
 Consistency – property of transaction requires a
transaction to be written correctly
 Isolation – property of transaction requires that
transaction to be run out without interference
from other transaction – can be achieve by
locking or timestamping
 Durability – property of a transaction requires
the value that the transaction commit to the
database persistent.

TRANSACTION LIFE CYCLE
MULTITRANSACTION PROCESSING SYSTEM
Schedule
 Conflict
 Equivalence
 Serializable Schedule

SCHEDULING
Schedule is a the total order of operations or set
of transactions.
 Scheduling type

Serial Schedule – the operations for each transaction
do not overlap in time
 Parallel Schedule – the operations for each
transaction do overlap in time

SERIAL AND PARALLEL SCHEDULE
SERIES TRANSACTION

Two or more transactions running in series
maintain the consistency of database
CONFLICTS

Conflicts occurs when two running transactions
perform noncompatible operations on the same
data item of the database
CONFLICTS (CONT’D)

Each of that schedule produce some anomalies



Unrepeatable read anomaly (in-S1)
Reading uncommitted data / dirty read anomaly (in
S2)
Overwriting uncommitted data anomaly (in S2)
EQUIVALENCE

The problems


Concurrent transactions can cause anomaly – the
anomaly can destroy consistency of database
Solution
Run all transaction in series
 Run transaction concurrently


Goal


Preserve the consistency of database
If the 2nd solution can achieve the goal –
Equivalence
EQUIVALENCE TRANSACTION

Example:
SERIALIZABLE SCHEDULE
A schedule is said to be serializable if it
equivalent to serrial schedule
 The check for serial schedule equivalence serializability.


The T1 transaction (R1, W1) must be committed,
before T2 transaction (R2, W2) being executed
SERIALIZABLE
EXAMPLE
SERIALIZABLE
EXAMPLE