What
is Concurrency Control
Process of managing simultaneous execution of
transactions in a shared database, to ensure the serializability of
transactions, is known as concurrency control.
Why
we need Concurrency Control
Simultaneous execution of transactions over a shared
database can create several data integrity and consistency problems:
1. Lost
Updates.
2. Uncommitted
Data.
3. Inconsistent
retrievals
.
Concurrency
Control Techniques
• Pessimistic concurrency control
• Optimistic concurrency control
Pessimistic
Concurrency Control
•
Pessimistic Concurrency Control assumes
that conflicts will happen
•
Pessimistic Concurrency Control
techniques detect conflicts as soon as they occur and resolve them using
blocking.
Optimistic
Concurrency Control
•
Optimistic Concurrency Control assumes
that conflicts between transactions are rare.
•
Does not require locking
•
Transaction executed without
restrictions
•
Check for conflicts just before commit
Description:-
Concurrency control theory has two
classifications for the methods of instituting concurrency control:
Pessimistic concurrency control:-
in pressimistic concurrency control user can locked the data when user is
readit.
Optimistic concurrency control:-
in pressimistic concurrency control user can locked the data when user is
readit.
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