SQL Server - Bài 10

Managing Transaction and
Lock
Vu Tuyet Trinh

Hanoi University of Technology
1
MicrosoftMicrosoft
Transaction

A sequence of tasks that together constitute a logical unit
of work

Ensuring the highest level of integrity and consistency
within a database

Used when statements are processed
MicrosoftMicrosoft
ACID Properties

Atomicity

All or none

Consistency

Leave data in a consistent state

Isolation

Don’t show data that’s ½ done


Durability

Modifications are permanent
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Overview
√
Transaction

Review of Transaction Log

Introduction to Transactions and Locks

Managing Transactions

SQL Server Locking & Managing Locks
MicrosoftMicrosoft
Transaction Log Architecture

Write-Ahead transaction log

Flushing the page and dirty Pages

Use of checkpoints

Minimize what must be processed to recover

Truncating the transaction log

Shrinking the transaction log


DBCC SHRINKDATABASE

DBCC SHRINKFILE
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Transaction Recovery and Checkpoints
Transaction Recovery Action Required
None
Checkpoint System Failure
1
1
2
2
3
3
4
4
5
5
Roll forward
Roll back
Roll forward
Roll back
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Concurrency Control

Pessimistic concurrency control

High contention for data

Optimistic concurrency control


Low contention for data
MicrosoftMicrosoft
Lockable Resources


Item
Item


Description
Description
RID Row identifier
Key Row lock within an index
Page
Extent
Table
Data page or index page
Group of pages
Entire table
Database Entire database
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Types of Locks

Basic locks

Shared (LS)

Exclusive (LX)


Special situation locks

Intent

Update

Schema

Bulk update
MicrosoftMicrosoft
Lock Compatibility

Locks may or may not be compatible with other Locks

Examples

Shared locks are compatible with all locks except exclusive

Exclusive locks are not compatible with any other locks

Update locks are compatible only with shared locks
falsefalseLX
falsetrueLS
LXLS