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2 posts tagged with "Databases"

Database systems

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MVCC Visibility Rules

· One min read
Abhishek Tripathi
Abhishek Tripathi
Curiosity brings awareness.

MVCC Visibility Rules Demonstration

Illustrates how transactions see data based on snapshot isolation. Focus on T3's reads and how its snapshot (taken at t=40) affects what it sees from T1 and T2, even after they commit.

Step: 0/14 | Time: 0
Next TxID: 1 | Committed: [0]

Data Item Versions (Global State)

Current Operation

None

Transaction States & Snapshots

No active transactions.

Transaction Timelines

0
10
20
30
40
50
60
70

T1

B
R
W
R
C

T2

B
R
W
R
C

T3

B
R
R
C

Legend

B
Begin
R
Read
W
Write
C
Commit
A
Abort

Database Isolation (dirty reads)

· 3 min read
Abhishek Tripathi
Abhishek Tripathi
Curiosity brings awareness.

Understanding Dirty Reads: A Database Isolation Problem​

What is a Dirty Read?​

A dirty read occurs when a transaction reads data that has been written by another transaction but not yet committed. If the writing transaction rolls back, the data read by the first transaction becomes invalid—hence, "dirty."

This can lead to inconsistent or incorrect results in applications, especially in systems where multiple users or processes are accessing and modifying the data concurrently.