Crisp Reading Notes on Latest Technology Trends and Basics

Isolation Levels

This write-up will contain notes from the following reference.

http://www.cs.umb.edu/~poneil/iso.pdf

According to the reference, there are six types of isolation provided by Database Providers.

Two of these – Cursor Stability and Snapshot Isolation are variants of the four ANSI standards, because of ambiguity in the ANSI standards.

The paper also tries to map Execution History in terms of “Multi Version Concurrency Control”, which is a new concept.

Situation implemented Situation to avoid History to avoid Locks Required Avoided with Locks
Read Committed Read Uncommitted W1(x),R2(x), { C1 or C2 } Write Lock till Commit W1(x),R2(x),{ C1 or A1 or C2 or A2 }
Repeatable Read Write after Read R2(x),W1(x), C1, R2(x), { C1 or C2 } Read lock till Commit R2(x),W1(x),
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