CS Notes Archives - Coddicted

Durability in Databases

Jan

30

2022

Durability is the process of persisting the writes that clients make to the database to a non-volatile storage disk. Caveat is that the writes should also be committed. This means once the commit has succeeded and right after that our system loses power or the system crashes and we need to restart, then our changes ...

Transaction Isolation

Jan

17

2022

The third of ACID properties “Isolation” is basically the question: “Can an in-progress transaction see changes made by another transaction running in-parallel?” Follow up to it would be “If yes, at what point of time can it see such changes?” Let’s try to analyse some aspects of the above question(s) from the db system implementation ...

Consistency in Databases

Jan

9

2022

It is one of the ACID properties which is often traded-off between different database systems (relational/ nosql/ graph etc.) (heard of eventually consistent DB?). It is often sacrificed for speed, scalability in some databases It can be categorised in two parts: Consistency in DataConsistency in Read Data Consistency That a transaction leaves the updated database ...

Atomicity

Dec

27

2021

Atomicity is one of the four ACID properties that define a database system. While ACID properties are usually referenced in Relational DBMS, they are still an applicable concept for nearly any database system out there. Let’s see what it is… All queries in a transaction must succeed. Like an atom (something which can’t be split)If ...

Database Transaction

Dec

22

2021

In this article we discuss about what is a Database Transaction, what are its intricacies and why it’s needed? A transaction is simply “a collection of SQL queries which are treated as a single unit of work.“ What is the need of a db transaction? Let’s think about the scenario where transactions were not possible, ...

Lossless Dependency Preserving 3NF decomposition Algorithm 2

Dec

25

2014

The minimal cover of F is given 1. Search for dependencies in F-having the same attribute set on the left hand side A: A->B1, A->B2, A->B3, …, A->Bk And construct relation as (A, B1, B2, B3,…, Bk) 2. Construct a relation with remainder attributes. 3. In case none of the relations has a candidate key, ...

Recommended books for GATE (Computer Science)

May

23

2013

Socratic Touch…

Apr

18

2013

Who is Socrates? Socrates ( 469 BC – 399 BC) was a classical Greek Athenian philosopher. Credited as one of thefounders of Western philosophy, he is an enigmatic figure known chiefly through the accounts of later classical writers, especially the writings of his students Plato and Xenophon, and the plays of his contemporary Aristophanes. ...

Wait-die and Wound-wait Schemes 11

Apr

18

2013

Wait-die scheme: It is a non-preemptive technique for deadlock prevention. When transaction Ti requests a data item currently held by Tj, Ti is allowed to wait only if it has a timestamp smaller than that of Tj (That is Ti is older than Tj), otherwise Ti is rolled back (dies) For example: Suppose that transaction T22, T23, T24 have time-stamps 5, 10 and ...

Validation Based Protocol

Apr

18

2013

It imposes less overhead Also based on Timestamp Protocol. It has three phases: Read Phase: During this phase, the system executes transaction Ti. . It reads the values of the various data items and stores them in variable local to Ti. It performs all the write operations on temporary local variables without update of the actual database. ...