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Arpit Bhayani Blogs

001 Ai Topological Sort

119-consistency

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Decoding Consistency - The C in ACID

Source: https://arpitbhayani.me/blogs/consistency Date: 2021-07-02

Understand database consistency (the "C" in ACID) and its importance. Learn how databases maintain data correctness through rules and constraints.

In this short essay, we dive deep and understand the “C” in ACID - Consistency.

In this quick read, we will take a detailed look into Consistency, understand its importance, functioning, and how the database implements it.

What is Consistency?

In the context of databases, Consistency is Correctness, which means that under no circumstance will the data lose its correctness.

001-ai-topological-sort.md

002 Temporal Primer

002-temporal-primer.md

003 Rag Production

003-rag-production.md

004 Structure Of Llm Chat

004-structure-of-llm-chat.md

005 How Llms Work

005-how-llms-work.md

006 Monolith Is Distributed System

006-monolith-is-distributed-system.md

007 Defensive Databases

007-defensive-databases.md

008 Bm25

009 Join Algorithms

009-join-algorithms.md

010 Venting At Work

010-venting-at-work.md

011 Half Life

011-half-life.md

012 Multi Paxos

012-multi-paxos.md

013 Mysql Replication Internals

013-mysql-replication-internals.md

014 Bloom Filters

014-bloom-filters.md

015 Clock Sync Nightmare

015-clock-sync-nightmare.md

016 Kafka Partitions

016-kafka-partitions.md

017 Product Quantization

017-product-quantization.md

018 Qkv Matrices

018-qkv-matrices.md

019 Deleted Production

019-deleted-production.md

020 How Llm Inference Works

020-how-llm-inference-works.md

021 Blocking Queues

021-blocking-queues.md

022 Heartbeats In Distributed Systems

022-heartbeats-in-distributed-systems.md

023 Cassandra Writes

023-cassandra-writes.md

024 Redis Replication

024-redis-replication.md

025 Arrogant People At Work

025-arrogant-people-at-work.md

026 Cdn Content Replication

026-cdn-content-replication.md

027 Cant Fix Everything Day One

027-cant-fix-everything-day-one.md

028 Emotions At Work

028-emotions-at-work.md

029 Grpc Http2

029-grpc-http2.md

030 Meetings With No Agenda Are A Waste Of Time

030-meetings-with-no-agenda-are-a-waste-of-time.md

031 Growth Is Not About Doing Everything

031-growth-is-not-about-doing-everything.md

032 Career Longevity Vs Job Hopping

032-career-longevity-vs-job-hopping.md

033 Stay Relevant At Higher Salary Levels

033-stay-relevant-at-higher-salary-levels.md

034 Why Consensus

034-why-consensus.md

035 Database Deadlocks

035-database-deadlocks.md

036 Cpu Cache Locality

036-cpu-cache-locality.md

037 Eventual Consistency

037-eventual-consistency.md

038 Dns Udp Tcp

038-dns-udp-tcp.md

039 Masters

040 Empathy Makes Great Engineers Unstoppable

040-empathy-makes-great-engineers-unstoppable.md

041 Good Mentors Build People

041-good-mentors-build-people.md

042 Always Have Back Burner Projects

042-always-have-back-burner-projects.md

043 Before You Push Back Know What Youre Standing On

043-before-you-push-back-know-what-youre-standing-on.md

044 Be The One They Can Count On

044-be-the-one-they-can-count-on.md

045 How Much People Bet On You

045-how-much-people-bet-on-you.md

046 How To Get Leadership To Say Yes To Your Project

046-how-to-get-leadership-to-say-yes-to-your-project.md

047 Dont Let Your Best Ideas Die In Silence

047-dont-let-your-best-ideas-die-in-silence.md

048 Be Someone Others Want To Work With

048-be-someone-others-want-to-work-with.md

049 Dont Fall For Xy Problem Ask Right Questions

049-dont-fall-for-xy-problem-ask-right-questions.md

050 Biggest Lie Startups Tell Engineers

050-biggest-lie-startups-tell-engineers.md

051 Promotions Are Proactive Not Reactive

051-promotions-are-proactive-not-reactive.md

052 Not Enough To Be Right Learn To Be Heard

052-not-enough-to-be-right-learn-to-be-heard.md

053 No One Ships Alone

053-no-one-ships-alone.md

054 Not Every Mistake Needs A Correction

054-not-every-mistake-needs-a-correction.md

055 Build Influence At Work

055-build-influence-at-work.md

056 Your Soft Skills Arent Soft At All

056-your-soft-skills-arent-soft-at-all.md

057 Experience Before Forming Opinion

057-experience-before-forming-opinion.md

058 Curiosity And High Bias For Action

058-curiosity-and-high-bias-for-action.md

059 Worklog

060 Mistakes And Growth

060-mistakes-and-growth.md

061 Own It Instead Of Sweeping It Aside

061-own-it-instead-of-sweeping-it-aside.md

062 Dont Wait Step Up

062-dont-wait-step-up.md

063 Temporary Fix Is Permanent

063-temporary-fix-is-permanent.md

064 Interview Bias And What Sets You Apart

064-interview-bias-and-what-sets-you-apart.md

065 Saying This Isnt My Problem Is A Problem

065-saying-this-isnt-my-problem-is-a-problem.md

066 Okr

067 Miscommunication

067-miscommunication.md

068 When In Doubt Code It Out

068-when-in-doubt-code-it-out.md

069 Follow Up Without Annoying People

069-follow-up-without-annoying-people.md

070 Lead Projects That Land

070-lead-projects-that-land.md

071 Abstract Thinking Skill Next Decade

071-abstract-thinking-skill-next-decade.md

072 We Engineers Suck At Task Estimation

072-we-engineers-suck-at-task-estimation.md

073 Shiny Object Syndrome In Tech

073-shiny-object-syndrome-in-tech.md

074 3p

075 Leverage The Equilibrium

075-leverage-the-equilibrium.md

076 On Demand Container Loading In Aws Lambda

076-on-demand-container-loading-in-aws-lambda.md

077 Sql Has Problems We Can Fix Them Pipe Syntax In Sql

077-sql-has-problems-we-can-fix-them-pipe-syntax-in-sql.md

078 Nanolog A Nanosecond Scale Logging System

078-nanolog-a-nanosecond-scale-logging-system.md

079 Best Resource Is Mythical

079-best-resource-is-mythical.md

080 Wtf The Who To Follow Service At Twitter

080-wtf-the-who-to-follow-service-at-twitter.md

081 Know A Lot

081-know-a-lot.md

082 Out Of Syllabus

082-out-of-syllabus.md

083 Negotiate The Offer

083-negotiate-the-offer.md

084 Never Bad Mouth Your Ex Exployer

084-never-bad-mouth-your-ex-exployer.md

085 Culture Fit

085-culture-fit.md

086 Quantification In Resume

086-quantification-in-resume.md

087 Hiring Is Unfair

087-hiring-is-unfair.md

088 Questions For Interviewers

088-questions-for-interviewers.md

089 Collaboration Communication

089-collaboration-communication.md

090 Out Of Vicious Interview Cycle

090-out-of-vicious-interview-cycle.md

091 Pitch Projects Not Ideas

091-pitch-projects-not-ideas.md

092 Read Design Docs

092-read-design-docs.md

093 Read Rca Docs

093-read-rca-docs.md

094 Start Generalist

094-start-generalist.md

095 Do Not Rely On Summaries

095-do-not-rely-on-summaries.md

096 Structure Your Design Interviews

096-structure-your-design-interviews.md

097 Title Inflation

097-title-inflation.md

098 Find Your Own Project

098-find-your-own-project.md

099 Six Pointers To Crack Coding And Design Interviews

099-six-pointers-to-crack-coding-and-design-interviews.md

100 Keep Yourself Unblocked

100-keep-yourself-unblocked.md

101 Genetic Knapsack

101-genetic-knapsack.md

102 Pseudorandom Number Generation Lfsr

102-pseudorandom-number-generation-lfsr.md

103 How Indexes Work On Partitioned And Sharded Data

103-how-indexes-work-on-partitioned-and-sharded-data.md

104 Some Data Partitioning Strategies For Distributed Data Stores

104-some-data-partitioning-strategies-for-distributed-data-stores.md

105 Data Partitioning

105-data-partitioning.md

106 Leaderless Replication

106-leaderless-replication.md

107 Conflict Resolution

107-conflict-resolution.md

108 Conflict Detection

108-conflict-detection.md

109 Multi Master Replication

109-multi-master-replication.md

110 Monotonic Reads

110-monotonic-reads.md

111 Read Your Write Consistency

111-read-your-write-consistency.md

112 Handling Outages Master Replica

112-handling-outages-master-replica.md

113 Replication Formats

113-replication-formats.md

114 Replication Strategies

114-replication-strategies.md

115 Master Replica Replication

115-master-replica-replication.md

116 Durability

116-durability.md

117 Isolation

117-isolation.md

118 Atomicity

118-atomicity.md

119 Consistency

119-consistency.md

120 Architectures In Distributed Systems

120-architectures-in-distributed-systems.md

121 Mistaken Beliefs Of Distributed Systems

121-mistaken-beliefs-of-distributed-systems.md

122 Fork Bomb

122-fork-bomb.md

123 Chained Operators Python

123-chained-operators-python.md

124 Taxonomy On Sql

124-taxonomy-on-sql.md

125 The Weird Walrus

125-the-weird-walrus.md

126 Fully Persistent Arrays

126-fully-persistent-arrays.md

127 Persistent Data Structures Introduction

127-persistent-data-structures-introduction.md

128 Constant Folding Python

128-constant-folding-python.md

129 String Interning Python

129-string-interning-python.md

130 Recursion Visualizer Python

130-recursion-visualizer-python.md

131 Flajolet Martin

131-flajolet-martin.md

132 2q Cache

132-2q-cache.md

133 Israeli Queues

133-israeli-queues.md

134 1d Terrain

134-1d-terrain.md

135 Jaccard Minhash

135-jaccard-minhash.md

136 Ts Smoothing

136-ts-smoothing.md

137 Lfu

138 Morris Counter

138-morris-counter.md

139 Slowsort

139-slowsort.md

140 Bitcask

141 Phi Accrual

141-phi-accrual.md

142 10x Engineer

142-10x-engineer.md

143 Decipher Repeated Key Xor

143-decipher-repeated-key-xor.md

144 Decipher Single Xor

144-decipher-single-xor.md

145 Python Iterable Integers

145-python-iterable-integers.md

146 Inheritance C

146-inheritance-c.md

147 Rum

148 Consistent Hashing

148-consistent-hashing.md

149 Python Caches Integers

149-python-caches-integers.md

150 Fractional Cascading

150-fractional-cascading.md

151 Copy On Write

151-copy-on-write.md

152 Midpoint Insertion Caching Strategy

152-midpoint-insertion-caching-strategy.md

153 Fsm Python

153-fsm-python.md

154 Bayesian Average

154-bayesian-average.md

155 Sliding Window Ratelimiter

155-sliding-window-ratelimiter.md

156 Idf

157 Better Programmer

157-better-programmer.md

158 Python Prompts

158-python-prompts.md

159 Rule 30 Cellular Automata

159-rule-30-cellular-automata.md

160 Function Overloading

160-function-overloading.md

161 Isolation Forest

161-isolation-forest.md

162 Image Steganography

162-image-steganography.md

163 Long Integers Python

163-long-integers-python.md

164 I Changed My Python

164-i-changed-my-python.md

165 Benchmark And Compare Pagination Approach In Mongodb

165-benchmark-and-compare-pagination-approach-in-mongodb.md

166 Mongodb Cursor Skip Is Slow

166-mongodb-cursor-skip-is-slow.md

167 Fast And Efficient Pagination In Mongodb

167-fast-and-efficient-pagination-in-mongodb.md

168 Making Http Requests Using Netcat

168-making-http-requests-using-netcat.md

Database systems allow us to define rules that the data residing in our database are mandated to adhere to. Few handy rules could be

balance of an account should never be negative
no orphan mapping: there should not be any mapping of a person whose entry from the database is deleted.
no orphan comment: there should not be any comment in the database that does not belong to an existing blog.

These rules can be defined on a database using Constraints, Cascades, and Triggers; for example, Foreign Key constraints, Check constraints, On Delete Cascades, On Update Cascades, etc.

Consistency ACID Database

Role of the database engine in ensuring Consistency

An ACID-compliant database engine has to ensure that the data residing in the database continues to adhere to all the configured rules. Thus, even while executing thousands of concurrent transactions, the database always moves from one consistent state to another.

What happens when the database discovers a violation?

Database Engine rollbacks the changes, which ensures that the database is reverted to a previous consistent state.

What happens when the database does not find any violation?

Database Engine will continue to apply the changes, and once the transaction is marked successful, this state of the database becomes the newer consistent state.

Why is consistency important?

The answer is very relatable. Would you ever want your account to have a negative balance? No. This is thus defined as a rule that the database engine would have to enforce while applying any change to the data.

How does the database ensure Consistency?

Integrity constraints are checked when the changes are being applied to the data.

Cascade operations are performed synchronously along with the transaction. This means that the transaction is not complete until the primary set of queries, along with all the eligible cascades, are applied. Most database engines also provide a way to make them asynchronous, allowing us to keep our transactions leaner.

✨ Next up is “I” in ACID - Isolation. Stay tuned.

References

ACID - Wikipedia
Consistency
Foreign Key Constraints
ACID Explained - BMC
ACID properties of transactions
ACID Compliance: What It Means and Why You Should Care