--- title: Need to migrate from one database to another without... description: Dual writes are a database migration technique where every write operation is sent to both the old and new databases simultaneously, keeping them synchronized... canonical: https://daily.dev/posts/need-to-migrate-from-one-database-to-another-without-downtime--bm28anadf twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Need to migrate from one database to another without downtime? | daily.dev og:description: Dual writes are a database migration technique where every write operation is sent to both the old and new databases simultaneously, keeping them synchronized... og:url: https://daily.dev/posts/need-to-migrate-from-one-database-to-another-without-downtime--bm28anadf og:image: https://api.daily.dev/og/posts/bm28anaDf.png og:image:alt: Need to migrate from one database to another without downtime? og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Need to migrate from one database to another without downtime? **[ITNEXT](https://daily.dev/sources/itnext)** · 3 min read · 1 upvotes · 0 comments ## Summary Dual writes are a database migration technique where every write operation is sent to both the old and new databases simultaneously, keeping them synchronized while both remain active. This enables gradual traffic migration without downtime. The main challenge is handling partial failures — when one database succeeds and the other fails — requiring retry logic, rollback mechanisms, or reconciliation processes. Dual writes work best when eventual consistency is acceptable and reconciliation processes exist, but become complex in systems requiring strict consistency guarantees. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### What are dual writes in the context of database migration? Dual writes mean every write operation (insert, update, delete) is sent to both the old and new database simultaneously, keeping them synchronized while both remain active. This lets traffic be gradually migrated to the new database without a large downtime window. It is commonly implemented in the application layer by maintaining two database connection pools, though infrastructure tools like Envoy can mirror requests for certain technologies such as Redis. _daily.dev surfaces migration strategy discussions for engineers weighing dual writes against other zero-downtime approaches._ ### What is the hardest part of implementing dual writes for database migration? The hardest part is handling partial failures, not the act of writing twice. When a write succeeds on one database but fails on the other, the two systems disagree, raising questions about whether the operation can be safely retried, whether the successful write can be rolled back, and whether locking or reconciliation mechanisms exist to resolve the drift. _Engineers debugging consistency issues during migrations often track patterns like this on daily.dev._ ### When does the dual writes migration pattern work best? Dual writes work best when updates occur frequently, eventual consistency is acceptable, reconciliation processes already exist, and future updates naturally correct any drift between the two databases. They become much harder to justify in systems that require strict consistency guarantees for every single operation. _Teams deciding between migration strategies can follow tradeoff analyses like this on daily.dev._ ## Similar posts on daily.dev - [Zero Downtime Multicloud Migrations for Observability Control Planes](https://daily.dev/posts/zero-downtime-multicloud-migrations-for-observability-control-planes-pjd0wxp7j) · DevOps.com · 0 upvotes · 0 comments - [Dual-Read Cache Consistency in Monolith DB Migrations](https://daily.dev/posts/dual-read-cache-consistency-in-monolith-db-migrations-yoqhsvloq) · SitePoint · 3 upvotes · 0 comments - [How to Fix the Dual-Write Problem in Node.js with the Outbox Pattern](https://daily.dev/posts/how-to-fix-the-dual-write-problem-in-node-js-with-the-outbox-pattern-kobnx54pc) · freeCodeCamp · 1 upvotes · 0 comments - [You Wrote To Two Databases. Did Both Succeed?](https://daily.dev/posts/you-wrote-to-two-databases-did-both-succeed--1vbubwl2g) · ITNEXT · 0 upvotes · 0 comments - [Cloud Bits: Breaking the Double Write – A Guide to Distributed Data Consistency – Distributed Computing Musings](https://daily.dev/posts/cloud-bits-breaking-the-double-write-a-guide-to-distributed-data-consistency-distributed-comput-i2embckph) · Distributed Computing Musings · 0 upvotes · 0 comments --- Tags: [#database](https://daily.dev/tags/database), [#distributed-systems](https://daily.dev/tags/distributed-systems) [View this post on daily.dev](https://daily.dev/posts/need-to-migrate-from-one-database-to-another-without-downtime--bm28anadf) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Need to migrate from one database to another without downtime?","url":"https://daily.dev/posts/need-to-migrate-from-one-database-to-another-without-downtime--bm28anadf","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/need-to-migrate-from-one-database-to-another-without-downtime--bm28anadf"},"datePublished":"2026-07-13T17:35:51.845Z","dateModified":"2026-09-13T19:39:17.544Z","description":"Dual writes are a database migration technique where every write operation is sent to both the old and new databases simultaneously, keeping them synchronized...","image":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/e34678ecfbb3933301afa4fadeff5843?_a=AQAEuop","thumbnailUrl":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/e34678ecfbb3933301afa4fadeff5843?_a=AQAEuop","isAccessibleForFree":true,"articleSection":"ITNEXT","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"ITNEXT","logo":"https://media.daily.dev/image/upload/t_logo,f_auto/v1/logos/itnext2","url":"https://daily.dev/sources/itnext"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/need-to-migrate-from-one-database-to-another-without-downtime--bm28anadf","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":1},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"database,distributed-systems","timeRequired":"PT3M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"ITNEXT","item":"https://daily.dev/sources/itnext"},{"@type":"ListItem","position":3,"name":"Need to migrate from one database to another without downtime?"}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/need-to-migrate-from-one-database-to-another-without-downtime--bm28anadf#faq","mainEntity":[{"@type":"Question","name":"What are dual writes in the context of database migration?","acceptedAnswer":{"@type":"Answer","text":"Dual writes mean every write operation (insert, update, delete) is sent to both the old and new database simultaneously, keeping them synchronized while both remain active. This lets traffic be gradually migrated to the new database without a large downtime window. It is commonly implemented in the application layer by maintaining two database connection pools, though infrastructure tools like Envoy can mirror requests for certain technologies such as Redis. daily.dev surfaces migration strategy discussions for engineers weighing dual writes against other zero-downtime approaches."}},{"@type":"Question","name":"What is the hardest part of implementing dual writes for database migration?","acceptedAnswer":{"@type":"Answer","text":"The hardest part is handling partial failures, not the act of writing twice. When a write succeeds on one database but fails on the other, the two systems disagree, raising questions about whether the operation can be safely retried, whether the successful write can be rolled back, and whether locking or reconciliation mechanisms exist to resolve the drift. Engineers debugging consistency issues during migrations often track patterns like this on daily.dev."}},{"@type":"Question","name":"When does the dual writes migration pattern work best?","acceptedAnswer":{"@type":"Answer","text":"Dual writes work best when updates occur frequently, eventual consistency is acceptable, reconciliation processes already exist, and future updates naturally correct any drift between the two databases. They become much harder to justify in systems that require strict consistency guarantees for every single operation. Teams deciding between migration strategies can follow tradeoff analyses like this on daily.dev."}}]} ```