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126 questions, 454 terms and 400 topics in 20 areas.
50 results for “Database Migration”
Airbnb's Service-Oriented Migration
Airbnb decomposed a large Rails monolith by first extracting a unified data-access layer, so that services were built on owned data rather than on shared database tables.
Zero-Downtime Migration
Changing a schema or system while it stays in service, by adding the new alongside the old, migrating, then removing the old.
Blue-Green Database Schema
The constraint that makes fast rollback actually work — both application versions must be able to run against one schema at the same time.
Database Index
A secondary structure that lets the engine find rows without scanning, trading write cost and storage for read speed.
Database per Service
Each service owning its own datastore, with no other service reading or writing it directly.
Graph Database
A store whose first-class citizens are nodes and the relationships between them, making multi-hop traversal cheap.
Migration Wave
A batch of applications migrated together, sequenced so that dependencies move in a workable order and each wave delivers learning for the next.
Six Rs of Migration
The standard menu of options for each application in a migration — rehost, replatform, refactor, repurchase, retire, retain.
Slack's Cellular Migration
After repeated availability-zone-level incidents, Slack rebuilt its infrastructure into per-zone cells with the ability to drain traffic away from a failing zone in minutes.
Vector Database
A store optimised for approximate nearest-neighbour search over high-dimensional embeddings.
Application Discovery
Establishing what applications exist, what they depend on, who owns them and whether anyone uses them — the step whose absence makes every later step a guess.
CDC Initial Snapshot
The consistent full copy taken when a CDC pipeline starts, before streaming begins — and the step that determines whether the target is correct.
Capital One's Data Centre Exit
A major US bank closed all eight of its data centres and moved fully to public cloud, treating governance automation as the enabling technology rather than a constraint.
Change Data Capture
Publishing a stream of a database's row-level changes by reading its replication log, without modifying the application that owns it.
Connection Pool
A fixed set of reusable database connections shared by an application's requests, and one of the most common hidden capacity ceilings.
Connection Proxy
A pooling layer between applications and a managed database that multiplexes many client connections onto a small number of database connections.
Dual Write
Writing the same change to both the old and new stores during a migration, and the reconciliation that makes it trustworthy.
Foreign Key Constraint
A database-enforced rule that a referencing value must exist in the referenced table — referential integrity that no application bug can violate.
Hexagonal Architecture
Putting the domain at the centre and letting everything external — UI, database, queues — attach through ports implemented by replaceable adapters.
Join Strategies
The three ways a database combines two row sets — nested loop, hash join and merge join — and the conditions under which each is correct.
Log-Based CDC
Capturing changes by reading the database's own write-ahead log, which sees every change with no load on the source and no application involvement.
Parallel Run
Running the old and new systems side by side on the same inputs and comparing outputs, before the new one is trusted.
Point-in-Time Recovery
Restoring a database to any moment within a retention window by replaying transaction logs onto a base backup, rather than only to a snapshot boundary.
Provisioned vs Serverless Capacity
Paying for a fixed database size continuously, versus paying for capacity consumed with automatic scaling — a crossover decision driven by duty cycle.
Query Plan
The database's chosen strategy for executing a query, and the first thing to look at when one is slow.
Read Replica
A copy of a database that receives changes from the primary and serves read-only queries, spreading read load.
Replatform
Migrating an application largely as-is while making targeted changes to exploit the target platform — usually the best return per unit of effort.
Service Registry
The database of currently available service instances and their addresses, maintained by registration and pruned by health checking.
Strangler Facade
The routing layer in front of a legacy system that decides, per capability, whether a request goes to the old implementation or the new one.
Strangler Fig
Replacing a legacy system incrementally by routing individual capabilities to new implementations behind a facade, until nothing routes to the old system.
An estate has database passwords in environment variables across 200 services. Design the migration to a secrets manager.
Sequence it by risk, not by convenience Phase 0 — stop the bleeding. Secret scanning in CI and on the existing repositories, blocking new commits containing cre
A downstream team needs to react to order changes. The order service can publish events, or they can consume CDC from its database. Which, and why?
The recommendation: published events, with CDC as the mechanism if needed The distinction that matters is what the consumer becomes coupled to . CDC consumed di
A multi-tenant SaaS product has outgrown one database. You must shard. How do you choose the partition key, and what makes this decision so expensive to get wrong?
What the interviewer is testing Whether you exhaust cheaper options first, and whether you understand that a shard key is close to irreversible. First: do not s
A product catalogue page does 40,000 reads per second against a database that can serve 5,000. Walk me through the caching design, including what happens at 3 AM when the cache is empty.
What the interviewer is testing Whether you can design a cache including its failure modes, rather than saying "put Redis in front of it". The base design Cache
A serverless API works in testing and fails under load with connection errors. The database is at 5% CPU. Explain and fix.
The mechanism Serverless functions scale by creating independent execution environments , each with its own process and its own connection pool. Two hundred con
A service writes to its database and then publishes an event to Kafka. Sometimes consumers see an event for a record that does not exist, and sometimes a record exists with no event. Why, and how do you fix it?
What the interviewer is testing Recognition of the dual write problem — one of the most common defects in event driven systems and one that testing rarely catch
Anomalous access to a customer database is detected. Walk me through the first day, and say what determines whether you can answer the regulator.
The first hours Declare an incident and assign command. Named commander who does not debug, operations lead, communications lead, scribe. Security incidents add
TSB's 2018 core banking migration moved 1.9 million customers in a single weekend and failed publicly. What would you have required before approving that cutover?
The case, as publicly reported In April 2018 TSB migrated from a platform rented from Lloyds Banking Group to Proteo4UK, built by its parent Banco Sabadell. The
You are asked to give an internal AI agent access to the customer database, the ticketing system and outbound email so it can resolve support tickets. What is your response?
What the interviewer is testing Whether you recognise a specific and well documented security pattern, and whether you can propose a workable design instead of
You are asked to lead a migration of 300 applications to cloud. What happens in the first ninety days?
Days 1–30: discovery, and the foundation in parallel Discovery from evidence, not interviews. Network flow logs for dependencies (the only trustworthy source),
Your search index and your database disagree — some products appear in search that were deleted, and some new ones never appear. How do you make this reliable?
Why it drifts Almost always a dual write : the application writes to the database and then to the search index as two independent operations. One can succeed an
A team wants to move a workload from PostgreSQL to a document store because "the schema keeps changing". What do you ask?
The questions 1. What is actually changing — the shape, or the schema management process? "The schema keeps changing" usually means migrations are painful, not
Database Migration
Moving engines, versions and schemas without losing data or uptime.
Cloud Migration
Per-application disposition, sequencing and the capability change underneath.
Data Migration Strategies
Backfill, dual-write, reconciliation and verification.
Database Performance
Plans, indexes, contention and the pool in front of the database.
Migration Risk
Bounding blast radius, staging by cohort, and honest readiness reporting.
Zero-Downtime Migration
Expand, migrate, contract — and the contract phase that never happens.
Change Data Capture
Turning a database's replication log into a stream, and its coupling risk.
Embeddings
Dense representations, model coupling and the migration they imply.