How long does a database migration take?
Migration timeline depends on three factors: data volume (a 10GB database can be migrated in hours; a 10TB database may require days for the initial load plus a multi-day parallel running period), acceptable downtime (zero-downtime migrations using CDC-based replication take longer to set up and validate than a simple dump-restore with a maintenance window), and schema complexity (a migration involving stored procedures, custom data types, and complex foreign key relationships requires more planning and testing than a simple table migration). Typical timelines: a MySQL to PostgreSQL migration of a 50GB database with 2-hour acceptable downtime: 2-4 weeks (1-2 weeks for schema conversion and testing, 1-2 weeks for migration execution and validation). A zero-downtime migration of the same database: 3-6 weeks (additional time for CDC setup, dual-write implementation, and extended parallel running). ClickMasters delivers a timeline estimate in the migration assessment engagement before any migration work begins.
What is CDC (Change Data Capture) and why is it used for zero-downtime migration?
Change Data Capture reads the database's transaction log (binary log on MySQL, WAL on PostgreSQL) and streams every insert, update, and delete as an event in real time, with the exact data that changed. For zero-downtime migration: the initial data load copies all existing data to the target database. Once the initial load completes, CDC streams every subsequent change from the source to the target keeping the target in near-real-time sync while the source remains live. When the target has caught up (replication lag < 1 second), the application is cut over to the target database typically a few seconds of read-only mode or a brief maintenance window to ensure the final transactions are applied. After cutover, the source is kept in read-only mode for a parallel running period to validate data consistency. AWS DMS implements CDC for supported source databases (MySQL, PostgreSQL, Oracle, SQL Server, MongoDB). Debezium is the open-source alternative for teams managing their own CDC infrastructure.
What are the risks of a database migration and how do you mitigate them?
The primary risks in a database migration: data loss (rows not migrated or silently corrupted during migration mitigated by row count reconciliation and checksum validation after every migration stage), downtime (migration takes longer than planned mitigated by rehearsing the migration procedure multiple times in staging with production-scale data before the production migration), application incompatibility (application code makes database-specific assumptions that break on the target mitigated by running the full application test suite against the target database before cutover), and performance regression (the target database performs worse for specific queries than the source mitigated by query benchmarking in staging before cutover). ClickMasters runs a full dress rehearsal of the production migration in staging using a restored production snapshot before committing to the production migration date. This dress rehearsal typically surfaces 80-90% of issues.
Do I need to update my application code during a database migration?
It depends on the migration type. A platform migration (MySQL to PostgreSQL) typically requires application changes: PostgreSQL's boolean type uses TRUE/FALSE (MySQL uses 1/0), auto-increment is SERIAL or bigserial (not AUTO_INCREMENT), and some MySQL-specific SQL syntax (GROUP BY behaviour, string functions) is different in PostgreSQL. ClickMasters audits all database queries against the PostgreSQL compatibility list as part of the assessment. A schema migration (re-architecting the data model) always requires application changes the ORM models and query code must be updated to use the new schema. A cloud migration (MySQL on-premises to RDS MySQL) typically requires no application changes same database engine, same SQL, only the connection string changes. ClickMasters scopes the application change requirement in the migration assessment so the engineering team can plan the development work in parallel with the migration preparation.
