PostgreSQL Zero-Downtime Migration & Lock Risk Analyzer

Detect dangerous table locks (ACCESS EXCLUSIVE), identify migration downtime risks, and generate safe zero-downtime SQL rewrites.

Try High-Risk Migration:
Lock Level: SHARE

Blocks all INSERT, UPDATE, and DELETE writes while building the index (can take hours on large tables).

• Creating an index without CONCURRENTLY blocks all write traffic for the duration of the build.

Understanding PostgreSQL Lock Modes in Production

In high-throughput production PostgreSQL databases, running innocent-looking DDL migrations like ALTER TABLE or CREATE INDEX can acquire an ACCESS EXCLUSIVE lock. This blocks all incoming read and write queries, causing connection pool exhaustion, request timeouts, and cascading downtime across application microservices.

Zero-Downtime Migration Rules

  • Always use CREATE INDEX CONCURRENTLY: Regular index creation blocks table writes for the entire duration of the B-tree scan. CONCURRENTLY builds the index in two passes without blocking writes.
  • Add Foreign Keys with NOT VALID: Adding a foreign key constraint normally validates all rows under an exclusive lock. Splitting into ADD CONSTRAINT ... NOT VALID followed by VALIDATE CONSTRAINT prevents write locks.
  • Always set a low lock_timeout: Setting SET lock_timeout = '2s'; ensures that if your migration cannot immediately acquire a lock due to an active query, it fails quickly instead of queueing behind it and blocking all subsequent traffic.