How To Choose Snapshot Mode

The rule is simple: use none unless the source is live enough that cross-table inconsistency matters.

Choose none when

• the source is static
• writes are already paused
• you want the fastest run
• per-table or per-chunk parallelism matters more than a single consistent snapshot

Choose single_tx when

• the source stays live during the migration
• you need one point-in-time view across tables
• you accept slower sequential reads in exchange for consistency

Source limits

• MySQL: supported
• MariaDB: supported
• MSSQL: supported; pgferry enables ALLOW_SNAPSHOT_ISOLATION only when it is not already on and the login may ALTER DATABASE (or it is already on without needing ALTER)
• SQLite: unsupported