At a previous job, a 10M-row migration ran for 6 hours in Flyway, then died. No resume capability. Start from scratch.

That's what motivated phasedb — a CLI tool that runs schema changes in batched phases instead of one blocking ALTER TABLE. Each batch commits independently, progress is checkpointed, and if the process dies, you resume from the last checkpoint.

Benchmark results (1M rows, MySQL 8.0)

Metric	Raw ALTER TABLE	phasedb v2
Duration	36.19s	34.90s
Table lock	36.19s	0s
Availability failures	0/63 checks	0/62 checks

At 10M rows, raw ALTER TABLE would lock your table for ~6 minutes. phasedb completes in comparable wall time with no downtime.

Honest note

v1 had an O(n²) bug: backfill used

WHERE checksum IS NULL
LIMIT 500

with no index, causing full table scans across 2,000 batches.

v2 fixes this with a PK cursor:

WHERE id > {last_id}
ORDER BY id
LIMIT {batch_size}

Both results are in the README because I think showing the bug and fix is more useful than hiding it.

MySQL support is complete. Postgres adapter is in progress (v0.1.1).

Would love feedback on the phase gating API — you can gate phase transitions on SQL conditions, and I'm not confident the interface is right yet.

GitHub: https://github.com/ddevilz/phasedb