Posts about spanner. ← All posts
Notes from contributing to Google's open-source Spanner Migration Tool (HarbourBridge). Where to start reading the codebase, where the load-bearing logic lives, and the parts that look simple but aren't.
Spanner partitions by primary-key range. A monotonically-increasing PK like a timestamp or UUID-v1 funnels all writes to one server. The fix changes everything from your sequence strategy to your tenant model.
Interleaving a child table into its parent co-locates the rows for fast joins. It also tightens coupling in ways that bite you on the next schema migration. A practitioner's decision matrix.
A bulk migration takes hours; the application can't be offline that long. CDC keeps the source and destination in sync while the bulk runs, and a quick cutover swaps traffic. The handoff between bulk and CDC is where most migrations go wrong.