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asmhatreandClaude Sonnet 5 e478eafda3 Add db-migrations-expand-contract: zero-downtime schema migrations proven with a real 4-deploy rolling run
Companion code for Zero-Downtime Database Migrations: Expand-Contract in Practice
with Spring Boot: a full expand/migrate-writes/migrate-reads/contract sequence run
as an actual rolling deploy across two live replicas, with a load generator sending
continuous HTTP traffic through all four deploys (99.98% success, every residual
error traced to a root cause rather than left unexplained). Findings include a real
NOT NULL constraint trap in the expand migration, a backfill-window bug in the read
switch, H2's AUTO_SERVER=TRUE single-point-of-failure behavior under a rolling
restart, the drain-before-SIGTERM fix needed to close a health-check gap during
graceful shutdown, and H2 silently discarding a concurrently committed INSERT during
an ALTER TABLE ADD/DROP COLUMN rebuild - confirmed, by primary source, to be an
H2-specific behavior rather than a property of the technique itself.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_019Fb7vW8vLyLKngBc4R3huA
2026-09-16 19:22:48 +00:00

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Load generator summary
=======================
Total requests: 30911
Successful: 30905
Errors: 6
By phase:
04a-stage4-soak ok=2130 error=0
04b-contract-migration ok=336 error=0
04a-deploy-stage4-rollout ok=4147 error=0
03-stage3-soak ok=2116 error=0
03-deploy-stage3-rollout ok=4645 error=0
00-baseline-soak ok=1893 error=0
05-final-soak ok=7118 error=4
- read-http-404 2
- update-http-404 2
02-stage2-soak ok=2068 error=0
01-expand-migration ok=1773 error=1
- read-http-404 1
02-deploy-stage2-rollout ok=4679 error=1
- update-http-404 1