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
parent 22c30d4a5b
commit e478eafda3
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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