asmhatreandClaude Sonnet 5
e478eafda3
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
67 lines
3.0 KiB
Java
67 lines
3.0 KiB
Java
package com.ankurm.expandcontract;
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import com.ankurm.expandcontract.customer.CustomerService;
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import org.junit.jupiter.api.Test;
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import org.junit.jupiter.api.io.TempDir;
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import org.springframework.jdbc.core.simple.JdbcClient;
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import java.nio.file.Path;
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import static org.assertj.core.api.Assertions.assertThat;
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/**
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* A trap this article's own first draft of the V2 migration fell into: adding
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* {@code email_address} is not the whole story of "expand" when the column being
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* retired is {@code NOT NULL}. Stage 4 code never writes "email" - so if "email" is
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* still mandatory when Stage 4 starts, every create fails, in production, the moment
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* that deploy reaches its first replica. The fix is one more line in the SAME
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* migration: {@code ALTER TABLE customers ALTER COLUMN email DROP NOT NULL}. See
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* docs/06-the-not-null-trap.md, and compare
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* {@link com.ankurm.expandcontract.customer.CustomerService#create} - the shipped
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* V2 migration (with the fix) is what every other test in this module runs against.
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*/
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class NotNullConstraintTrapTest {
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@Test
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void stage4FailsIfTheOldColumnIsStillMandatory(@TempDir Path tmp) throws Exception {
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Path db = tmp.resolve("not-null-trap");
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TestSupport.migrateTo(db, "1");
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JdbcClient jdbc = TestSupport.jdbcClient(db);
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Transcript t = Transcript.start("06-not-null-trap",
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"The NOT NULL trap: expand without relaxing the old column's constraint");
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// The NAIVE version of V2: add the column, backfill, stop there. This is
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// exactly V2 minus its last line.
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jdbc.sql("ALTER TABLE customers ADD COLUMN email_address VARCHAR(320)").update();
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jdbc.sql("UPDATE customers SET email_address = email WHERE email_address IS NULL").update();
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CustomerService stage4 = new CustomerService(jdbc, 4);
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Throwable thrown = null;
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try {
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stage4.create("Too Early", "[email protected]");
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} catch (Throwable ex) {
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thrown = ex;
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}
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t.section("Stage 4 create() against the NAIVE migration (no DROP NOT NULL)");
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assertThat(thrown).isNotNull();
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Throwable root = thrown;
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while (root.getCause() != null) {
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root = root.getCause();
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}
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t.line(thrown.getClass().getName() + ": " + thrown.getMessage());
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t.line("root cause: " + root.getClass().getName() + ": " + root.getMessage());
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assertThat(root.getMessage()).contains("NULL not allowed for column \"EMAIL\"");
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t.section("Stage 4 create() against the SHIPPED V2 migration (DROP NOT NULL included)");
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Path fixedDb = tmp.resolve("not-null-fixed");
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TestSupport.migrateTo(fixedDb, "2");
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CustomerService fixedStage4 = new CustomerService(TestSupport.jdbcClient(fixedDb), 4);
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long id = fixedStage4.create("On Time", "[email protected]");
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var result = fixedStage4.findById(id).orElseThrow();
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t.line(result.toString());
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assertThat(result.email()).isEqualTo("[email protected]");
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t.write();
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}
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}
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