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
86 lines
3.7 KiB
Java
86 lines
3.7 KiB
Java
package com.ankurm.expandcontract;
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import com.ankurm.expandcontract.customer.Customer;
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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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* Deploy 4 (CONTRACT), in both directions. First the case that must work: once every
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* replica is confirmed on Stage 4 and the drop migration (V3) has run, Stage 4 code
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* keeps working exactly as before - it never referenced "email" to begin with. Second
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* the case that must fail loudly: a Stage 1, 2 or 3 instance that is somehow still
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* running against the post-drop schema (a rollback gone wrong, a forgotten canary)
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* gets a real SQL error the moment it tries to touch the column that no longer exists.
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* That failure is not a bug in this article's design - it is *why* Deploy 4 has to wait
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* for confirmation that the fleet is 100% on Stage 4 first. See
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* docs/09-the-contract-migration.md and docs/10-what-happens-if-you-drop-too-soon.md.
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*/
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class ContractSafetyTest {
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@Test
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void stage4KeepsWorkingAfterTheColumnIsDropped(@TempDir Path tmp) throws Exception {
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Path db = tmp.resolve("contract-ok");
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TestSupport.migrateTo(db, "2");
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JdbcClient jdbc = TestSupport.jdbcClient(db);
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Transcript t = Transcript.start("09-contract-safety",
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"Deploy 4 (CONTRACT): Stage 4 after the drop, and what breaks if you drop too soon");
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CustomerService stage4 = new CustomerService(jdbc, 4);
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long id = stage4.create("Annie Easley", "[email protected]");
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// Deploy 4b: drop the old column, live, with Stage 4 already the only code running.
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TestSupport.migrateTo(db, "latest");
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Customer afterDrop = stage4.findById(id).orElseThrow();
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t.section("Stage 4 read, after V3 dropped the email column");
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t.line(afterDrop.toString());
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assertThat(afterDrop.email()).isEqualTo("[email protected]");
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long postDropId = stage4.create("Mary Allen Wilkes", "[email protected]");
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Customer postDrop = stage4.findById(postDropId).orElseThrow();
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t.section("Stage 4 create + read, entirely after the drop");
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t.line(postDrop.toString());
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assertThat(postDrop.email()).isEqualTo("[email protected]");
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t.write();
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}
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@Test
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void stage1CodeFailsLoudlyIfItIsStillRunningAfterTheColumnIsDropped(@TempDir Path tmp) throws Exception {
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Path db = tmp.resolve("contract-too-soon");
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TestSupport.migrateTo(db, "latest");
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JdbcClient jdbc = TestSupport.jdbcClient(db);
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Transcript t = Transcript.start("10-drop-too-soon",
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"What a lingering Stage 1 instance sees if the drop runs before it is retired");
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CustomerService stage1 = new CustomerService(jdbc, 1);
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Throwable thrown = catchThrowable(() -> stage1.create("Too Late", "[email protected]"));
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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("Stage 1 create() after V3 dropped \"email\": " + thrown.getClass().getName());
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t.line("message: " + thrown.getMessage());
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t.line("root cause: " + root.getClass().getName() + ": " + root.getMessage());
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assertThat(root.getMessage()).contains("EMAIL").containsIgnoringCase("not found");
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t.write();
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}
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private static Throwable catchThrowable(org.assertj.core.api.ThrowableAssert.ThrowingCallable callable) {
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try {
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callable.call();
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return new AssertionError("expected an exception but none was thrown");
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} catch (Throwable t) {
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return t;
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}
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}
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}
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