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Backport #4745 to 8.0.x: Update failover.md and some javadoc - #4772
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* - update failover.md and some javadoc * - fix javadoc (cherry picked from commit 2861d3e)
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| ```java | ||
| // Pin redis-east as the active database for the next 10 minutes | ||
| client.forceActiveDatabase(endpoint, Duration.ofMinutes(10).toMillis()); |
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In the documented scenario, endpoint is a new HostAndPort equal to—but not identical to—the endpoint stored during configuration. MultiDbConnectionProvider.forceActiveDatabase() excludes the target using entry.getKey() != endpoint, so it also puts this target into the grace period; the subsequent validation then throws JedisValidationException instead of pinning it. Either fix that identity comparison or demonstrate obtaining the stored endpoint (for example from getDatabaseEndpoints()) before recommending this call.
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| MultiDbConfig config = MultiDbConfig.builder() | ||
| .database(east, 1.0f, clientConfig) | ||
| .database(west, 0.5f, clientConfig) | ||
| .initializationPolicy(InitializationPolicy.BuiltIn.ONE_AVAILABLE) // start as soon as one database is reachable | ||
| .build(); |
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With multiple health-checked databases, ONE_AVAILABLE does not necessarily let build() return as soon as any database is reachable. waitForInitializationPolicy() sorts endpoints by weight and waits for each specific endpoint in that order, so a slow or unreachable high-weight endpoint blocks initialization even when a lower-weight endpoint has already reported healthy. This comment should not promise immediate startup unless the provider is changed to react to health results globally.
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| - **Health Check Integration**: If health checks are configured, the new database will be monitored according to the configured health check strategy | ||
| - **Duplicate Prevention**: Attempting to add an endpoint that already exists will throw a `JedisValidationException` | ||
| - **Weight-Based Selection**: The new database participates in weight-based active database selection according to its configured weight | ||
| - **Weight-Based Selection**: The new database participates in weight-based active database selection according to its configured weight. Adding a database does not switch the active database by itself; if the new database has the highest weight, the next periodic failback check will switch to it |
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When failbackSupported(false) is configured, MultiDbConnectionProvider never schedules periodicFailbackCheck(), so adding a new highest-weight database will not switch to it on any later check; it remains inactive until a failover or manual switch occurs. Qualify this behavior with failback being enabled so users who disabled automatic failback do not wait for a switch that cannot happen.
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| If you already have a configured strategy instance, `healthCheckStrategy(HealthCheckStrategy)` wraps it in a supplier for you. | ||
| The same instance is then reused for every database that shares that `DatabaseConfig`, so make sure it is thread-safe. |
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Thread safety alone does not make sharing this strategy instance safe. Every HealthCheckImpl treats its strategy as owned and calls strategy.close() when its database is removed or its client closes, so if the same DatabaseConfig is reused across clients—or the same instance is otherwise shared—closing one health check closes the resources still used by the others. Recommend a supplier that creates a distinct instance per database/client, or explicitly document the shared lifecycle hazard.
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2 participants
Clean cherry-pick of
2861d3e1a(#4745) onto8.x.Rewrites
docs/failover.mdand updates theMultiDbConfigandHealthCheckStrategyJavadocs. Documentation only, no code changes.Backport notes
8.x.docs/failover.mdhunk applies. Merge this one first.Testing
formatter:validatepasses.failover.mdanchors.Note
Low Risk
Documentation and Javadoc updates only; no production code behavior changes.
Overview
Major expansion and correction of
docs/failover.mdforMultiDbClient/MultiDbConfig: reorganized guide outline, documents the shorterdatabase(endpoint, weight, clientConfig)builder overload, and clarifies that the circuit breaker uses a time-based sliding window (seconds) with both minimum failures and failure rate required to trip.New or substantially added topics include failover/failback settings (defaults such as 2 min failback interval and 1 min grace period), initialization policies (7.3+), behavior when no healthy database exists (temporary vs permanent exceptions), health-check probe parameters and policies, updated fallback exception list (
ConnectionFailoverException),DatabaseSwitchEvent/SwitchReason, manualsetActiveDatabasevsforceActiveDatabase, and sharper runtime add/remove/query semantics.Javadoc-only fixes in
MultiDbConfig(builder example, sliding window in seconds, failback/grace default descriptions) andHealthCheckStrategy.Configbuilder (documented defaults 5000 ms interval and 500 ms between probes). No runtime logic changes.Reviewed by Cursor Bugbot for commit b057c29. Bugbot is set up for automated code reviews on this repo. Configure here.