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Fail over to a recovered database when the active one is inoperable - #4765
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When the active database turned unhealthy with no failover target, the failover was never retried: a database that became usable later, e.g. one with a lower weight than the active one, was ignored by both the health event handler and failback, so commands kept failing until a manual setActiveDatabase(), also after the failure turned permanent. Retry the failover when another database turns healthy, and when a command cannot get a connection from an inoperable active database, which also covers a target whose grace period ended without an event and configurations with health checks disabled. Both paths share one implementation, so a failed attempt counts the same way for health events and commands. The test that relied on two consecutive raw failures with a usable candidate now expects failover on the first failed command.
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Test Results 206 files ±0 206 suites ±0 7m 48s ⏱️ -6s Results for commit 0faf241. ± Comparison against base commit 5079fbd. This pull request removes 1 and adds 1 tests. Note that renamed tests count towards both.♻️ This comment has been updated with latest results. |
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Reviewed by Cursor Bugbot for commit 24ed568. Configure here.
| private void failoverIfActiveInoperable() { | ||
| Database current = activeDatabase; | ||
| if (!current.isHealthy()) switchToHealthyDatabase(SwitchReason.HEALTH_CHECK, current); | ||
| } |
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Failover can skip the grace period
Medium Severity
failoverIfActiveInoperable() switches away from an inoperable active database without calling setGracePeriod(). Health status is published to isHealthy() before onHealthStatusChange runs, so a command (or a peer HEALTHY event) can move activeDatabase first. The later UNHEALTHY handler then sees the database is no longer active and skips grace entirely. That database is eligible again as soon as it reports healthy, which undermines the flapping protection grace is meant to provide.
Additional Locations (1)
Reviewed by Cursor Bugbot for commit 24ed568. Configure here.
A command that finds the active database inoperable while another one is operable took activeDatabaseChangeLock, so commands queued behind a switch, which can include a validation PING under that lock. Commands now only try the lock and skip when a switch is in progress: the command fails anyway and the next failing command re-evaluates the state. The health event path is unchanged.
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2 participants
Fixes #4764
Follow-up to #4755
What
Retries a failover that found no target, so
MultiDbClientswitches to a database that becomes usable later, whatever its weight, afterJedisTemporaryNotAvailableException.Why
#4756 keeps the health checks alive after a total outage. The remaining part of #4755 is that when the active database is unhealthy and no other one is usable, the failover is never retried. A lower-weight database turning healthy is ignored (failback only promotes higher weights), a candidate that was still in its grace period is never picked up because nothing announces the end of the grace period, and with health checks disabled there are no events at all. The client stays on the failing database until a manual
setActiveDatabase().Changes
MultiDbConnectionProvider: a singlefailoverIfActiveInoperable()switches away from an inoperable active database to the best operable one. When there is none, the failure counts as a failover attempt as before.assertOperability()when a command cannot get a connection from an inoperable active database. A failed attempt is counted the same way in both.forceActiveDatabase()still pins the database, because the other databases are in grace for the pin duration.userCommand_connectionExceptions_thenMultipleTemporary_thenPermanent_inOrdernow expects the first failed command to fail over; the manual-switch test becomes...failsOverAutomatically_healthCheckDriven; unit tests for health events counting as attempts, the command trigger after a grace period, and the forced pin.docs/failover.md: describes the recovery after a failed failover.Notes
assertOperability(), so only the health event covers them.Note
Medium Risk
Changes core MultiDb failover selection and recovery timing; mistakes could cause unexpected database switches or stuck routing, though behavior is heavily tested and forced pinning is preserved.
Overview
MultiDbClient now retries failover when the active database is unusable but no target was available earlier, so clients can recover automatically—even after
JedisPermanentlyNotAvailableException—without manualsetActiveDatabase().MultiDbConnectionProvideraddsfailoverIfActiveInoperable(), which moves traffic to the best operable database regardless of weight. It runs when a non-active database becomes healthy (health listener) and fromassertOperability()when a command cannot get a connection from the active DB (usingtryLockso the failing command does not block). Failed attempts still count towardmaxNumFailoverAttempts; exceeding the limit only chooses temporary vs permanent exceptions, it no longer blocks later recovery.forceActiveDatabase()pinning is unchanged (alternates stay in grace).docs/failover.mddocuments automatic switch-back when any database becomes usable again and softens permanent-exception guidance to alert rather than shut down.Tests now expect command-triggered failover to the secondary, automatic failover when only a lower-weight DB recovers after a total outage, plus unit coverage for health-driven attempt counting, post-grace
assertOperability, and forced-active behavior.Reviewed by Cursor Bugbot for commit 0faf241. Bugbot is set up for automated code reviews on this repo. Configure here.