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One free scan finds every outdated or missing driver and matches the right update for your exact hardware.Free scan · exact hardware matchThere is no single documented duration for a Redis Sentinel failover, and no measured result or test setup is available here to substantiate a first-person timing claim. The elapsed time depends on when Sentinels detect a failure, whether they can agree and authorize a failover, how quickly a replica is promoted and the topology reconfigured, and when clients reconnect and recover.
What counts as a failover’s duration?
A timing result is meaningful only when its start and end events are explicit. Measuring from a process crash to replica promotion answers a different question from measuring from the first missed response to successful client writes. Redis documents Sentinel’s mechanisms and configuration, but does not give a universal end-to-end Sentinel failover SLA. Redis: High availability with Redis Sentinel
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For an operationally useful measurement, define the interval you care about: for example, failure injection to successful writes through the application’s normal connection path. Report intermediate timestamps too, if available, so detection, promotion, and client recovery are not mistaken for one event.
What determines how long Sentinel takes?
Failure detection and Sentinel agreement
Each Sentinel first evaluates reachability locally. It marks an instance SDOWN after it has received no valid PING response for the configured down-after-milliseconds interval. Sentinel marks it ODOWN after enough Sentinels agree, according to the configured quorum. Proceeding with failover also requires authorization from a majority of Sentinel processes. Consequently, reaching the local detection threshold does not guarantee an immediate failover if Sentinels cannot communicate or obtain the required votes. Redis: High availability with Redis Sentinel
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Replica choice, promotion, and reconfiguration
After authorization, Sentinel selects a suitable replica and promotes it, then reconfigures the other replicas to follow the new primary. Selection can depend on the replica’s disconnection time, configured priority, replication offset, and run ID. The parallel-syncs setting controls how many replicas Sentinel reconfigures to follow the promoted replica at once; this affects replica availability during synchronization, not just the instant of promotion. Redis Sentinel configuration source
Client recovery
A promoted primary does not by itself establish when an application is usable again. The observed end time depends on the client’s discovery, reconnection, retry, and write behavior. A report that ends at promotion should not be described as time until client recovery.
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Why the configured timeout is not a failover guarantee
failover-timeout is a control parameter used for several parts of the failover process, including retry timing after an attempt and waiting periods. It is not a promise that an entire Sentinel failover will complete within that number of milliseconds. Redis: High availability with Redis Sentinel
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Redis’s unstable-branch Sentinel implementation declares a 1-second ping period, a 30-second default down-after-milliseconds threshold, and a 180-second default failover timeout. These are implementation defaults in the inspected unstable branch, not measured failover durations or universal settings across Redis versions and deployments. Use the deployed Redis version and effective Sentinel configuration when interpreting timings. Redis Sentinel source, unstable branch
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Do not confuse Sentinel failover with the FAILOVER command
Redis documents that coordinated failovers initiated with the FAILOVER command “typically happen in less than a second,” but says they may take longer under heavy write traffic or when the replica is behind in consuming the replication stream. That statement describes the command’s coordinated failover context; it is not a guarantee for Sentinel’s full failure-detection-to-client-recovery interval. Redis: FAILOVER command
How to report a useful measurement
A reproducible timing report should make the setup and interval clear enough that readers can tell what the result represents. Include:
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- Redis version and the Sentinel topology, including Sentinel count and quorum.
- Effective timing settings, especially
down-after-milliseconds,failover-timeout, andparallel-syncs. - The failure trigger and relevant network conditions.
- Replica state, including replication lag or offset where available.
- Exact start and end markers, such as failure injection, promotion, and the first successful application write.
- Results across multiple runs if reporting a typical or variable duration, rather than implying one run is universal.
Without those details and an actual measurement, a specific number would be misleading. Official Redis documentation explains the mechanisms and the command-specific timing caveat, but does not provide a benchmark distribution for Sentinel end-to-end failover.
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