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docs: fix outdated Region size in multi-AZ deployment doc (#24204) #24557

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ti-chi-bot merged 1 commit into from
Oct 27, 2026
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docs: fix outdated Region size in multi-AZ deployment doc (#24204) #24557

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2 changes: 1 addition & 1 deletion multi-data-centers-in-one-city-deployment.md
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Expand Up @@ -103,7 +103,7 @@ The following example assumes that three AZs (AZ1, AZ2, and AZ3) are located in

#### TiKV labels

TiKV is a Multi-Raft system where data is divided into Regions and the size of each Region is 96 MB by default. Three replicas of each Region form a Raft group. For a TiDB cluster of three replicas, because the number of Region replicas is independent of the number of TiKV instances, three replicas of a Region are only scheduled to three TiKV instances. This means that even if the cluster is scaled out to have N TiKV instances, it is still a cluster of three replicas.
TiKV is a Multi-Raft system where data is divided into Regions. By default, the [estimated size for a newly split Region](/tikv-configuration-file.md#region-split-size) is 256 MiB for TiDB v8.4.0 and later versions, and 96 MiB for TiDB versions earlier than v8.4.0. Three replicas of each Region form a Raft group. For a TiDB cluster of three replicas, because the number of Region replicas is independent of the number of TiKV instances, three replicas of a Region are only scheduled to three TiKV instances. This means that even if the cluster is scaled out to have N TiKV instances, it is still a cluster of three replicas.

Because a Raft group of three replicas tolerates only one replica failure, even if the cluster is scaled out to have N TiKV instances, this cluster still tolerates only one replica failure. Two failed TiKV instances might cause some Regions to lose replicas and the data in this cluster is no longer complete. SQL requests that access data from these Regions will fail. The probability of two simultaneous failures among N TiKV instances is much higher than the probability of two simultaneous failures among three TiKV instances. This means that the more TiKV instances the Multi-Raft system is scaled out to have, the less the availability of the system.

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