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docs: fix outdated Region size in multi-AZ deployment doc #24204

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docs: fix outdated Region size in multi-AZ deployment doc #24204

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2 changes: 1 addition & 1 deletion multi-data-centers-in-one-city-deployment.md
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Expand Up @@ -104,7 +104,7 @@ 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 TiKV instance numbers, 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 and the size of each Region is 256 MiB 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 TiKV instance numbers, 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.

@coderabbitai coderabbitai Bot Oct 7, 2026

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📐 Maintainability & Code Quality | 🟡 Minor | ⚡ Quick win

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git diff --unified=5 6ba85765e2f9e8d080a7f1789a3b46641a09d960 75a0a4aa8a4b955f6868ef1dadb80159d527cfd8 -- multi-data-centers-in-one-city-deployment.md
sed -n '1235,1252p' tikv-configuration-file.md
find .. -name AGENTS.md -o -name CONTRIBUTING.md

Repository: pingcap/docs

Length of output: 3253

Describe 256 MiB as an estimate for newly split Regions.

The configuration reference describes region-split-size as an estimate for newly split Regions, not a fixed size for every Region. Update this sentence:

Suggested fix 
-TiKV is a Multi-Raft system where data is divided into Regions and the size of each Region is 256 MiB 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 TiKV instance numbers, 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. The default estimated size for newly split Regions is 256 MiB. 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 TiKV instance numbers, 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.
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TiKV is a Multi-Raft system where data is divided into Regions and the size of each Region is 256 MiB 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 TiKV instance numbers, 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. The default estimated size for newly split Regions is 256 MiB. 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 TiKV instance numbers, 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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