Geo-Distributed Deployment Topology

This document takes the typical architecture of three data centers (DC) in two cities as an example, and introduces the geo-distributed deployment architecture and the key configuration. The cities used in this example are Shanghai (referred to as sha) and Beijing (referred to as bja and bjb).

Topology information

Instance	Count	Physical machine configuration	BJ IP	SH IP	Configuration
TiDB	5	16 VCore 32GB * 1	10.0.1.1 10.0.1.2 10.0.1.3 10.0.1.4	10.0.1.5	Default port Global directory configuration
PD	5	4 VCore 8GB * 1	10.0.1.6 10.0.1.7 10.0.1.8 10.0.1.9	10.0.1.10	Default port Global directory configuration
TiKV	5	16 VCore 32GB 2TB (nvme ssd) * 1	10.0.1.11 10.0.1.12 10.0.1.13 10.0.1.14	10.0.1.15	Default port Global directory configuration
Monitoring & Grafana	1	4 VCore 8GB * 1 500GB (ssd)	10.0.1.16		Default port Global directory configuration

Topology templates

The geo-distributed topology template

For detailed descriptions of the configuration items in the above TiDB cluster topology file, see Topology Configuration File for Deploying TiDB Using TiUP.

Key parameters

This section describes the key parameter configuration of the TiDB geo-distributed deployment.

TiKV parameters

The gRPC compression format (none by default):
To increase the transmission speed of gRPC packages between geo-distributed target nodes, set this parameter to gzip.
```
server.grpc-compression-type: gzip
```
The label configuration:
Since TiKV is deployed across different data centers, if the physical machines go down, the Raft Group might lose three of the default five replicas, which causes the cluster unavailability. To address this issue, you can configure the labels to enable the smart scheduling of PD, which ensures that the Raft Group does not allow three replicas to be located in TiKV instances on the same machine in the same cabinet of the same data center.

The TiKV configuration:

The same host-level label information is configured for the same physical machine.

config:
  server.labels:
    zone: bj
    dc: bja
    rack: rack1
    host: host2

To prevent remote TiKV nodes from launching unnecessary Raft elections, it is required to increase the minimum and maximum number of ticks that the remote TiKV nodes need to launch an election. The two parameters are set to 0 by default.
```
raftstore.raft-min-election-timeout-ticks: 50
raftstore.raft-max-election-timeout-ticks: 60
```

Note

Using raftstore.raft-min-election-timeout-ticks and raftstore.raft-max-election-timeout-ticks to configure larger election timeout ticks for a TiKV node can significantly decrease the likelihood of Regions on that node becoming Leaders. However, in a disaster scenario where some TiKV nodes are offline and the remaining active TiKV nodes lag behind in Raft logs, only Regions on this TiKV node with large election timeout ticks can become Leaders. Because Regions on this TiKV node must wait for at least the duration set by `raftstore.raft-min-election-timeout-ticks' before initiating an election, it is recommended to avoid setting these values excessively large to prevent potential impact on the cluster availability in such scenarios.

PD parameters

The PD metadata information records the topology of the TiKV cluster. PD schedules the Raft Group replicas on the following four dimensions:
```
replication.location-labels: ["zone","dc","rack","host"]
```
To ensure high availability of the cluster, adjust the number of Raft Group replicas to be 5:
```
replication.max-replicas: 5
```
Forbid the remote TiKV Raft replica being elected as Leader:
```
label-property:
      reject-leader:
        - key: "dc"
          value: "sha"
```
Note
Since TiDB 5.2, the label-property configuration is not supported by default. To set the replica policy, use the placement rules.

For the further information about labels and the number of Raft Group replicas, see Schedule Replicas by Topology Labels.