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[TiDB] Add new mode option prefer-leader for tidb_replica_read. #12865

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merged 4 commits into from
Feb 10, 2023
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[TiDB] Add new mode option prefer-leader for tidb_replica_read. #12865

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9cd5c6c
Add new mode option `prefer-leader` for `tidb_replica_read`.
LykxSassinator Feb 1, 2023
a746541
Polish docs.
LykxSassinator Feb 1, 2023
3f88a19
Update develop/dev-guide-use-follower-read.md
LykxSassinator Feb 3, 2023
78bd607
Update follower-read.md
LykxSassinator Feb 3, 2023
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5 changes: 3 additions & 2 deletions develop/dev-guide-use-follower-read.md
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Expand Up @@ -33,7 +33,7 @@ aliases: ['/zh/tidb/dev/use-follower-read']
<SimpleTab>
<div label="SQL">

在 SQL 中，你可以将变量 `tidb_replica_read` 的值（默认为 `leader`）设置为 `follower`、 `leader-and-follower`、 `closest-replicas` 或 `closest-adaptive` 开启 TiDB 的 Follower Read 功能：
在 SQL 中，你可以将变量 `tidb_replica_read` 的值（默认为 `leader`）设置为 `follower`、`leader-and-follower`、`prefer-leader`、`closest-replicas` 或 `closest-adaptive` 开启 TiDB 的 Follower Read 功能：

```sql
SET [GLOBAL] tidb_replica_read = 'follower';
Expand All @@ -52,7 +52,8 @@ public enum FollowReadMode {
FOLLOWER("follower"),
LEADER_AND_FOLLOWER("leader-and-follower"),
CLOSEST_REPLICA("closest-replica"),
CLOSEST_ADAPTIVE("closest-adaptive");
CLOSEST_ADAPTIVE("closest-adaptive"),
PREFER_LEADER("prefer-leader");

private final String mode;

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1 change: 1 addition & 0 deletions follower-read.md
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Expand Up @@ -35,6 +35,7 @@ set [session | global] tidb_replica_read = '<目标值>';
- 当设置为默认值 `leader` 或者空字符串时，TiDB 会维持原有行为方式，将所有的读取操作都发送给 leader 副本处理。
- 当设置为 `follower` 时，TiDB 会选择 Region 的 follower 副本完成所有的数据读取操作。
- 当设置为 `leader-and-follower` 时，TiDB 可以选择任意副本来执行读取操作，此时读请求会在 leader 和 follower 之间负载均衡。
- 当设置为 `prefer-leader` 时，TiDB 会优先选择 leader 副本执行读取操作。当 leader 副本的处理速度明显变慢时，例如由于磁盘或网络性能抖动，TiDB 将选择其他可用的 follower 副本来执行读取操作。
- 当设置为 `closest-replicas` 时，TiDB 会优先选择分布在同一可用区的副本执行读取操作，对应的副本可以是 leader 或 follower。如果同一可用区内没有副本分布，则会从 leader 执行读取。
- 当设置为 `closest-adaptive` 时：

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2 changes: 1 addition & 1 deletion system-variables.md
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Expand Up @@ -2962,7 +2962,7 @@ EXPLAIN FORMAT='brief' SELECT COUNT(1) FROM t WHERE a = 1 AND b IS NOT NULL;
- 作用域：SESSION | GLOBAL
- 是否持久化到集群：是
- 默认值：`leader`
- 可选值：`leader`，`follower`，`leader-and-follower`，`closest-replicas`，`closest-adaptive`
- 可选值：`leader`，`follower`，`leader-and-follower`，`prefer-leader`，`closest-replicas`，`closest-adaptive`
- 这个变量用于控制 TiDB 的 Follower Read 功能的行为。
- 关于使用方式与实现原理，见 [Follower Read](/follower-read.md)。

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