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Deprecate config item max-memory and add items server-memory-quota and memory-usage-alarm-ratio #4977

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Deprecate config item max-memory and add items server-memory-quota and memory-usage-alarm-ratio #4977

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wshwsh12 committed Nov 30, 2020
commit ecab1c852bf585babf0dc04cebe357dfd83e1d26
7 changes: 7 additions & 0 deletions system-variables.md
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Expand Up @@ -956,3 +956,10 @@ explain select * from t where age=5;
+-------------------------------+------------+-----------+-----------------------------+-------------------------------+
3 rows in set (0.00 sec)
```

### `tidb_memory_usage_alarm_ratio`

- 作用域：SESSION
- 默认值：0.8
- TiDB 内存使用占总内存的比例超过一定阈值时会报警。该功能的详细介绍和使用方法可以参考 [`memory-usage-alarm-ratio`](/tidb-configuration-file.md#memory-usage-alarm-ratio) 。
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- 该变量的初始值由配置项 [`memory-usage-alarm-ratio`](/tidb-configuration-file.md#memory-usage-alarm-ratio) 配置。
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17 changes: 13 additions & 4 deletions tidb-configuration-file.md
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Expand Up @@ -278,11 +278,20 @@ TiDB 配置文件比命令行参数支持更多的选项。你可以在 [config/
+ 默认值：0
+ 默认值为 0 表示使用机器上所有的 CPU；如果设置成 n，那么 TiDB 会使用 n 个 CPU 数量。

### `max-memory`
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可能有用户还在使用这个配置项，废弃这个配置项是否需要说明一下呢？

  • 不推荐使用/已不能使用/已被新的配置项替代？
  • 从哪个版本废弃的？

### `server-memory-quota`

+ Prepare cache LRU 使用的最大内存限制。当 Prepare cache LRU 的内存使用超过 `performance.max-memory * (1 - prepared-plan-cache.memory-guard-ratio)` 时，会剔除 LRU 中的元素。
+ 默认值：0
+ 这个配置在 `prepared-plan-cache.enabled` 为 `true`（默认值）的情况才会生效。当 LRU 的 size 大于 `prepared-plan-cache.capacity` 时，也会剔除 LRU 中的元素。
+ TiDB 内存使用限制，单位为字节。
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+ 默认值：0
+ 默认值为 0 表示无内存限制。

### `memory-usage-alarm-ratio`

+ TiDB 内存使用占总内存的比例超过一定阈值时会报警。该配置项的有效范围为 0 到 1。如果配置该选项为 0 或 1，则表示关闭内存阈值报警功能。
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+ 默认值：0.8
+ 当内存阈值报警功能开启时，如果配置项 [`server-memory-quota`](/tidb-configuration-file.md#server-memory-quota) 未设置，则内存报警阈值为 `memory-usage-alarm-ratio * 系统内存大小`；如果 `server-memory-quota` 被设置且大于 0，则内存报警阈值为 `memory-usage-alarm-ratio * server-memory-quota`。
+ 当 TiDB 检测到内存使用超过了阈值，则会认为存在 OOM 的风险，会将当前正在执行的所有 SQL 语句中内存使用最高的 10 条语句和运行时间最长的 10 条语句以及 heap profile 记录到目录 [`tmp-storage-path/record`](/tidb-configuration-file.md#tmp-storage-path) 中，并输出一条包含关键字 `tidb-server has the risk of OOM` 的日志。
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+ 该值作为系统变量 [`tidb_memory_usage_alarm_ratio`](/system-variables.md#tidb_memory_usage_alarm_ratio) 的初始值。

### `txn-total-size-limit`

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