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# 配置项修改介绍
## 设置方式
* 使用sql语句修改【推荐】
* 直接修改配置文件【不推荐】
## 生效方式
* 第一次启动后不可修改 (first_start)
* 重启后生效 (restart)
* 热加载 (hot_reload)
# 直接修改配置文件
可以通过重启或以下命令生效 
## 热加载配置命令
使支持热加载的配置项改动立即生效。
对于已经写在配置文件中修改过的配置项，从配置文件中删除或注释后再进行 load configuration 将恢复默认值。
```
load configuration
```
# 配置项操作语句
设置配置项
```
set configuration 'key1' = 'value1' 'key2' = 'value2'... (on nodeId)
```
### 示例1
```
set configuration 'enable_cross_space_compaction' = 'false'
```
对集群所有节点永久生效，设置 enable_cross_space_compaction 为 false，并写入到 iotdb-system.properties 中。
### 示例2
```
set configuration 'enable_cross_space_compaction' ='false' 'enable_seq_space_compaction' = 'false' on 1
```
对 nodeId 为 1 的节点永久生效，设置 enable_cross_space_compaction 为 false，设置 enable_seq_space_compaction 为 false，并写入到 iotdb-system.properties 中。
### 示例3
```
set configuration  'enable_cross_space_compaction' = 'false'  'timestamp_precision' = 'ns'
```
对集群所有节点永久生效，设置 enable_cross_space_compaction 为 false，timestamp_precision 为 ns，并写入到 iotdb-system.properties 中。但是，timestamp_precision 是第一次启动后就无法修改的配置项，因此会忽略这个配置项的更新，返回如下。
```
Msg: org.apache.iotdb.jdbc.IoTDBSQLException: 301: ignored config items: [timestamp_precision]
```
# 生效配置项
支持热加载立即生效的配置项在 iotdb-system.properties.template 文件中标记 effectiveMode 为 hot_reload
示例
```
# Used for indicate cluster name and distinguish different cluster.
# If you need to modify the cluster name, it's recommended to use [set configuration 'cluster_name'='xxx'] sql.
# Manually modifying configuration file is not recommended, which may cause node restart fail.
# effectiveMode: hot_reload
# Datatype: string
cluster_name=defaultCluster
```