SpaceTL 删除

1. 概述

IoTDB 支持通过参数配置 SpaceTL 删除策略：即当最后一级存储层（对象存储空间被视为无限）的存储空间不足时，可选择是否触发 SpaceTL 删除机制以释放空间。

注意：该机制仅会删除最后一个存储层中的文件。

2. 参数介绍

参数名	描述	默认值	生效方式
dn_tier_full_policy	最后一级存储层存储空间不足时的行为策略。可配置：1. NULL：不做任何处理1. DELETE：开启 SpaceTL 删除数据。	NULL	热加载

参数说明：

若最后一级存储层包含对象存储则不触发 SpaceTL
该参数和 dn_default_space_usage_thresholds 参数联动，当最后一级存储层的可用空间低于 space_usage_thresholds 时触发 SpaceTL；默认当磁盘空间占用到达 85% 的时候开始删除直至空间占用降到 85% 以下才会停止

3. 使用示例

以三级存储为例，当最后一级存储空间到达85%时，触发 SpaceTL 删除机制开始删除文件。

# data dirs
# If this property is unset, system will save the data in the default relative path directory under the IoTDB folder(i.e., %IOTDB_HOME%/data/datanode/data).
# If it is absolute, system will save the data in exact location it points to.
# If it is relative, system will save the data in the relative path directory it indicates under the IoTDB folder.
# If there are more than one directory, please separate them by commas ",".
# If tiered storage is enabled, please separate directories of different tiers by semicolons ";".
# Use keyword OBJECT_STORAGE to denote object storage media, object storage can only exist on the last tier and must have local dirs in the front tiers.
# Note: If data_dirs is assigned an empty string(i.e.,zero-size), it will be handled as a relative path.
# effectiveMode: hot_reload
# For windows platform
# If its prefix is a drive specifier followed by "\\", or if its prefix is "\\\\", then the path is absolute. Otherwise, it is relative.
# dn_data_dirs=data\\datanode\\data
# For Linux platform
# If its prefix is "/", then the path is absolute. Otherwise, it is relative.
dn_data_dirs=/data1/data;/data2/data,/data3/data;/data4/data

# Default tier TTL. When the survival time of the data exceeds the threshold, it will be migrated to the next tier.
# Negative value means the tier TTL is unlimited.
# effectiveMode: restart
# Datatype: long
# Unit: ms
tier_ttl_in_ms=86400000;864000000;-1

# Disk usage threshold, data will be moved to the next tier when the usage of the tier is higher than this threshold.
# If tiered storage is enabled, please separate thresholds of different tiers by semicolons ";".
# effectiveMode: hot_reload
# Datatype: double(percentage)
dn_default_space_usage_thresholds=0.75;0.8;0.85

# How to deal with the last tier?s data when its used space has been higher than its dn_default_space_usage_thresholds.
# The info of the two policies are as follows:
# effectiveMode: hot_reload
# 1. NULL: do nothing.
# 2. DELETE: delete the oldest data.
dn_tier_full_policy=DELETE

在该示例中，共配置了三个层级的存储，具体为：

层级	存储目录	数据保留时间	磁盘存储空间阈值
层级一	/data1/data	只保留 1 天，超过后会移动到第二级	磁盘达到 75% 会移动部分文件到第二级
层级二	/data2/data,/data3/data	只保留 10 天，超过后到第三级	磁盘达到 80% 会移动部分文件到第三级
层级三	/data4/data	没有过期时间，会一直存储	磁盘达到 85% 会删除部分文件（因为dn_tier_full_policy=DELETE）