IoTDB supports configuring the SpaceTL deletion policy through parameters: when the storage space of the last-level storage tier (object storage space is considered unlimited) is insufficient, users can choose whether to trigger the SpaceTL deletion mechanism to free up space.
Note: This mechanism only deletes files in the last storage tier.
| Parameter Name | Description | Default Value | Effective Mode |
|---|---|---|---|
dn_tier_full_policy | Behavior policy when the storage space of the last-level storage tier is insufficient. Configurable options:1. NULL: Take no action.2. DELETE: Enable SpaceTL data deletion. | NULL | Hot Reload |
Parameter Explanation:
dn_default_space_usage_thresholdsparameter. SpaceTL is triggered when the available space of the last-level storage tier falls below the space_usage_thresholds. By default, deletion begins when disk space usage reaches 85% and continues until usage drops below 85%.In a three-tier storage setup, when the storage space of the last tier reaches 85%, the SpaceTL deletion mechanism is triggered to start deleting files.
# 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
In this example, three tiers of storage are configured as follows:
| Tier Level | Storage Directories | Data Retention Time | Disk Storage Space Threshold |
|---|---|---|---|
| Tier 1 | /data1/data | Retained for 1 day; exceeded data moves to Tier 2 | Data moves to Tier 2 when disk usage reaches 75% |
| Tier 2 | /data2/data,/data3/data | Retained for 10 days; exceeded data moves to Tier 3 | Data moves to Tier 3 when disk usage reaches 80% |
| Tier 3 | /data4/data | No expiration time; data is stored indefinitely | Deletes some files when disk usage reaches 85% (due todn_tier_full_policy=DELETE) |