Expiring data with time-to-live
Columns and tables support an optional expiration period called TTL (time-to-live).
You define the TTL value in seconds. The data expires once it exceeds the TTL period, and it is then marked with a tombstone.
During the grace period (gc_grace_seconds), expired data is still stored as tombstoned data in the database.
Tombstoned data is scanned by database read operations, but it isn’t included in the returned data.
Normal compaction and repair processes automatically remove the tombstone data.
TTL requirements and limitations
-
TTL is not supported on
countercolumns. -
TTL precision is one second, which is calculated by the coordinator node. When setting a TTL, ensure that all nodes in the cluster have synchronized clocks.
-
A very short TTL is not useful.
-
Expiring data uses additional 8 bytes of memory and disk space to record the TTL and grace period.
|
The database storage engine can only encode TTL timestamps through The TTL date overflow policy ( |
Set a TTL for a specific column
The USING TTL clause can be used to set the TTL when you insert or update data.
For more information and examples, see Set the time-to-live (TTL).
To change the TTL of a specific column, you must re-insert the data with a new TTL. The column is upserted with the new TTL.
To remove the TTL from a column, set the TTL to zero.
For details, see UPDATE.
Set a TTL for a table
Use CREATE TABLE or ALTER TABLE to define the default_time_to_live property for all columns in a table.
If any column exceeds the TTL, then the entire row is deleted.
Setting TTL on a column using the INSERT or UPDATE command overrides the table-level TTL.
