Use time-to-live (TTL) to expire data in a column or table.
Columns and tables support an optional expiration period called TTL (time-to-live); TTL is not supported on counter columns. Define the TTL value in seconds. Data expires once it exceeds the TTL period and is then marked with a tombstone. Expired data continues to be available for read requests during the grace period, see gc_grace_seconds. Normal compaction and repair processes automatically remove the tombstone data.
- TTL precision is one second, which is calculated by the coordinator node. When using TTL, ensure that all nodes in the cluster have synchronized clocks.
A very short TTL is not very useful.
Expiring data uses additional 8 bytes of memory and disk space to record the TTL and grace period.
Setting a TTL for a specific column
Use CQL to set the TTL.
To change the TTL of a specific column, you must re-insert the data with a new TTL. Cassandra upserts the column with the new TTL.
To remove TTL from a column, set TTL to zero. For details, see the UPDATE documentation.
Setting a TTL for a table
For details and examples, see Expiring data with TTL example.