docs/cql/time-to-live.rst
.. highlight:: cql
.. _time-to-live:
ScyllaDB (as well as Apache Cassandra) provides the functionality to automatically delete expired data according to the Time to Live (or TTL) value. TTL is measured in seconds. If the field is not updated within the TTL it is deleted. The TTL can be set when defining a Table (CREATE), or when using the INSERT and UPDATE queries. The expiration works at the individual column level, which provides a lot of flexibility. By default, the TTL value is null, which means that the data will not expire.
This document is about CQL's classic per-write TTL feature, where individual
columns from the same row can expire at separate times if written at
different times. ScyllaDB also supports an alternative TTL feature,
Per-row TTL <https://docs.scylladb.com/stable/cql/cql-extensions.html#per-row-ttl>_.
In per-row TTL each row has an expiration time for the entire row,
defined by the value of the expiration-time column. In per-row TTL, the
entire row expires together regardless of how its indivial columns were
written, and the expiration time of an entire row can be modified by modifying
the expiration-time column. Another benefit of per-row TTL is that it
generates a CDC event when a row expires - in contrast in per-write TTL
(the feature described in this document) where expiration events do not
show up in CDC.
.. note::
The expiration time is always calculated as now() on the Coordinator + TTL where, now() is the wall clock during the corresponding write operation. In particular, it means that a value given via USING TIMESTAMP is not taken into an account for an expiration calculation.
TTL using UPDATE and INSERT ^^^^^^^^^^^^^^^^^^^^^^^^^^^
To set the TTL value using the UPDATE query use the following command:
.. code-block:: cql
UPDATE heartrate USING TTL 600 SET heart_rate =
110 WHERE pet_chip_id = 123e4567-e89b-12d3-a456-426655440b23;
In this case, the TTL for the heart_rate column is set 10 minutes (600 seconds).
To check the TTL, use the TTL() function:
.. code-block:: cql
SELECT name, heart_rate, TTL(heart_rate)
FROM heartrate WHERE pet_chip_id = 123e4567-e89b-12d3-a456-426655440b23;
The TTL has a value that is lower than 600 as a few seconds passed between setting the TTL and the SELECT query. If you wait 10 minutes and run this command again, you will get a null value for the heart_rate.
It’s also possible to set the TTL when performing an INSERT. To do this use:
.. code-block:: cql
INSERT INTO heartrate(pet_chip_id, name, heart_rate) VALUES (c63e71f0-936e-11ea-bb37-0242ac130002, 'Rocky', 87) USING TTL 30;
In this case, a TTL of 30 seconds is set.
TTL for a Table ^^^^^^^^^^^^^^^ Use the CREATE TABLE or ALTER TABLE commands and set the default_time_to_live value:
.. code-block:: cql
CREATE TABLE heartrate_ttl (
pet_chip_id uuid,
name text,
heart_rate int,
PRIMARY KEY (pet_chip_id))
WITH default_time_to_live = 600;
Here a TTL of 10 minutes is applied to all rows, however, keep in mind that TTL is stored on a per column level for non-primary key columns.
It’s also possible to change the default_time_to_live on an existing table using the ALTER command:
.. code-block:: cql
ALTER TABLE heartrate_ttl WITH default_time_to_live = 3600;
TTL with LWT .............
.. include:: /rst_include/note-ttl-lwt.rst
Refer to :doc:LWT </features/lwt/> for more information.
The gc_grace_seconds parameter is defined :ref:here <create-table-general-options>.
TTL for a Collection ^^^^^^^^^^^^^^^^^^^^
You can set the TTL on a per element basis for collections. An example of how to do this, is shown in the :ref:Maps <maps> CQL Reference.
Notes ^^^^^
Additional Information ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
To learn more about TTL, and see a hands-on example, check out this lesson <https://university.scylladb.com/courses/data-modeling/lessons/advanced-data-modeling/topic/expiring-data-with-ttl-time-to-live/>_ on ScyllaDB University.
Video: Managing data expiration with Time-To-Live <https://www.youtube.com/watch?v=SXkbu7mFHeA>_Apache Cassandra Query Language (CQL) Reference </cql/index>KB Article:How to Change gc_grace_seconds for a Table </kb/gc-grace-seconds/>KB Article:Time to Live (TTL) and Compaction </kb/ttl-facts/>CQL Reference: Table Options <create-table-general-options>