Cassandra - defining a global TTL and changing an already existing one

Question

I know that one can define a TTL when making an INSERT / UPDATE to a Cassandra column / table etc. (INSERT INTO ... USING TTL 1234). One can also define a default TTL when creating a table (CREATE TABLE ... WITH default_time_to_live="1234";).

However is it possible to define defaults that are more global? Possible scenarios would include:

• Defining a global TTL when creating a keyspace (so that any tables inherit the TTL)? Judging by the docs it seems that it's not supported (https://docs.datastax.com/en/dse/5.1/cql/cql/cql_reference/cql_commands/cqlCreateKeyspace.html & https://docs.datastax.com/en/dse/5.1/cql/cql/cql_using/useExpire.html), but thought it's worth asking just in case
• Defining (in the cassandra.yaml config?) a global TTL for any new keyspaces
• Defining a global TTL for any new data in the whole cluster

The other question would be:

• Is there is a quick and cheap way to change (increase, decrease) TTL for an already-existing data (as globally as possible - hopefully table level)? According to the docs a re-insert is required (https://docs.datastax.com/en/dse/5.1/cql/cql/cql_using/useExpire.html#useExpire__setting-a-ttl-for-a-specific-column-RYjSo4Iu), so a simple ALTER TABLE will not work. Is it right? Can anyone suggest some better ideas?

Answer 1

Your kind of answered your own question. 1. TTL is only possible at column or at Table level. 2. To alter the TTL of an existing column you need to reinsert it with the new value.

You can set the TTL at table level with the create table ddl and with the table property default_time_to_live.

When you rewrite the column it will Upsert it with the new TTL. there wont be two rows lying. Remember every DML goes into cassandra with a timestamp and the latest update wins.