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Using Java, can I scan a Cassandra table and just update the TTL of a row? I don't want to change any data. I just want to scan Cassandra table and set TTL of a few rows.

Also, using java, can I set TTL which is absolute. for example (2016-11-22 00:00:00). so I don't want to specify the TTL in seconds, but specify the absolute value in time.

Knows Not Much
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3 Answers3

27

Cassandra doesn't allow to set the TTL value for a row, it allows to set TTLs for columns values only.

In the case you're wondering why you are experiencing rows expiration, this is because if all the values of all the columns of a record are TTLed then the row disappears when you try to SELECT it.

However, this is only true if you perform an INSERT with the USING TTL. If you INSERT without TTL and then do an UPDATE with TTL you'll still see the row, but with null values. Here's a few examples and some gotchas:

Example with a TTLed INSERT only:

CREATE TABLE test (
    k text PRIMARY KEY,
    v int,
);

INSERT INTO test (k,v) VALUES ('test', 1) USING TTL 10;

... 10 seconds after...

SELECT * FROM test ;

 k             | v
---------------+---------------

Example with a TTLed INSERT and a TTLed UPDATE:

INSERT INTO test (k,v) VALUES ('test', 1) USING TTL 10;
UPDATE test USING TTL 10 SET v=0 WHERE k='test';

... 10 seconds after...

SELECT * FROM test;

 k             | v
---------------+---------------

Example with a non-TTLed INSERT with a TTLed UPDATE

INSERT INTO test (k,v) VALUES ('test', 1);
UPDATE test USING TTL 10 SET v=0 WHERE k='test';

... 10 seconds after...

SELECT * FROM test;

 k             | v
---------------+---------------
          test |          null

Now you can see that the only way to solve you problem is to rewrite all the values of all the columns of your row with a new TTL.

In addition, there's no way to specify an explicit expiration date, but you can get a simple TTL value in seconds with simple math (as other suggested).

Have a look at the official documentation about data expiration. And don't forget to have a look at the DELETE section for updating TTLs.

HTH.

xmas79
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  • I dug into this a bit recently and noted this. The simple answer is `INSERT INTO test (k,v) VALUES ('test', 1) USING TTL 10;` will expire a row. There is a hidden cell that gets created for the key that will get the expiration when inserting. This cell will only have a TTL on `insert` you can't modify this cell manually. So if you reinsert the entire row you can set a TTL on a row. If you set the TTL initially on insert, then update the TTL for a column, this will extend the TTL for the row, but as soon as that TTL expires on that column, the entire row is expired. – HypnoticPancake May 07 '21 at 21:36
3

You can't only update TTL of a row. You have to update or re-insert all the column.

You can select all the regular column and the primary keys column then update the regular columns with primary keys or re-insert using TTL in second

In Java you can calculate TTL in second from a date using below method.

public static long ttlFromDate(Date ttlDate) throws Exception {
    long ttl = (ttlDate.getTime() - System.currentTimeMillis()) / 1000;
    if (ttl < 1) {
        throw new Exception("Invalid ttl date");
    }
    return ttl;
}
Ashraful Islam
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1

Alternatively, you can set a TTL value on the entire table while creating it. 

CREATE TABLE test (
    k text PRIMARY KEY,
    v int,
) WITH default_time_to_live = 63113904;

Above example will create a table whose rows will disappear after 2 years.

bekce
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