CODEWITHSUNDEEP
cassandra
avinash
avinash

Reputation: 49

cassandra TTL for table behaviour

Suppose I inserted a column at second-1 and another column at second-2. Default TTL for table is set to 10 seconds for example:

Question 1: Is data1 and data2 going to be deleted after 10 seconds or data 1 will be deleted after 10 seconds and data-2 after 11 seconds ( as it was inserted in second-2)?

Question 2: Is it possible to set a TTL at a table level in such a way that each entry in the table will expire based on the TTL in a FIFO fashion ? (data-1 will expire at second-10 and data-2 at second-11), without specifying TTL while inserting for each data point? (Should be able to specify at a table level ?)

Thanks for the help :)

EDIT:

the page at https://docs.datastax.com/en/cql/3.1/cql/cql_using/use_expire_c.html says

Setting a TTL for a table

The CQL table definition supports the default_time_to_live property, which applies a specific TTL to each column in the table. After the default_time_to_live TTL value has been exceed, Cassandra tombstones the entire table. Apply this default TTL to a table in CQL using CREATE TABLE or ALTER TABLE

they say "entire table" which confused me.

Upvotes: 4

Views: 4090

Answers (3)

Donz
Donz

Reputation: 1397

I read this topic and a lot of anothers but I'm still confused because at https://docs.datastax.com/en/cql-oss/3.3/cql/cql_using/useExpire.html

they say exactly this:

If any column exceeds TTL, the entire table is tombstoned.

What do they mean? I understand that there is no any sence to tombstone all columns in table when only one exceeded default_time_to_live but they wrote exactly this!

UPD: I did several tests. default_time_to_live means just default TTL on column level. When this TTL expires just concrete columns with expired TTL are tombstoned.

They used very strange sentence in that article.

Upvotes: 0

xmas79
xmas79

Reputation: 5180

TTL at table level is by no means different than TTL at values level: it specifies the default TTL time for each row.

The TTL specifies after how many seconds the values must be considered outdated and thus deleted. The reference point is the INSERT/UPDATE timestamp, so if you insert/update a row at 09:53:01:

  • with a TTL of 10 seconds, it will expire at 09:53:11
  • with a TTL of 15 seconds, it will expire at 09:53:16
  • with a TTL of 0 seconds, it will never expire

You can override the default TTL time by specifying USING TTL X clause in your queries, where X is your new TTl value.

Please note that using TTL not wisely can cause tombstones problems. And note also that the TTL usage have some quirks. Have a look at this recent answer for further details.

Upvotes: 3

Ashraful Islam
Ashraful Islam

Reputation: 12830

Question 1 Ans : data1 will deleted after 10 and data2 will deleted after 11 seconds

Question 2 Ans : Cassandra insert every column with the table's ttl, So Every column will expire on insertion time + ttl.

Upvotes: 2

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