Records with ttl set never have their expiration time shortened

1

I saw the following sentence on the cold start page. “Records with ttl set never have their expiration time shortened.”, What does that mean, please?

2

I believe the sentence appears on this page that describes the behavior during a cold restart. It simply means the record’s ttl was never modified to a smaller value. The significance of a record’s ttl ever being shortened is that there is a possibility of the older, longer ttl version on the disk, reappearing although it has been superseded by a shorter ttl version if that version expired but was not written to disk. If a record’s ttl was never shortened, an older version will not be resurrected during cold restart.

For a more detailed discussion, you can read this article.

3

Thank for your excellent answer. Does this mean that if I use TTL to create a record, but then update it with a smaller TTL:

  • Record created with ttl1 (gen-1 / ttl1 - void time t1)

  • Record updated with ttl2 (gen-2 / ttl2 - void time t2 < t1)

  • Record expires

    public static void main(String[] args) {
        // save to aerospike , set ttl to 30s
        saveWithExpiration(30);

        // update record ttl, set ttl to 1s
        saveWithExpiration(1);
    }

    private static void saveWithExpiration(int expire) {
        WritePolicy writePolicy = new WritePolicy();
        writePolicy.expiration = expire;
        Key key = new Key(NAMESPACE, SET_NAME, KEY_NAME);
        Bin bin = new Bin(BIN_NAME, "expire time " + expire);
        aerospikeClient.put(writePolicy, key, bin);
    }

The records with Gen-2 may not be written to disk due to the reason that the defragmentation is overwritten, so I will bring back the records with gen-1 when I cold start aerospike.

4

The example is correct. Note you may only change the expiration time without bin updates using “touch” operation. A general statement is that if a record’s ttl is ever shortened (set to an earlier expiration time), an older version with farther out expiration may be resurrected during cold restart.