Redis Key Expiration

Expiry of key

• Set expiry In seconds
  • EX <seconds>
• Set expiry In Milliseconds
  • PX <milliseconds>
• Check Time To live in seconds
  • ttl <keyname>
• Check Time To live in milliseconds
  • pttl <keyname>
• -1 return from ttl says that key is never gonna expire
• -2 return from ttl says that key does not exist
• Explicity set an expiry for an key / Change an expiry of a existing key
  • expire <key> <seconds>
  • pexpire <key> <milliseconds>
• Remove expiry
  • persist <keyname>

Setting Expiry in seconds

Setting Expiry in milliseconds

Changing the expiry of thekey

Persisting an expiry of key

How does Redis Handle Key Expiration

There are two ways in which redis handles key expiration

• Passive
  • When the key is called, it is checks/compared with the keys time to live to the current time
  • It the time is past time to expire then it removes the key from redis cache and returns -2 (-2 i.e key does not exist)
• Active
  • Active key expiration runs 10 times per second
  • Redis test 20 random keys from the set of keys with an associated expiry
  • This deletes all the keys that are expired
  • If more than 25% keys are expired then it will start again from step 1