How to EXPIRE the HSET child key in redis

Question

I need to expire all keys in redis hash  which are older than 1 month

User · Answer

This is possible in KeyDB which is a Fork of Redis. Because it's a Fork its fully compatible with Redis and works as a drop in replacement.

Just use the EXPIREMEMBER command. It works with sets, hashes, and sorted sets.

EXPIREMEMBER keyname subkey [time]

You can also use TTL and PTTL to see the expiration

TTL keyname subkey

More documentation is available here: https://docs.keydb.dev/docs/commands/#expiremember

User · Answer

We had the same problem discussed here   We have a Redis hash  a key to hash entries  name value pairs   and we needed to hold individual expiration times on each hash entry   We implemented this by adding n bytes of prefix data containing encoded expiration information when we write the hash entry values  we also set the key to expire at the time contained in the value being written   Then  on read  we decode the prefix and check for expiration  This is additional overhead  however  the reads are still O n  and the entire key will expire when the last hash entry has expired

User · Answer

You can  Here is an example   redis 127 0 0 1 6379 gt  hset key f1 1  integer  1 redis 127 0 0 1 6379 gt  hset key f2 2  integer  1 redis 127 0 0 1 6379 gt  hvals key 1   1  2   1  3   2  redis 127 0 0 1 6379 gt  expire key 10  integer  1 redis 127 0 0 1 6379 gt  hvals key 1   1  2   1  3   2  redis 127 0 0 1 6379 gt  hvals key 1   1  2   1  3   2  redis 127 0 0 1 6379 gt  hvals key   Use EXPIRE or EXPIREAT command   If you want to expire specific keys in the hash older then 1 month  This is not possible  Redis expire command is for all keys in the hash  If you set daily hash key  you can set a keys time to live   hset key-20140325 f1 1 expire key-20140325 100 hset key-20140325 f1 2

User · Answer

You can use Sorted Set in redis to get a TTL container with timestamp as score   For example  whenever you insert a event string into the set you can set its score to the event time   Thus you can get data of any time window by calling  zrangebyscore  your set name  min-time max-time  Moreover  we can do expire by using zremrangebyscore  your set name  min-time max-time to  remove old events   The only drawback here is you have to do housekeeping from an outsider process to maintain the size of the set

User · Answer

There is a Redisson java framework which implements hash Map object with entry TTL support  It uses hmap and zset Redis objects under the hood  Usage example   RMapCache lt Integer  String gt  map   redisson getMapCache  map    map put 1  30  TimeUnit DAYS      this entry expires in 30 days   This approach is quite useful

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Regarding a NodeJS implementation  I have added a custom expiryTime field in the object I save in the HASH  Then after a specific period time  I clear the expired HASH entries by using the following code   client hgetall HASH NAME  function err  reply        if  reply            Object keys reply  forEach key   gt                if  reply key   amp  amp  JSON parse reply key   expiryTime  lt   new Date  getTime                      client hdel HASH NAME  key

User · Answer

You could store key values in Redis differently to achieve this  by just adding a prefix or namespace to your keys when you store them e g   hset     Get a key value GET hset key equals to HGET hset key  Add a key value SET hset key value equals to HSET hset key Get all keys KEYS hset   equals to HGETALL hset  Get all vals should be done in 2 ops  first get all keys KEYS hset   then get the value for each key  Add a key value with TTL or expire which is the topic of question     SET hset key value  EXPIRE hset key   Note  KEYS will lookup up for matching the key in the whole database which may affect on performance especially if you have big database    Note     KEYS will lookup up for matching the key in the whole database which may affect on performance especially if you have big database  while SCAN 0 MATCH hset   might be better as long as it doesn t block the server but still performance is an issue in case of big database   You may create a new database for storing separately these keys that you want to expire especially if they are small set of keys       Thanks to  DanFarrell who highlighted the performance issue related to   KEYS

User · Answer

Redis does not support having TTL on hashes other than the top key  which would expire the whole hash  If you are using a sharded cluster  there is another approach you could use  This approach could not be useful in all scenarios and the performance characteristics might differ from the expected ones  Still worth mentioning   When having a hash  the structure basically looks like   hash top key   - child key 1 - gt  some value   - child key 2 - gt  some value         - child key n - gt  some value   Since we want to add TTL to the child keys  we can move them to top keys  The main point is that the key now should be a combination of hash top key and child key    hash top key child key 1 - gt  some value  hash top key child key 2 - gt  some value      hash top key child key n - gt  some value   We are using the    notation on purpose  This allows all those keys to fall in the same hash slot  You can read more about it here  https   redis io topics cluster-tutorial  Now if we want to do the same operation of hashes  we could do   HDEL hash top key child key 1   gt  DEL  hash top key child key 1  HGET hash top key child key 1   gt  GET  hash top key child key 1  HSET hash top key child key 1 some value   gt  SET  hash top key child key 1 some value  some TTL   HGETALL hash top key   gt     keyslot   CLUSTER KEYSLOT  hash top key    keys   CLUSTER GETKEYSINSLOT keyslot n   MGET keys   The interesting one here is HGETALL  First we get the hash slot for all our children keys  Then we get the keys for that particular hash slot and finally we retrieve the values  We need to be careful here since there could be more than n keys for that hash slot and also there could be keys that we are not interested in but they have the same hash slot  We could actually write a Lua script to do those steps in the server by executing an EVAL or EVALSHA command  Again  you need to take into consideration the performance of this approach for your particular scenario   Some more references    https   redis io commands cluster-keyslot https   redis io commands cluster-getkeysinslot https   redis io commands eval

User · Answer

If your use-case is that you re caching values in Redis and are tolerant of stale values but would like to refresh them occasionally so that they don t get too stale  a hacky workaround is to just include a timestamp in the field value and handle expirations in whatever place you re accessing the value  This allows you to keep using Redis hashes normally without needing to worry about any complications that might arise from the other approaches  The only cost is a bit of extra logic and parsing on the client end  Not a perfect solution  but it s what I typically do as I haven t needed TTL for any other reason and I m usually needing to do extra parsing on the cached value anyways  So basically it ll be something like this  In Redis  hash name - field 1   quot 2021-01-15 123 quot  - field 2   quot 2021-01-20 125 quot  - field 2   quot 2021-02-01 127 quot   Your  pseudo code  val   redis hget hash name  field 1  timestamp   val substring 0  val index of  quot   quot     if now    gt  timestamp    new val   get updated value     new timestamp   now     EXPIRY LENGTH   redis hset hash name  field 1  new timestamp    quot   quot    new val    val   new val else    val   val substring val index of  quot   quot        proceed to use val  The biggest caveat imo is that you don t ever remove fields so the hash can grow quite large  Not sure there s an elegant solution for that - I usually just delete the hash every once in a while if it feels too big  Maybe you could keep track of everything you ve stored somewhere and remove them periodically  though at that point  you might as well just be using that mechanism to expire the fields manually

User · Answer

This is not possible  for the sake of keeping Redis simple   Quoth Antirez  creator of Redis      Hi  it is not possible  either use a different top-level key for that   specific field  or store along with the filed another field with an   expire time  fetch both  and let the application understand if it is   still valid or not based on current time

User · Answer

You could use the Redis Keyspace Notifications by using psubscribe and    keyevent  lt DB-INDEX gt    expired     With that  each time that a key will expire  you will get a message published on your redis connection     Regarding your question basically you create a temporary  normal  key using set with an expiration time in s ms  It should match the name of the key that you wish to delete in your set    As your temporary key will be published to your redis connection holding the    keyevent 0   expired  when it expired  you can easily delete your key from your original set as the message will have the name of the key    A simple example in practice on that page   https   medium com  micah1powell using-redis-keyspace-notifications-for-a-reminder-service-with-node-c05047befec3  doc   https   redis io topics notifications   look for the flag xE

User · Answer

You can expire Redis hashes in ease   Eg using python  import redis conn   redis Redis  localhost   conn hmset  hashed user     name    robert    age   32   conn expire  hashed user   10    This will expire all child keys in hash hashed user after 10 seconds  same from redis-cli   127 0 0 1 6379 gt  HMSET testt username wlc password P1pp0 age 34 OK 127 0 0 1 6379 gt  hgetall testt 1   username  2   wlc  3   password  4   P1pp0  5   age  6   34  127 0 0 1 6379 gt  expire testt 10  integer  1 127 0 0 1 6379 gt  hgetall testt 1   username  2   wlc  3   password  4   P1pp0  5   age  6   34    after 10 seconds  127 0 0 1 6379 gt  hgetall testt  empty list or set

[hash] How to "EXPIRE" the "HSET" child key in redis?

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