Limit list length in redis

After every lpush, call ltrim to trim the list to 10 elements

See http://redis.io/commands/ltrim


The following code,

  • pushes the item to the list,
  • keep the size fixed to 10,
  • and returns the most recent 10 elements

in a transaction.

MULTI
LPUSH list "item1"
LTRIM list 0 9
LRANGE list 0 9
EXEC

You can use LTRIM intermittently after any LPUSH, no need to call LTRIM after every LPUSH as that would add to overall latency in your app ( though redis is really fast, but you can save lots of LPUSH operations )

Here is a pseudo code to achieve an LTRIM on approximately every 5th LPUSH:

LPUSH mylist 1
random_int = some random number between 1-5
if random_int == 1:  # trim my list with 1/5 chance
   LTRIM mylist 0 10

Though your list may grow to be a few elements more than 10 elements at times, but it will surely get truncated at regular intervals. This approach is good for most practical purposes and saves a lot of LTRIM operations, keeping your pushes fast.

Tags:

Database

Redis

Recent Posts