There is a post about a Redis command to get all available keys, but I would like to do it with Python.
Any way to do this?
Use scan_iter()
scan_iter() is superior to keys() for large numbers of keys because it gives you an iterator you can use rather than trying to load all the keys into memory.
I had a 1B records in my redis and I could never get enough memory to return all the keys at once.
SCANNING KEYS ONE-BY-ONE
Here is a python snippet using scan_iter() to get all keys from the store matching a pattern and delete them one-by-one:
import redis
r = redis.StrictRedis(host='localhost', port=6379, db=0)
for key in r.scan_iter("user:*"):
# delete the key
r.delete(key)
SCANNING IN BATCHES
If you have a very large list of keys to scan - for example, larger than >100k keys - it will be more efficient to scan them in batches, like this:
import redis
from itertools import izip_longest
r = redis.StrictRedis(host='localhost', port=6379, db=0)
# iterate a list in batches of size n
def batcher(iterable, n):
args = [iter(iterable)] * n
return izip_longest(*args)
# in batches of 500 delete keys matching user:*
for keybatch in batcher(r.scan_iter('user:*'),500):
r.delete(*keybatch)
I benchmarked this script and found that using a batch size of 500 was 5 times faster than scanning keys one-by-one. I tested different batch sizes (3,50,500,1000,5000) and found that a batch size of 500 seems to be optimal.
Note that whether you use the scan_iter() or keys() method, the operation is not atomic and could fail part way through.
DEFINITELY AVOID USING XARGS ON THE COMMAND-LINE
I do not recommend this example I found repeated elsewhere. It will fail for unicode keys and is incredibly slow for even moderate numbers of keys:
redis-cli --raw keys "user:*"| xargs redis-cli del
In this example xargs creates a new redis-cli process for every key! that's bad.
I benchmarked this approach to be 4 times slower than the first python example where it deleted every key one-by-one and 20 times slower than deleting in batches of 500.