• antirez's avatar
    Track number of logically expired keys still in memory. · ffde73c5
    antirez authored
    This commit adds two new fields in the INFO output, stats section:
    
    expired_stale_perc:0.34
    expired_time_cap_reached_count:58
    
    The first field is an estimate of the number of keys that are yet in
    memory but are already logically expired. They reason why those keys are
    yet not reclaimed is because the active expire cycle can't spend more
    time on the process of reclaiming the keys, and at the same time nobody
    is accessing such keys. However as the active expire cycle runs, while
    it will eventually have to return to the caller, because of time limit
    or because there are less than 25% of keys logically expired in each
    given database, it collects the stats in order to populate this INFO
    field.
    
    Note that expired_stale_perc is a running average, where the current
    sample accounts for 5% and the history for 95%, so you'll see it
    changing smoothly over time.
    
    The other field, expired_time_cap_reached_count, counts the number
    of times the expire cycle had to stop, even if still it was finding a
    sizeable number of keys yet to expire, because of the time limit.
    This allows people handling operations to understand if the Redis
    server, during mass-expiration events, is able to collect keys fast
    enough usually. It is normal for this field to increment during mass
    expires, but normally it should very rarely increment. When instead it
    constantly increments, it means that the current workloads is using
    a very important percentage of CPU time to expire keys.
    
    This feature was created thanks to the hints of Rashmi Ramesh and
    Bart Robinson from Twitter. In private email exchanges, they noted how
    it was important to improve the observability of this parameter in the
    Redis server. Actually in big deployments, the amount of keys that are
    yet to expire in each server, even if they are logically expired, may
    account for a very big amount of wasted memory.
    ffde73c5
server.c 152 KB