Hi there.
I made a Pull Request to fix bug on ActiveSupport::Cache::MemCacheStore#increment
and decrement for initialization of not stored value.
https://github.com/rails/rails/pull/30716
Regarding initialization, the current document says as follows.
# Increment a cached value. This method uses the memcached incr atomic
# operator and can only be used on values written with the :raw option.
# Calling it on a value not stored with :raw will initialize that value
# to zero.
However, I would rather initialize the value with amount for increment and - amount for decrement
as if the not stored value is initialized to 0 prior to the specified operation.
# Before
@data.incr(normalize_key(name, options), amount, options[:expires_in], 0)
@data.decr(normalize_key(name, options), amount, options[:expires_in], 0)
# After
@data.incr(normalize_key(name, options), amount, options[:expires_in], amount)
@data.decr(normalize_key(name, options), amount, options[:expires_in], -amount)
The reason is that we want to implement appropriate lazy initialization.
For example, simple counter with lazy initialization can be written with instance variable as follows.
def increment(amount)
@counter ||= 0
@counter += amount
end
If we implement the above counter with current ActiveSupport::Cache::MemCacheStore, it can be written as follows.
def increment(amount)
result = @cache.increment(amount)
result != 0 ? result : @cache.increment(amount)
end
As you can see, the initialization to 0 inside @cache actually does not help us write lazy initialization.
We should still handle 0 instead of nil. What is worse, if we use increment and decrement concurrently
on the same key, there is no way to calculate the accurate count.
With the proposed feature request the above code can be simplified as follows.
def increment(amount)
@cache.increment(amount)
end
Also, I have found the same specification on incr of Redis.
If the idea is O.K., I will submit another PR or change the current PR to address the issue.
IMHO, as this initialization has been disabled for a long time, it is about time to improve the specification.