Decrementing Values in Memcached with Java (Detailed Guide w/ Code Examples)
The decr function is used when you need to decrement a numeric value stored in Memcached. This is often utilized in scenarios like:
Tracking available inventory of an item
Counting down from a specific number, like during a countdown
Rate limiting where you increment a counter each time a user accesses a service and decrement it after a certain period
Let's assume that we have a system that tracks the remaining seats for a concert. Here is how you could set up and use decr.
// Assuming you have already established a connection to Memcached named 'memcachedClient'String key ="remaining_seats";int initialValue =100;int expiryTime =3600;// Setting the expiry time for 1 hour// Set initial value in memcachedmemcachedClient.set(key, expiryTime, initialValue);// Now lets decrement the value by 1long newValue = memcachedClient.decr(key,1);System.out.println("New Value: "+ newValue);// Output: New Value: 99
This will reduce the value of 'remaining_seats' key in Memcached by 1.
Always check if the key exists before trying to decrement its value. If the key doesn't exist, Memcached will return 0.
Be aware of underflows. Memcached won't allow the value to go below 0, so if you decrement a value that's currently at 0, the operation will fail.
When decrementing, make sure the stored value is a numeric string. Other types may lead to unpredictable results.
Trying to decrement non-numeric values. Memcached decr function works only on numeric values. If the value is non-numeric, you'll get an error.
Not handling missing keys. If a key does not exist, Memcached will return 0 and will not create this key.
Q: What happens if the new value should be less than zero?
A: Memcached will not let the value go below 0. If a decrement operation would result in a negative number, the new value will instead be 0.
Q: What will happen if I try to decrement a key that does not exist?
A: If a key does not exist in Memcached and you try to decrement it, Memcached will simply return 0.