The incr
operation in Memcached is widely used when we need to increment a numeric value stored in the cache. It's often useful in rate limiting, counters, and other scenarios where atomic increments are needed.
Let's consider two examples using the incr
method with spymemcached, a popular memcached client for Java.
incr
to increment it.MemcachedClient c=new MemcachedClient(new InetSocketAddress("localhost", 11211)); // Set initial value c.set("counter", 3600, 0); // Increment counter c.incr("counter", 1);
In this example, we first initialize a counter named 'counter' to 0 with an expiry time of 1 hour (3600 seconds). Then, we increment the value by 1 each time the incr
function is called.
incr
can be used to limit the number of requests made by a user.MemcachedClient c=new MemcachedClient(new InetSocketAddress("localhost", 11211)); String userID = "user123"; String key = userID + "_requests"; // Increment the request count long requests = c.incr(key, 1, 1, 60); // expire after 60 seconds if (requests > 10) { System.out.println("Rate limit exceeded"); }
In this example, we keep track of the number of requests made by a user within a minute. If a user makes more than 10 requests, we print a message indicating that the rate limit has been exceeded.
incr
or decr
operations, as they only work with numeric values.incr
operation won't work if the key doesn't exist or isn't a number. Always make sure to initialize your counter keys with a numeric value using the set
operation before incrementing or decrementing them.incr
and decr
commands help mitigate this issue.Does Memcached's incr
operation guarantee atomicity?
Yes, Memcached guarantees atomic increments, which means multiple clients can safely increment the same key simultaneously without causing a race condition.
What happens when the incremented value exceeds the maximum size of an integer?
Memcached stores values as unsigned 64-bit integers. If a value incremented by incr
exceeds this range, it wraps around to 0.
Dragonfly is fully compatible with the Redis ecosystem and requires no code changes to implement.