Java Memcached Flush All (Detailed Guide w/ Code Examples)

Use Case(s)

When working with Memcached in a Java environment, it's often necessary to purge all data from the cache. This might be needed during application testing when you want to ensure a clean state for each test, or in production when you've updated a large number of records and need to ensure the cache is in sync.

Code Examples

Using net.spy.memcached

Here's an example using the widely-used net.spy.memcached library:

import net.spy.memcached.MemcachedClient;

MemcachedClient c=new MemcachedClient(new InetSocketAddress("localhost", 11211));

// flush all items in cache
c.flush();

This will delete all items from your Memcached instance. The flush operation is asynchronous in nature, so changes may not reflect immediately.

Using xmemcached

Here's another example using the xmemcached library, which provides more detailed control over the Memcached server:

import com.googlecode.xmemcached.MemcachedClient;
import com.googlecode.xmemcached.XMemcachedClient;

MemcachedClient c = new XMemcachedClient("localhost", 11211);

// flush all items in cache
c.flushAll();

The flushAll() method in xmemcached works similar to the flush() method in net.spy.memcached, flushing all items from the cache.

Best Practices

When using flush or flushAll, remember these operations are powerful and will clear all keys from your cache irrespective of namespaces or other organizational units within the cache. Be sure to use them judiciously in order to avoid causing unnecessary load on your database servers by causing a sudden surge in cache misses.

Common Mistakes

Not understanding the asynchronous nature of flush operations can lead to issues. The operation returns immediately while the actual deletion happens in the background. Trying to read or write data immediately after a flush call may lead to unexpected results.

FAQs

Q: Is it bad to use Memcached's 'flush' too often?

A: Yes, flushing your cache frequently can defeat the purpose of having a cache by causing a sudden increase in cache misses and potentially overloading your database servers.

Q: Can I undo a flush operation?

A: No, once a flush operation has been initiated, it can't be undone. The only way to repopulate the cache is through normal application usage.