Memcached (vii)--common instruction grasping packet analysis

Using the Spymemcached client, the Wireshark catches the packet and sees the memcached command more clearly.

Let's start with a simple demo:

 PackageSPYMC;Importjava.io.IOException;Importjava.net.InetSocketAddress;ImportNet.spy.memcached.CASResponse;ImportNet.spy.memcached.CASValue;Importnet.spy.memcached.MemcachedClient; Public classTESTSPYMC { Public Static voidMain (string[] args)throwsIOException {memcachedclient C=NewMemcachedclient (NewInetsocketaddress ("aliyun.9game.cn", 11211)); C.set ( "ABC", 3600, "Hello"); System.err.println (c.get ( "ABC")); //casvalue<object> vasvalue = c.gets ("abc"); //casresponse resp= C.cas ("abc", Vasvalue.getcas (), "pre"); //System.out.println (Resp.name ()); //resp= C.cas ("abc", Vasvalue.getcas (), "after"); //System.out.println (Resp.name ());C.shutdown (); }}

The result of the grab will see:

set ABC 0 3600 5helloget ABC storedvalue ABC 0 5helloEND

　　The pink represents the request, and the blue represents the response. Spymemcached said in the previous section thatspymemcached is non-blocking . So the get command is sent out before the SET command response is issued.

Then look at the gets and the CAs. Try to do the CAS operation two times:

 PackageSPYMC;Importjava.io.IOException;Importjava.net.InetSocketAddress;ImportNet.spy.memcached.CASResponse;ImportNet.spy.memcached.CASValue;Importnet.spy.memcached.MemcachedClient; Public classTESTSPYMC { Public Static voidMain (string[] args)throwsIOException {memcachedclient C=NewMemcachedclient (NewInetsocketaddress ("aliyun.9game.cn", 11211)); //C.set ("abc", 3600, "Hello"); //System.err.println (C.get ("abc"));Casvalue<Object> Vasvalue =c.gets ("abc" )); Casresponse resp=C.cas ("abc", Vasvalue.getcas (), "Pre");        System.out.println (Resp.name ()); Resp=C.cas ("abc", Vasvalue.getcas (), "after");        System.out.println (Resp.name ());    C.shutdown (); }}

First, the output is:

Okexists

What the clutch sees is:

gets ABC VALUE ABC 0 3 2272929preEND CAS ABC 0 0 3 2272929pre STORED CAS ABC 0 0 5 2272929after EXISTS

Gets and CAs use version number to achieve atomic operation, repeat two CAs, the same version number, the second time is a failure .

Then try to do a set operation between get and sets. Java code:

 Packageegroup.spymctest;Importjava.io.IOException;Importjava.net.InetSocketAddress;ImportNet.spy.memcached.CASResponse;ImportNet.spy.memcached.CASValue;Importnet.spy.memcached.MemcachedClient; Public classTESTSPYMC { Public Static voidMain (string[] args)throwsIOException {memcachedclient C=NewMemcachedclient (NewInetsocketaddress ("aliyun.9game.cn", 11211));Casvalue<Object> Vasvalue =c.gets ("abc" )); C.set ( "ABC", 3600, "Hello SB"); Casresponse resp=C.cas ("abc", Vasvalue.getcas (), "Pre"); System.out.println (Resp.name ());C.shutdown (); }}

IDE Console output:

EXISTS

The grab bag concludes:

gets ABC VALUE ABC 0 8 2279149hello sbend set ABC 0 3600 8hello sbcas ABC 0 0 3 2279149pre storedexists

When set succeeds, CAS fails.

Visible, Gets&cas, is the concept of optimistic locking. Are not ' exclusive ' data.

Finally, try repeating the add operation. Java code:

        C.add ("Addtest", 3600, "Hello");                C.add ("Addtest", 3600, "Hello");

The grab bag concludes:

Add addtest 0 3600 5helloadd addtest 0 3600 5hello STOREDnot_stored 

The add command of the MC, if there is a key exists, the subsequent add operation will fail . A single point of memcached words can be used as a mutex to play.

Here are some summaries of the instructions:

1. Gets &cas should appear in pairs. The version number of a numeric type is obtained in the Get, which is set when CAS operates. But! If you change this number between get and CAS, CAS will fail.
2. The add operation cannot set duplicate key, otherwise it will fail.

Memcached (vii)--common instruction grasping packet analysis