Changes between Version 33 and Version 34 of VDEchp

Timestamp:

10/10/11 01:14:57 (13 years ago)

Author:

lvpeng

Comment:

--

VDEchp

@@ -28 +28 @@
 To compose a globally consistent state of all the VMs, the checkpoint of each VM must be coordinated. Besides checkpointing each VM’s correct state, it’s also essential to guarantee the consistency of all communication states within the virtual network. In Figure 2, the messages exchanged among the VMs are marked by arrows going from the sender to the receiver. The execution line of the VMs is separated by their corresponding checkpoints. The upper part of each checkpoint corresponds to the state before the checkpoint and the lower part of each checkpoint corresponds to the state after the checkpoint. A global checkpoint (consistent or not) is marked as the “cut” line, which separates each VM’s timeline into two parts. We label the messages exchanged in the virtual network into three categories:
 
- * (1) The state of the message’s source and the destination are on the same side of the cut line. For example, in Figure 2, both the source state and the destination state of message m,,1,, are above the cut line. Similarly, both the source state and the destination state of message m,,2,, are under the cut line.
+ * Type (1) message: The state of the message’s source and the destination are on the same side of the cut line. For example, in Figure 2, both the source state and the destination state of message m,,1,, are above the cut line. Similarly, both the source state and the destination state of message m,,2,, are under the cut line.
 
-(2) The message’s source state is above the cut line while the destination state is under the cut line, like message m,,3,,.
+ * Type (2) message: The message’s source state is above the cut line while the destination state is under the cut line, like message m,,3,,.
 
-(3) The message’s source state is under the cut line while the destination state is above the cut line, like message m,,4,,.
+ * Type (3) message: The message’s source state is under the cut line while the destination state is above the cut line, like message m,,4,,.
 
 For these three types of messages, we can see that a globally consistent cut must ensure the delivery of type (1) and type (2) messages, but avoid type (3) messages. For example, consider the message m,,4,,. In VM3’s checkpoint saved on the cut line, m,,4,, is already recorded as being received. However, in VM,,4,,’s checkpoint saved on the same cut line, it has no record that m4 has been sent out. Therefore, the state saved on VM,,4,,’s global cut is inconsistent, because in VM,,4,,’s view, VM,,3,, receives a message m,,4,,, which is sent by no one.