**5.5 Dynamic adjusting mechanism for cache node**

Because of the unstable of the cache node, the cache node can be joined or disjoined in dynamic. So the grid memory is changed in PCMGM. The dynamic adjusting mechanism for cache node must be discussed. We call the cache node which can't work for grid as the *failure cache node* and the new joined computer as the *new cache node*.

**Definition.8. Computing density vector** is defined as *CDV*= (*cd1*, *cd2*… *cdp*), where *cdi* is the value of density allocation strategy of *CNi*. If *cdi* <*d,* we call *CNi* as the *low-density cache node*; If *cdi* >*d,* we call *CNi* as the *high-density cache node*;

**Definition.9. Failure storage matrix** is defined as *FSM*= *(fqij)* (1≤*i*≤*m*, 1≤*j*≤*k*), where *fqij is DSEG* numbers of the *j* th segment of *CFi*, which *DSEG*s are stored in the *failure cache node*.

**Definition.10. effective storage matrix** is defined as *ESM*= *(eqij)* (1≤*i*≤*m*, 1≤*j*≤*k*), and *ESM*=*NCDM*-*FSM*.

**Definition.11. Migration storage matrix** is defined as *MSM*= *(mqij)* (1≤*i*≤*m*, 1≤*j*≤*k*), where *mqij* is *DSEG* numbers of the *j* th segment of *CFi*, which *DSEG*s are stored in the *failure (or overload ) cache node* , and the *DSEG*s of *MSM* will be migrated.
