# DB2 - exercize session 01
##### 27 October 2015
## Concurrency Control

### View-Serializability VSR

Material on cs.unibg.it/mutti/

If we have the same __final writes__ and __read from__ of a serial schedule

- A __read-from__ means that the same object x was already written by another transaction,
different from the one whic is now reading x.
- A __final-write__ means that the object x is written and there are no others transaction

#### Exercize:
Classify the following schedules as non-vsr, vsr or csr.
```
r1(x) r2(y) w3(y) r5(x) w5(u) w3(s) w2(u) w3(x) w1(u) r4(y) w5(z) r5(z)
```
x|r1|r5
---|---|---
y|r2|w3
u|w5|w2
s|w3|
z||

### Blind writes

A write is said to be __blind__ if it is not the last action of resource X and the following action on X is a write wj(x)