Add the operation commit at the end of each of the transactions T 1 and T 2 from Figure 21.2; then list all possible schedules for the modified transactions. Determine which of the schedules are recoverable, which are cascadeless, and which are strict.
What will be an ideal response?
T 1 T 2
read_item(X); read_item(X);
X := X - N X := X + M;
write_item(X); write_item(X);
read_item(Y); commit T 2
Y := Y + N;
write_item(Y);
commit T 1
The transactions can be written as follows using the shorthand notation:
T 1 : r 1 (X); w 1 (X); r 1 (Y); w 1 (Y); C 1 ;
T 2 : r 2 (X); w 2 (X); C 2 ;
In general, given m transactions with number of operations n1, n2, ..., nm, the number of possible schedules is: (n1 + n2 + ... + nm)! / (n1! * n2! * ... * nm!), where ! is the factorial function. In our case, m =2 and n1 = 5 and n2 = 3, so the number of possible schedules is:
(5+3)! / (5! * 3!) = 8*7*6*5*4*3*2*1/ 5*4*3*2*1*3*2*1 = 56.
Below are the 56 possible schedules, and the type of each schedule:
S 1 : r 1 (X); w 1 (X); r 1 (Y); w 1 (Y); C 1 ; r 2 (X); w 2 (X); C 2 ; strict (and hence
cascadeless)
S 2 : r 1 (X); w 1 (X); r 1 (Y); w 1 (Y); r 2 (X); C 1 ; w 2 (X); C 2 ; recoverable
S 3 : r 1 (X); w 1 (X); r 1 (Y); w 1 (Y); r 2 (X); w 2 (X); C 1 ; C 2 ; recoverable
S 4 : r 1 (X); w 1 (X); r 1 (Y); w 1 (Y); r 2 (X); w 2 (X); C 2 ; C 1 ; non-recoverable
S 5 : r 1 (X); w 1 (X); r 1 (Y); r 2 (X); w 1 (Y); C 1 ; w 2 (X); C 2 ; recoverable
S 6 : r 1 (X); w 1 (X); r 1 (Y); r 2 (X); w 1 (Y); w 2 (X); C 1 ; C 2 ; recoverable
S 7 : r 1 (X); w 1 (X); r 1 (Y); r 2 (X); w 1 (Y); w 2 (X); C 2 ; C 1 ; non-recoverable
S 8 : r 1 (X); w 1 (X); r 1 (Y); r 2 (X); w 2 (X); w 1 (Y); C 1 ; C 2 ; recoverable
S 9 : r 1 (X); w 1 (X); r 1 (Y); r 2 (X); w 2 (X); w 1 (Y); C 2 ; C 1 ; non-recoverable
S 10 : r 1 (X); w 1 (X); r 1 (Y); r 2 (X); w 2 (X); C 2 ; w 1 (Y); C 1 ; non-recoverable
S 11 : r 1 (X); w 1 (X); r 2 (X); r 1 (Y); w 1 (Y); C 1 ; w 2 (X); C 2 ; recoverable
S 12 : r 1 (X); w 1 (X); r 2 (X); r 1 (Y); w 1 (Y); w 2 (X); C 1 ; C 2 ; recoverable
S 13 : r 1 (X); w 1 (X); r 2 (X); r 1 (Y); w 1 (Y); w 2 (X); C 2 ; C 1 ; non-recoverable
S 14 : r 1 (X); w 1 (X); r 2 (X); r 1 (Y); w 2 (X); w 1 (Y); C 1 ; C 2 ; recoverable
S 15 : r 1 (X); w 1 (X); r 2 (X); r 1 (Y); w 2 (X); w 1 (Y); C 2 ; C 1 ; non-recoverable
S 16 : r 1 (X); w 1 (X); r 2 (X); r 1 (Y); w 2 (X); C 2 ; w 1 (Y); C 1 ; non-recoverable
S 17 : r 1 (X); w 1 (X); r 2 (X); w 2 (X); r 1 (Y); w 1 (Y); C 1 ; C 2 ; recoverable
S 18 : r 1 (X); w 1 (X); r 2 (X); w 2 (X); r 1 (Y); w 1 (Y); C 2 ; C 1 ; non-recoverable
S 19 : r 1 (X); w 1 (X); r 2 (X); w 2 (X); r 1 (Y); C 2 ; w 1 (Y); C 1 ; non-recoverable
S 20 : r 1 (X); w 1 (X); r 2 (X); w 2 (X); C 2 ; r 1 (Y); w 1 (Y); C 1 ; non-recoverable
S 21 : r 1 (X); r 2 (X); w 1 (X); r 1 (Y); w 1 (Y); C 1 ; w 2 (X); C 2 ; strict (and hence
cascadeless)
S 22 : r 1 (X); r 2 (X); w 1 (X); r 1 (Y); w 1 (Y); w 2 (X); C 1 ; C 2 ; cascadeless
S 23 : r 1 (X); r 2 (X); w 1 (X); r 1 (Y); w 1 (Y); w 2 (X); C 2 ; C 1 ; cascadeless
S 24 : r 1 (X); r 2 (X); w 1 (X); r 1 (Y); w 2 (X); w 1 (Y); C 1 ; C 2 ; cascadeless
S 25 : r 1 (X); r 2 (X); w 1 (X); r 1 (Y); w 2 (X); w 1 (Y); C 2 ; C 1 ; cascadeless
S 26 : r 1 (X); r 2 (X); w 1 (X); r 1 (Y); w 2 (X); C 2 ; w 1 (Y); C 1 ; cascadeless
S 27 : r 1 (X); r 2 (X); w 1 (X); w 2 (X); r 1 (Y); w 1 (Y); C 1 ; C 2 ; cascadeless
S 28 : r 1 (X); r 2 (X); w 1 (X); w 2 (X); r 1 (Y); w 1 (Y); C 2 ; C 1 ; cascadeless
S 29 : r 1 (X); r 2 (X); w 1 (X); w 2 (X); r 1 (Y); C 2 ; w 1 (Y); C 1 ; cascadeless
S 30 : r 1 (X); r 2 (X); w 1 (X); w 2 (X); C 2 ; r 1 (Y); w 1 (Y); C 1 ; cascadeless
S 31 : r 1 (X); r 2 (X); w 2 (X); w 1 (X); r 1 (Y); w 1 (Y); C 1 ; C 2 ; cascadeless
S 32 : r 1 (X); r 2 (X); w 2 (X); w 1 (X); r 1 (Y); w 1 (Y); C 2 ; C 1 ; cascadeless
S 33 : r 1 (X); r 2 (X); w 2 (X); w 1 (X); r 1 (Y); C 2 ; w 1 (Y); C 1 ; cascadeless
S 34 : r 1 (X); r 2 (X); w 2 (X); w 1 (X); C 2 ; r 1 (Y); w 1 (Y); C 1 ; cascadeless
S 35 : r 1 (X); r 2 (X); w 2 (X); C 2 ; w 1 (X); r 1 (Y); w 1 (Y); C 1 ; strict (and hence
cascadeless)
S 36 : r 2 (X); r 1 (X); w 1 (X); r 1 (Y); w 1 (Y); C 1 ; w 2 (X); C 2 ; strict (and hence
cascadeless)
S 37 : r 2 (X); r 1 (X); w 1 (X); r 1 (Y); w 1 (Y); w 2 (X); C 1 ; C 2 ; cascadeless
S 38 : r 2 (X); r 1 (X); w 1 (X); r 1 (Y); w 1 (Y); w 2 (X); C 2 ; C 1 ; cascadeless
S 39 : r 2 (X); r 1 (X); w 1 (X); r 1 (Y); w 2 (X); w 1 (Y); C 1 ; C 2 ; cascadeless
S 40 : r 2 (X); r 1 (X); w 1 (X); r 1 (Y); w 2 (X); w 1 (Y); C 2 ; C 1 ; cascadeless
S 41 : r 2 (X); r 1 (X); w 1 (X); r 1 (Y); w 2 (X); C 2 ; w 1 (Y); C 1 ; cascadeless
S 42 : r 2 (X); r 1 (X); w 1 (X); w 2 (X); r 1 (Y); w 1 (Y); C 1 ; C 2 ; cascadeless
S 43 : r 2 (X); r 1 (X); w 1 (X); w 2 (X); r 1 (Y); w 1 (Y); C 2 ; C 1 ; cascadeless
S 44 : r 2 (X); r 1 (X); w 1 (X); w 2 (X); r 1 (Y); C 2 ; w 1 (Y); C 1 ; cascadeless
S 45 : r 2 (X); r 1 (X); w 1 (X); w 2 (X); C 2 ; r 1 (Y); w 1 (Y); C 1 ; cascadeless
S 46 : r 2 (X); r 1 (X); w 2 (X); w 1 (X); r 1 (Y); w 1 (Y); C 1 ; C 2 ; cascadeless
S 47 : r 2 (X); r 1 (X); w 2 (X); w 1 (X); r 1 (Y); w 1 (Y); C 2 ; C 1 ; cascadeless
S 48 : r 2 (X); r 1 (X); w 2 (X); w 1 (X); r 1 (Y); C 2 ; w 1 (Y); C 1 ; cascadeless
S 49 : r 2 (X); r 1 (X); w 2 (X); w 1 (X); C 2 ; r 1 (Y); w 1 (Y); C 1 ; cascadeless
S 50 : r 2 (X); r 1 (X); w 2 (X); C 2 ; w 1 (X); r 1 (Y); w 1 (Y); C 1 ; cascadeless
S 51 : r 2 (X); w 2 (X); r 1 (X); w 1 (X); r 1 (Y); w 1 (Y); C 1 ; C 2 ; non-recoverable
S 52 : r 2 (X); w 2 (X); r 1 (X); w 1 (X); r 1 (Y); w 1 (Y); C 2 ; C 1 ; recoverable
S 53 : r 2 (X); w 2 (X); r 1 (X); w 1 (X); r 1 (Y); C 2 ; w 1 (Y); C 1 ; recoverable
S 54 : r 2 (X); w 2 (X); r 1 (X); w 1 (X); C 2 ; r 1 (Y); w 1 (Y); C 1 ; recoverable
S 55 : r 2 (X); w 2 (X); r 1 (X); C 2 ; w 1 (X); r 1 (Y); w 1 (Y); C 1 ; recoverable
S 56 : r 2 (X); w 2 (X); C 2 ; r 1 (X); w 1 (X); r 1 (Y); w 1 (Y); C 1 ; strict (and hence
cascadeless)
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