ACID. , . (integrity). , , : (domain integrity), (referential integrity), (entity integrity), .
. , , , , . - , . - , , .
, , . , , , . , , . , , . .
Isolation
. Repeatable Read .
Durability
( , ) , , . , , , , - - .
.
́ , , , , . , . , , , .
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, , . , , .[1]
, , .
, , ( (. ). ^ . .), . . , , , - , , . , , , , . , , , .
:
1. .
2. .
3. .
.
, . 11.1. , : R t1.
FETCH R | t1 | |||
t2 | FETCH R | |||
UPDATE R | t3 | |||
t4 | UPDATE R | |||
. 11.1. t4
R t2. t3 , t1, t4, , t2, , , t1. , , t4, , .
^
, , , , , . , , , . , , . . 11.2 11.3.
t1 | UPDATE R | |||
FETCH R | t2 | |||
t3 | ROLLBACK | |||
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|
. 11.2. t2
t1 | UPDATE R | |||
UPDATE R | t2 | |||
t3 | ROLLBACK | |||
. 11.3. t2 t3
(. 11.2) ( ) t2. t3 . , , , R , t2, , t1. , . , , ( ROLLBACK) - . , , . ( . ROLLBACK .)
(. 11.3) . t2, t3, ROLLBACK t3 R , t1. .
^
. 11.4, , . , 10 3 1. 110, , , , . , . . , , 3.
1 | 2 | 3 | ||||
40 | 50 | 30 | ||||
^ FETCH 1 (40): == 40 | t1 | |||||
^ FETCH 2 (50): = 90 | t2 | |||||
t3 | ^ FETCH 3 (30) | |||||
t4 | ^ UPDATE 3: 3020 | |||||
t5 | ^ FETCH 1 (40) | |||||
t6 | ^ UPDATE 1: 4050 | |||||
t7 | COMMIT | |||||
FETCH 3 (20): =110, 120 | t8 | |||||
. 11.4.