Basic rules for locking
1.Agar data item main read lock hai to, transaction bas use read kar sakta hai .par update nahi kar sakta.
2.Agar ek transcation main kisi data item main read lock hain ,to other transaction same data item main read loack laga sakta hai par write lock nahi laga sakta.
3.Agar data item main write lock hain to transcation usme read aur update dono operation kar sakta hain.
4.Agar ek transaction ke kisi data item main write lock hain ,to koi aur transcation same data item main read aur write lock nahi laga sakte.
Modes of locking
1.SHARED LOCK:-
Agar transaction t1 ne item Q main shared mode lock laga hain to t1 bas read kar sakta hai par Q main write nai kar sakta.
Isko (S) se denote karte hain.
2.EXCLUSIVE LOCK:-
Agar transaction t1 main data item Q main exclusive mode lock laga hain to ,t1 Q ko read aur write dono kar sakta hain. isko (X) se denote karte hain.
Two Phase locking protocol
Two phase locking protocol serializability ensure karne ke liye use hoti .Is protocol main transaction lock and unlock request ko do phase main apply karta hai
1.Growing Phase:-
Is phase main transaction bas lock laga sakta hai par kisi lock ko release nahi kar sakta.
2.Shrinking phase:-
Is phase main transaction locks ko release karta hai par koi lock laga nai sakta.
Two phase locking protocol teen type ke hote hain
1.Conservative Two phase locking:
Is protocol main transaction sabhi data item ko uske use hone se pahle lock laga deta hain.Agar koi data item lock nai hota to transaction use lock hone tak waiting state main chala jata hain.
2.Strict Two phase locking :
Is protocol main transaction koi bhi write lock release nahi karta jab tak ki transaction commit ya abort na ho jaye.
3.Rigorous Two phase Locking
Is protocol main transaction koi bhi write lock aur read lock release nahi karta jab tak ki transaction commit ya abort na ho jaye.
1.Agar data item main read lock hai to, transaction bas use read kar sakta hai .par update nahi kar sakta.
2.Agar ek transcation main kisi data item main read lock hain ,to other transaction same data item main read loack laga sakta hai par write lock nahi laga sakta.
3.Agar data item main write lock hain to transcation usme read aur update dono operation kar sakta hain.
4.Agar ek transaction ke kisi data item main write lock hain ,to koi aur transcation same data item main read aur write lock nahi laga sakte.
Modes of locking
1.SHARED LOCK:-
Agar transaction t1 ne item Q main shared mode lock laga hain to t1 bas read kar sakta hai par Q main write nai kar sakta.
Isko (S) se denote karte hain.
2.EXCLUSIVE LOCK:-
Agar transaction t1 main data item Q main exclusive mode lock laga hain to ,t1 Q ko read aur write dono kar sakta hain. isko (X) se denote karte hain.
Two Phase locking protocol
Two phase locking protocol serializability ensure karne ke liye use hoti .Is protocol main transaction lock and unlock request ko do phase main apply karta hai
1.Growing Phase:-
Is phase main transaction bas lock laga sakta hai par kisi lock ko release nahi kar sakta.
2.Shrinking phase:-
Is phase main transaction locks ko release karta hai par koi lock laga nai sakta.
Two phase locking protocol teen type ke hote hain
1.Conservative Two phase locking:
Is protocol main transaction sabhi data item ko uske use hone se pahle lock laga deta hain.Agar koi data item lock nai hota to transaction use lock hone tak waiting state main chala jata hain.
2.Strict Two phase locking :
Is protocol main transaction koi bhi write lock release nahi karta jab tak ki transaction commit ya abort na ho jaye.
3.Rigorous Two phase Locking
Is protocol main transaction koi bhi write lock aur read lock release nahi karta jab tak ki transaction commit ya abort na ho jaye.
