Concurrency Control

Recoverability requires T1 must commit before T2 does.

T1: write(A)
T2: read(A)
T2: commit
T1: abort

here show a read-from dependency

Commit is related to abort. Not commit means maybe abort. So to reduce the cascade cost, we have the strict 2PL . strict 2PL : Lock-X release only after commit. rigorous 2PL : All lock release only after commit.