What happens in the growing stage of two-phase locking?

• It collects every lock it needs and releases none
• The transaction releases locks and takes no new ones
• The transaction runs with no locks at all

What does isolation promise?

• Every transaction runs truly alone on its own machine
• Each behaves as if it has the database to itself
• Transactions may freely mix their changes together

Under snapshot isolation, a transaction reads from the picture taken when it started, no matter what others commit meanwhile.

Two transactions each hold a lock the other wants. What happens next?

• Both finish at double speed
• Neither moves, and the system cancels one side
• Both wait politely, then take turns without any help

Why must a transaction not release a lock early and take another one later?

• Another transaction could slip a change in between
• The later lock would be refused until the first commits
• Early release always crashes the database

What price does the database pay for offering snapshots?

• Keeping old row versions around for open pictures
• Blocking every writer until each long report finishes
• Deleting all pictures once a day

A friend says snapshots make all conflicts impossible. What is the best reply?

• Correct, pictures remove every clash
• Wrong for locks, but locks never wait either
• Wrong, same-row writes from one picture still clash at commit

Two transactions change the same row starting from the same picture. What must the system do at commit?

• Accept both writes quietly
• Delete the row entirely
• Catch the clash and let only one win