Deadlock

all_steps.md

1. Открываем два окна psql: session_1 и session_2;
2. В session_1:

BEGIN;
UPDATE bank_accounts SET amount = amount - 100 WHERE id = 1;

3. В session_2:

BEGIN;
UPDATE bank_accounts SET amount = amount + 100 WHERE id = 2;

4. В session_1:

UPDATE bank_accounts SET amount = amount + 50 WHERE id = 2;
COMMIT;

5. В session_2:

UPDATE bank_accounts SET amount = amount + 50 WHERE id = 1;
COMERROR:  deadlock detected
DETAIL:  Process 3225 waits for ShareLock on transaction 785; blocked by process 3002.
Process 3002 waits for ShareLock on transaction 786; blocked by process 3225.
HINT:  See server log for query details.
CONTEXT:  while updating tuple (0,5) in relation "bank_accounts"
ruslan=!# COMMIT;
ROLLBACK