CHEAT SHEET.pdf - DDBMS Extension of two-phase locking...

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• If coordinator fails, cohorts block until coordinator’s recovery to decide whether to commit or abort. | Independent recovery is not possible in two-phase commit . 2P 3P Schedule is serializable if it produces the same results as if the transactions were performed serially in some order. If Ti writes x, and then Tj reads x, draw edge from Ti to Tj If Ti reads x, and then Tj writes x, draw edge from Ti to Tj If Ti writes x, and then Tj writes x, draw edge from Ti to Tj Deadlock- two or more transactions wait for locks being held by each another cycle RSA Algorithm Choose p=3 and q=11 Compute n=p*q => 3*11 = 33 Compute φ(n)=(p -1)*(q- 1)=2*10=20 Choose e such that 1<e<φ(n) and e and φ(n) are coprime. Let e=7 Compute a value for d such that (d*e)% φ(n) =1. One solution is d=3 [(3*7)%20=1] Public key is (e, n) => (7,33) Private key is (d, n) => (3, 33) The encryption of M M = 2 C=2^7 % 33 = 29 The decryption of C C = 29 M = 29^3 %33 = 2 ----------------------------------------- Diffie-Hellman Example 1. Alice and Bob agree on p = 23 and g = 5. 2. Alice chooses a = 6 and sends 5^6 mod 23 = 8. 3. Bob chooses b = 15 and sends 5^15 mod 23 = 19. 4. Alice computes 19^6 mod 23 = 2. 5. Bob computes 8^15 mod 23 = 2. Then 2 is the shared secret. Transaction Management for DDBMS • Each site that initiates transactions has a transaction coordinator to manage transactions that originate there • Additional concurrency control problem Multiple-copy inconsistency problem • Solutions use locking and timestamping ----------------------------------------- Centralized All data at one site only • Replicated All data duplicated at all sites • Partitioned Data divided among sites Fragmentation scheme: horizontal, vertical, mixed fragments Each item appears only once • Hybrid Combination of the others Locking Protocols
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