2 distributed

7

.

2.1 (distributed database)

. (distributed DBMS) [OV91].

. " " " ". . / .

.

, , , : , ,

,

8

, ,

, , ,

, , ,

. , ,

.

. : .

(administrators) , . .

.

. , ( - ) -, , .

, , .

, , , , .

, ( - - ) , , . .

2.2

, . , , : . , . , [CP84].

9

2.2.1 2.1

. .

1

2

1 2

1

2 ...

2.1

(global schema).

, . , . ( ) (global relations).

, , (fragments). , (fragmentation schema). , [CP84] , . , , Ri i R.

. , , . , . (allocation schema).

10

, - . R j (physical image) R j, Rj. (copy of a fragment) Ri j Rij.

, , (local mapping schema) .

. : .

: (fragmetnation transparency) (location transparency). , . " " .

. , . (local mapping transparency) .

. , . , . , , (replication transparency).

.

2.2.2

: (horizontal fragmentation) (vertical fragmentation). , , , . , :

1. (completeness). ( ).

2. (reconstruction). . , ,

11

.

3. (disjointness). , ( , , ). .

2.2.3 (horizontal fragmentation)

(tuples) ( , , ). (selection) .

PROJECT (PNUM, NAME, BUDGET, CITY)

PROJECT1 = CITY='ATH' PROJECT PROJECT2 = CITY='SAL' PROJECT , :

CITY PROJECT, ,

PROJECT = PROJECT1 PROJECT2 ,

. , (XOR) .

, , . , ,

DEPT_TASK (EMPNUM, PNUM, ROLE) EMPNUM PROJECT PNUM. DEPT_TASK . , CITY DEPT_TASK. :

DEPT_TASK1 = DEPT_TASK >< PNUM = PNUM PROJECT1 DEPT_TASK2 = DEPT_TASK >< PNUM = PNUM PROJECT2 semi-join1 DEPT_TASK1

DEPT_TASK . (derived fragmentation). :

1 semi-join >< : R >< A = B S = (R >< A = B S)

12

DEPT_TASK PROJECT ( ).

. DEPT_TASK

PROJECT . , - .

2.2.4 (vertical fragmentation)

. ( join) . , :

EMP (EMPNUM, NAME, SALARY, TAX, MGRNUM, DEPTNUM)

EMP1 = EMPNUM, NAME, MGRNUM, DEPTNUM EMP EMP2 = EMPNUM, SAL, TAX EMP

EMP = EMP1 >< EMPNUM = EMPNUM EMP2

EMPNUM EMP. . , , , .

, , EMPNUM, .

, , . , , . ( ) - - , .

2.2.5 (mixed fragmentation)

. .

EMP (EMPNUM, NAME, SALARY, TAX, MGRNUM, DEPTNUM) :

EMP1 = DEPTNUM 10 EMPNUM, NAME, MGRNUM, DEPTNUM EMP EMP2 = 10 < DEPTNUM 20 EMPNUM, NAME, MGRNUM, DEPTNUM EMP EMP3 = DEPTNUM > 20 EMPNUM, NAME, MGRNUM, DEPTNUM EMP

13

EMP4 = EMPNUM, NAME, SAL, TAX EMP :

EMP = (EMP1,EMP2, EMP3) >< EMPNUM = EMPNUM (EMPNUM, SAL, TAX EMP4)

2.2. , (fragmetation tree), , .

EMP

EMP4

EMP1 EMP2 EMP3

2.2

2.3

: top-down bottom-up2. , - , , ( ) .

top-down , . 2.3 [OV91] top-down .

2 bottom-up . [CP84], [OV91] .

14

Interface

Feedback Feedback

2.3 Top-down

' ,

. : interface (conceptual design). , . , : , , , ,

15

. interface .

(global conceptual schema) , . .

(local conceptual schemata). , .

, , . .

, : .

2.3.1

. , "" . . , ( ), . . , ( ) . .

, - - , ( ). , (primary), (derived), .

' , . , [CP84].

R . (simple predicate) :

= (minterm predicate) y P, P , , . :

16

y = AND (pi*), pi P, pi* = pi pi* = pi, y false (fragment) . , pi P P, pi . , pi - , .

P = {p1, p2, ..., pn} . , P , P (complete) (minimal). P P, . P , , , .

. : R: , P: : P': : F: (f: P'). begin

pi P, .. pi R ; P' := {pi}; P := P - {pi}; F := {fi}; { pi} do

begin pj .. pj fj P' ; P' := P' {pj}; P := P - {pj}; F := F {fj}; if pk P' then begin

P' := P' - {pk}; F := F - {fk};

end-if until P'

end. P',

P. ,

17

(.. , .)

, , [CP84].

. .., 2

4004 . . , - ;- . : . , . , , . , . , , . :

EMP (EMPNUM, NAME, SALARY, TAX, MGRNUM, DEPTNUM) DEPT (DEPTNUM, NAME, AREA, MGRNUM) DEPT_TASK(DEPTNUM, TNUM, ROLE, BUDGET) TASK (TNUM, NAME, PROGRESS, CITY)

' , TASK. , ,

'KAST', 'RHO', 'ATH' . . :

SELECT NAME, PROGRESS FROM TASK WHERE TNUM = $1;

. , 80%. . . :

p1: CITY = 'KAST' p2: CITY = 'RHO'

{p1, p2} . :

q1: CITY = 'KAST' AND CITY = 'RHO' q2: CITY = 'KAST' AND NOT (CITY = 'RHO') q3: NOT (CITY = 'KAST') AND CITY = 'RHO' q4: NOT(CITY = 'KAST') AND NOT (CITY = 'RHO')

q1 q4 . ,

CITY = 'KAST' => (CITY = 'RHO') CITY = 'RHO' => (CITY = 'CAST')

18

q2, q3 p1, p2 {p1, p2} .

query CITY, , TNUM CITY.

TASK : TASK1 = CITY='KAST' TASK TASK2 = CITY='RHO' TASK

DEPT : .

( ).

. , .

: p1: CITY = 'KAST' p2: CITY = 'RHO' p3: CITY = 'ATH' p4: AREA = 'NORTH' p5: AREA = 'SOUTH'

DEPTNUM 1 10, 11 20 21 30. :

p1: DEPTNUM < 10 p2: 10 < DEPTNUM < 20 p3: DEPTNUM > 20 p4: AREA = 'NORTH' p5: AREA = 'SOUTH'

( ) :

q1: DEPTNUM < 10 q2: 10 < DEPTNUM < 20 AND AREA = 'NORTH' q3: 10 < DEPTNUM < 20 AND AREA = 'SOUTH' q4: DEPTNUM > 20

, DEPT : DEPT1 = DEPTNUM 10 DEPT DEPT2 = 10 < DEPTNUM 20 AND AREA = 'NORTH' DEPT DEPT3 = 10 < DEPTNUM 20 AND AREA = 'SOUTH' DEPT DEPT4 = DEPTNUM > 20 DEPT

, . (distributed join) . , R S, R S. , Ri Sj.

19

(join graph). G (, ) R S , . 2.4 .

(total) (reduced) . : (partitioned)

. (simple)

. 2.4 .

R1

R2

R3

S1

S2

()

R1

R2

R3

S1

S2

()

R1 S1

R2 S2

R3 S3

()

2.4

, joins ( ).

, semi-join , . , :

. DEPT_TASK.

DEPT_TASK: (

DEPT_TASK >

20

( DEPT_TASK >< TNUM = TNUM TASK1 DEPT_TASK2 = DEPT_TASK >< TNUM = TNUM TASK2

DEPT_TASK1 = DEPT_TASK >< DEPTNUM = DEPTNUM DEPT1 DEPT_TASK2 = DEPT_TASK >< DEPTNUM = DEPTNUM DEPT2 DEPT_TASK3 = DEPT_TASK >< DEPTNUM = DEPTNUM DEPT3 DEPT_TASK4 = DEPT_TASK >< DEPTNUM = DEPTNUM DEPT4 semi-join

. . , , , semi-joins - .

. , , . . , .

, (greedy) . , (split approach) , (grouping approach) , .

( ) (replication). . , , .

, , , . , , .

. EMP.

EMP:

/ ( NAME, SAL, TAX)

21

( NAME, MGRNUM DEPTNUM)

EMP : EMP1 (EMPNUM, NAME, SALARY, TAX) EMP2 (EMPNUM, NAME, MGRNUM, DEPTNUM)

(EMPNUM) . , NAME. , , . , , , , .

, , EMP2 DEPT. , EMP:

EMP1 (EMPNUM, NAME, SALARY, TAX) EMP2 (EMPNUM, NAME, MGRNUM, DEPTNUM)- EMP3 = EMP2 >< DEPTNUM = DEPTNUM DEPT1 EMP4 = EMP2 >< DEPTNUM = DEPTNUM DEPT2 EMP5 = EMP2 >< DEPTNUM = DEPTNUM DEPT3 EMP6 = EMP2 >< DEPTNUM = DEPTNUM DEPT4

semi-join .

2.3.2

(fragment allocation) , . : , , .

, (best fit): . , .

, , , : "" (all benefitial sites)

. .

(additional replication) ( ) .

, , [CP84]. . :

22

i j k fkj k j rki k i uki k i nki k i (nki = rki +

uki)

(

). Ri . j :

Bij = k fkj nki Ri j Bij .

"" Ri . i j :

Bij = k fkj rki - C k j' j fkj' uki To C ( - ). Ri Bij . Bij , .

, . ' , , , . di Ri Fi Ri , :

(di) = (1 - 21 - di) Fi ,

Ri. i j:

Bij = k fkj rki - C k j' j fkj' uki - (di)

, . Ri r, Rs Rt s t . :

23

As At s t Rs Rt . .

1 r Rs Rt. , , r.

2 r Rs Rt. ( ) s t.

3 r, s, t Rs Rt. ( r, s t).

:

Bist = kAs fks nki + kAt fkt nki - kA1 fkr nki - kA2 2 fkr nki - kA3 j r, s, t fkj nki

(nki). nki rki + C uki.

, Ri r, Rs Rt s t . , : As s

Rs Rs . At.

2 r ( Rs Rt).

3 r, s, t Rs Rt.

.

2.4

,

. , , . , . , (global queries) (fragment queries)

24

. (, ). , [CP84].

2.4.1

. . , . , , . , :

NAME, DEPTNUM DEPTNUM = 15 EMP DEPTNUM = 15 NAME, DEPTNUM EMP

(operator tree). .

TNUM, ROLE CITY = 'RHO' (TASK >< DEPT_TASK) 2.5:

EMPNUM, ROLE

CITY='RHO'

>

25

, . , , , . U , R.

U1 U2 R U2 U1 R

R1 B R2 R2 R1

R1 B (R2 B R3) (R1 R2) B R3

U R U1 U2 R

U(R1) B U(R2) U(R1 R2) . ,

. , , . [OV91], [CP84] . , :

1. .

. :

A1 F2 R = F2 A1 R, Attr(F2) A1 2. .

.

R1 >

26

(R1 R2) >< (S1 S2) = (R1 >< S1) (R1 >< S2) (R2 >< S1) (R2 >< S2)

,

( R1, R2, S1, S2 R, S R >< S).

2.4.2

. (canonical expression), , . : . ( , , ).

. , , . , , . , , . , 2.6 2.7, . 2.5

TNUM, ROLE

>

27

TNUM, ROLE

CITY='RHO'

>< DEPT_TASK), TASK1 TASK2, .

2. , . , TASK1, TNUM CITY='RHO'(TASK1), .

3. ( ), . , CITY='RHO' (TASK2) CITY='RHO'CITY='KAST' (TASK), . (, , ).

28

4. , , ( ). , , .

5. -, . , DEPTNUM < 10 AREA = NORTH, , AREA = SOUTH DEPT_TASK DEPTNUM < 10.

6. semi-joins joins, .

semi-joins

(join) ,

. , , , . semi-join , .

, , , semi-join. , . R S [OV91]:

R >

29

>

30

, :

(bytes) S# 4 P# 4 QTY 10

SNAME 96 PNAME 196

, , 4

S >< SP >< P (

) (). .

semi-join. ' semi-join,

. , S, SP P. , : S (S#, SNAME) 6

4+96=100 bytes. , S 6x100 bytes=600 bytes. SP (S#, P#, QTY) 8

4+4+10=18 bytes. , SP 8x18 bytes=144 bytes. P (P#, PNAME) 6

4+196=200 bytes. , P 6x200 bytes=1200 bytes. S JOIN SP JOIN P, R,

8 : R(S#, SNAME, P#, PNAME, QTY)3. 4+96+4+196+10=310 bytes. , R 8310 bytes=2480 bytes.

, S >< SP >< P 4, , ( R) 4 . R, , . CR= 2480 bytes.

, 1 2 3, , 2480 bytes, .

, , S, SP P 4 , .

3 R(S#, SNAME, P#, PNAME, S#, P#, QTY). , .

31

S, SP P 4, 600+144+1200=1944 bytes.

S >< SP

S >< SP. : ' S# SP 2 1. semi-join S'. , 4, S', SP, P . SP 4, semi-join 1. , :

2, S# SP. : F = S#(SP). F 3 : s1, s2, s3. 1, S. , 34=12 bytes.

1, join S S# 2, : S'= F >< S. S' 3(4+96)=300 bytes.

, S 1 4, 300 bytes. S >< SP, 1 4 S, .

, , SP 2 4 (144 bytes) P 3 4 (1200 bytes).

, 4, R = S' >< SP >< P. , S >< SP, : 12+300+144+1200=1656 bytes.

, semi-joins S# P# SP 3

S#, P#. , S# S P# P 6 . S# P# S, SP P, , S# P#, SP.

, : i) S# SP 2

F=S#(SP), C1=12 bytes, 1. ii) , P# SP 2

G=P#(SP), C1=12 bytes, 3. iii) F=S >

32

vii), G, C3=600 bytes, 3 F" >

33

2.5.1

. 2.9 [OV91]

. monitor . monitor : (transaction manager) (scheduler). . . - - (recovery managers). , .

. monitor , monitor , , .

Begin_transaction,

Read, Write,Commit, Abort

monitor

2.9 monitor

2.5.2

(serializability), , - -, , . , .

34

(schedule) ( -local schedule) (global schedule). , . , . . , [OV91],

, x :

1: Read(x)

x := x + 5 Write(x) Commit

2: Read(x) x := 10 * x Write(x) Commit

.

: S1 = {R1(x), W1(x), C1, R2(x), W2(x), C2} S2 = {R2(x), W2(x), C2, R1(x), W1(x), C1}

( ), , . x 1. , 60, 15, .

, . (one-copy serializable).

x x1, x2, ..., xn. x (logical data) (physical data). , . , , , read once/write all (ROWA).

2.5.3

. . - - , :

35

(optimistic) , . (pessimistic) . , .

, : (lockings), (timestamps). , . , .

, , , . , (lock manager). : (centralized locking),

.

(primary copy locking) , . .

(decentralized locking), . . , , .

2.5.4

(2 Phase Locking - 2PL). O : read-lock (Shared - S) write-lock (eXclusive -X). , read-lock . , , write-lock . (lock) . O 2 Phase Locking, : , , . .

1 2 . 2 , ( 1, 2, 2 ):

36

S X S X

,

(physical locking) (logical locking). , . , . , , , , : , . , ' . .

, , . 2PL . .

2.10 . (. [OV91]).

Monitor

1.

2.

3.

4.

5.

2.10

bottleneck ,

37

. , , .

, . . "" (, ) . . , , .

- . ' , ' .

, 2PL , . . , , . . , bottleneck , , . 2.11 2PL .

Monitor

1.

3.

2.

4.

2.11 2PL

2.6

(COMMIT & RECOVERY OF DISTRIBUTED TRANSACTIONS)

.

38

, .

2.6.1

:

1. . , , (abort) (divide by zero, ). , (rollback) .

2. . , - (.. ) . . , .

3. . , . (media failures). . ' , .

2.6.2 -

(log). : ( undo)

, (commit) ,

( redo) , (.. buffers ).

: . , : (tupleID) record record .

,

39

. . write-ahead log, . write-ahead log : ,

. ,

. ,

(checkpoints) . (.. ) , , . : records

buffers

. ,

, .

, log . backup . , .

2.6.3

. , monitors : begin_transaction, read, write, abort, commit, recover. begin_transaction, read write (.. ROWA). , , . , ( monitor, ) (coodinator) . monitors , .

: (termination) . , , , . , , , .

40

- 2 Phase Commit (2PC)

, : .

, , , .

, .

, (2 Phase Commit - 2PC) . To 2PC (commit) . ( , ). 2PC , :

' , record "begin_transaction" ( ). , "prepare" "WAIT". "prepare" . , record "ready", "vote-commit" "READY". , , record "ABORT" "vote-abort" . , , . . , "" . , . , "commit" record , "global-commit" record "COMMIT". , "abort" record , "global-abort" "ABORT". . "end-of-transaction" record . 2.12.

41

preparevote-abort/

vote-commitglobal-abort/

global-commitaborted/

commited

2.12 2 Phase Commit - 2PC

2PC (centralized 2PC)

. (. [OV91]) 2PC (distributed 2PC). , , "prepare" . , (, ).

preparevote-abort/

vote-commitglobal-abort/

global-commit

2.13 2PC ,

. , , , "" . 2PC , ( veto)

42

. (. [OV91]), timeouts. , :

1. . , timeout, . , , timeout, - , .

2. "ready" record . timeout , . , .

3. "ready" record "READY" . , . , .

4. "prepare" record "global_commit" record . . , "prepare" ( ) . "prepare", .

5. "global_commit" record , "end-of-transaction" record. .

6. . , , 2 3, , 4 5.

, , , . , 2PC. :

( , , )

. : 2PC

. , , ( ). ( ) . [OV91].

43

, .

2.7

[OV91] M.T. Ozsu, P. Valduriez. Principles of Distributed Database Systems. Prentice-

Hall, 1991 [CP84] S. Ceri, G. Pelagatti. Distributed Databases -Principles and Systems. McGraw-

Hill, 1984 [Oz93] T. Ozsu, "Transaction models and transaction management in object-oriented

database systems", NATO Advanced Study Institute, Object-Oriented Database System, Kusadasi Turkiye, August 1993

44