??a?e???s? S??a??a???

1
15

• ??a?e???s? S??a??a???

• S??a??a???
• ??e???? ta?t??????sµ??
• ?pa???t?s? ded?µ????

2
?ef??a?? 15 ??a?e???s? S??a??a???
S??a??a???

• ??a s????? ?e?t??????? t? ?p??? ap?te?e? µ?a
  ?????? ?e?t??????? µ???da ?a?e?ta? s??a??a??
  (transaction).
• ??a s??a??a?? pe????e?
• e?t???? a?????s??,
• e?t???? e?sa?????,
• e?t???? d?a??af??, ?
• e?t???? e??µ???s??
• t?? ded?µ???? t?? ??.

3
?ef??a?? 15 ??a?e???s? S??a??a???
S??a??a???

• ? p???p????t?ta t?? s???????? ß?se?? ded?µ????
  ?d??e? st?? a??pt??? a???p?st?? µ??a??sµ??
  e?????? t?? a?e?a??t?ta? t?? ded?µ????
• p????? s??a??a??? µp??e? ?a ß??s???ta? se
  e??????, p??spe?a????ta? ????? ded?µ??a
• ? ??e???? ta?t??????sµ?? (concurrency control)
  d?a?e????eta? t?? s??a??a??? ?ts? ?ste ?a
  ap?fe????ta? ?? pa????????? ?atast?se??

4
?ef??a?? 15 ??a?e???s? S??a??a???
S??a??a???

• ??a ?? µp??e? ?a ß?e?e? se asta?? ?at?stas?
• ap? µ?a ß??ß? t?? s?st?µat?? (ß??ß? t?? f?s????
  µ?s?? ap????e?s??) ? (????? µ????? t??
  s?st?µat??),
• µet? t?? ap??at?stas? t?? ß??ß?? p?a?µat?p??e?ta?
  ??e???? t?? ded?µ????.
• ?p???e? a????? ?pa???? µ??a??sµ?? epa???t?s??
  (recovery) ded?µ????, ?ste ?a epa????e? ? ?? st??
  ?a?????? t?? ?at?stas? ?p?? p??????ta? ???? ??
  pe?????sµ?? a?e?a??t?ta?.

5
?ef??a?? 15 ??a?e???s? S??a??a???
S??a??a???

• ??a s??a??a?? e??a? s?????? t? ap?t??esµa t??
  e?t??es?? e??? p?????µµat?? p?? e??a? ??aµµ??? se
  µ?a ???ssa p????aµµat?sµ?? ?????? ep?p?d??.
• ?? e?t???? p?? p??sd???????? µ?a s??a??a??
  pe????e???ta? µeta?? t?? e?f??se??
• BEGIN TRANSACTION, ?a?
• END TRANSACTION.

6
?ef??a?? 15 ??a?e???s? S??a??a???
?atast?se?? S??a??a???

• ??a s??a??a?? µp??e? ?a ??e? t?? e??? ?atast?se??

7
?ef??a?? 15 ??a?e???s? S??a??a???
?atast?se?? S??a??a???

• ??e??? (active) ?at?stas?
• ? s??a??a?? e?s???eta? st?? e?e??? ?at?stas? ?at?
  t?? a??? t?? epe?e??as?a? t?? ?a? pa?aµ??e? se
  a?t? e??s? e?te?e?ta?.
• ?at?stas? ?e????? ??sµe?s?? (partial commit)
• ? s??a??a?? ?e??e?ta? µe????? desµe?µ??? ?ta?
  ??e? ?????????e? ?a? ? te?e?ta?a e?t??? t??
  s??a??a???.
• ?at?stas? ?p?t???a? (failed)
• ? s??a??a?? ap?t?????e? ?ta? t? S??? a?t???f?e?
  ?t? de? µp??e? ?a s??e??se? t?? ?µa?? epe?e??as?a
  t??

8
?ef??a?? 15 ??a?e???s? S??a??a???
?atast?se?? S??a??a???

• ?at?stas? ?p??????? (aborted)
• ? s??a??a?? ß??s?eta? st?? ?at?stas? a?t? ?ta? ta
  ded?µ??a ????? epa????e? st?? p??????µe?? sta?e??
  ?at?stas?, p??? t?? a??? t?? e?t??es?? t??
  s??a??a???.
• st?? ?at?stas? ap??????? t? S??? ??e? d??
  ep?????? (a) t?? epa?e?????s? t?? s??a??a???
  ap? t?? a??? ? (ß) t?? ?atast??f? t??
  s??a??a???.
• ?at?stas? ??sµe?s?? (committed)
• ? s??a??a?? ??e? ????????se? ep?t???? t??
  e?t??es? t??.

9
?ef??a?? 15 ??a?e???s? S??a??a???
?d??t?te? S??a??a??? (ACID)

• ?t?µ???t?ta (atomicity)
• a? ?p???e? ?st? ?a? µ?a e?t??? t?? s??a??a???, ?
  ?p??a ap?t?????e? ?a e?te?es?e?, t?te ???????? ?
  s??a??a?? ap?t?????e? ep?s??.
• ?p?µ???s? (isolation)
• ???e s??a??a?? p??pe? ?a e?te?e?ta? a?e???t?ta
  ap? ???e? s??a??a???
• ????µ?t?ta (durability)
• a? µ?a s??a??a?? ?????????e? µe ep?t???a, t?te ??
  a??a??? p?? ??e? ep?f??e? ?ata???f??ta? µ???µa
  st? ?? ?a? de? µp????? ?a a?a???????.

10
?ef??a?? 15 ??a?e???s? S??a??a???
?d??t?te? S??a??a??? (ACID)

• S???pe?a (consistency)
• ? s??a??a?? p??pe? ?a µetat??pe? t? ß?s?
  ded?µ???? ap? µ?a s??ep? ?at?stas? se µ?a ????
  s??ep? ?at?stas? (ta ded?µ??a p??pe? ?a e??a?
  ????).
• ?? µ??a??sµ?? a?e?a??t?ta? ded?µ???? de? epa?????
  ??a t?? e????s? t?? s???pe?a?.
• Te??e?ste t? µetaf??? e??? p?s?? ap? ??a?
  t?ape???? ???a??asµ? se ?????. ? afa??es? t??
  p?s?? ap? t?? p??t? p??pe? ?a s???de?eta? ap? t??
  p??s?es? t?? p?s?? st? de?te??. ?? t? afa????µe??
  p?s? d?af??e? ap? t? p??st???µe??, t?te ta
  ded?µ??a t?? ß?s?? de? ????? s???pe?a (de? e??a?
  ????).

11
?ef??a?? 15 ??a?e???s? S??a??a???
???p?? epe?e??as?a?

• ????????a?? ? se???a?? e?t??es?
• ?p?? ?? s??a??a??? e?te????ta? ? µ?a µet? t??
  ???? a??? eµfa?????ta? s?µa?t???? ?a??ste??se??
  µe ap?t??esµa ?a µe???eta? ? ?e???? ap?d?s? t??
  s?st?µat??.
• ?a?t?????? e?t??es? p????? s??a??a???
• ?p?? ? d?s??? ? ? CPU µp????? ?a apas??????ta? µe
  ???? s??a??a??, ?p?te a????eta? ? a???µ?? t??
  s??a??a??? p?? ???????????ta? st? µ???da t??
  ?????? (throughput).
• ??e????t?µa µe?????ta? ?? ?a??ste??se?? (waiting
  time) ?a? ? µ?s?? ?????? e?t??es?? t?? s??a??a???
  (mean response time).
• ?e?????t?µa e?d??eta? ?a ep?f??e? p??ß??µata
  st?? a?e?a??t?ta ?a? s???pe?a t?? ded?µ???? t??
  ??.

12
?ef??a?? 15 ??a?e???s? S??a??a???
??e???? ta?t??????sµ??

• ? s?st?? s??t???sµ?? t?? s??a??a??? e??a? e?????
  t?? S???, t? ?p??? µ?s? t?? µ??a??sµ?? e??????
  ta?t??????sµ?? e????ta? t?? ?µa?? e?t??es? t??
  s??a??a???.
• ? t??p?? s??t???sµ?? ?a? e?t??es?? e??? s??????
  s??a??a??? ?a?e?ta? ?????d????aµµa (schedule).
• ?? S??? p??pe? ?a ep????e? ??a ?????d????aµµa p??
  ?a ??a??p??e? t?? apa?t?se?? s???pe?a? t??
  ded?µ????.

13
?ef??a?? 15 ??a?e???s? S??a??a???
?a?ade??µata ?????d?a??aµµ?t??
14
?ef??a?? 15 ??a?e???s? S??a??a???
Se???a?? ?????d????aµµa

• Se ??a se???a?? (serial) ?????d????aµµa ??
  e?t???? µ?a? s??a??a??? de? pe??p?????ta? ???????
  µe e?t???? t?? ????? s??a??a???.

15
?ef??a?? 15 ??a?e???s? S??a??a???
Se???a?? ?????d????aµµa

• ?p?????? n! d??at? se???a?? ?????d?a???µµata
  e?t??es?? ??a n s??a??a???.
• ? t??p?? e?t??es?? t?? s??a??a??? ????eta? ap? t?
  µ???d? ?????d??µ?????s?? p?? ???s?µ?p??e? t?
  ?e?t??????? s?st?µa ?a? ep?µ???? de? µp????µe ?a
  ????????µe µe a???ße?a t? ????? e?t??es?? t??
  ???e e?t???? µ?a? s??a??a???.

16
?ef??a?? 15 ??a?e???s? S??a??a???
Se????p???s?

• G?a ?a d?at??e? t? s???pe?a t?? ded?µ???? t?? ??
  ?a p??pe? t? ?????d????aµµa e?t??es?? s??a??a???
  ?a e??a? ?s?d??aµ? µe ??p??? se???a??
  ?????d????aµµa.
• ??? ?????d?a???µµata ?a????ta? ?s?d??aµa a? µet?
  t?? e?t??es? t??? ep?f????? t?? ?d?e? a??a??? st?
  ??.
• ? pa?a???? e??? ?????d?a???µµat?? ?s?d??aµ?? µe
  ??a se???a?? ?????d????aµµa ?a?e?ta? se????p???s?
  (serializability) ?a? ??e? d?? µ??f??
• se????p???s? s??????s?? (conflict), ?a?
• se????p???s? ???? (view).

17
?ef??a?? 15 ??a?e???s? S??a??a???
Se????p???s? s??????s??

• ?st? ?????d????aµµa S ?a? d?? ??????? s??e??µe?e?
  e?t???? Ei, Ej (p?? a?af????ta? sta ?d?a
  ded?µ??a D) t?? s??a??a??? S1, S2, a?t?st?????.
• ??a??????µe t?? e??? pe??pt?se??
• Ei read(D) ?a? Ej read(D)
• Ei read(D) ?a? Ej write(D)
• Ei write(D) ?a? Ej read(D)
• Ei write(D) ?a? Ej write(D)
• ?? t??????st?? µ?a e?t??? e??a? e?t???
  ap????e?s??, t?te ?? e?t???? Ei ?a? Ej ß??s???ta?
  se s??????s?

18
?ef??a?? 15 ??a?e???s? S??a??a???
Se????p???s? s??????s??

• ?? ??a ?????d????aµµa e?t??es?? S µp??e? ?a
  µetas??µat?s?e? se ??a ???? ?????d????aµµa S'
  a???-???ta? t? se??? e?t??es?? t?? e?t????, t?te
  ta S ?a? S' ?a????ta? ?s?d??aµa ?? p??? t??
  s??????se??.
• ?? ?????d????aµµa S ?a?e?ta? se????p???s?µ? ??
  p??? t?? s??????se?? (conflict serializable) a?
  e??a? ?s?d??aµ? ?? p??? t?? s??????se?? µe ??a
  se???a?? ?????d????aµµa.

19
?ef??a?? 15 ??a?e???s? S??a??a???
Se????p???s? s??????s?? ?a??de??µa
20
?ef??a?? 15 ??a?e???s? S??a??a???
Se????p???s? s??????s?? ??t?pa??de??µa
21
?ef??a?? 15 ??a?e???s? S??a??a???
Se????p???s? ????

• ?st? d?? ?????d?a???µµata S ?a? S? µe ta ?d?a
  s????a s??a??a???. ?a S ?a? S? ???µ????ta?
  ?s?d??aµa a? ??a ???e st???e?? ded?µ???? D
• a? ? s??a??a?? Si d?aß??e? t?? a????? t?µ? t?? D
  st? ?????-d????aµµa S, t?te p??pe? ? s??a??a?? Si
  ep?s?? ?a d?aß??e? t?? a????? t?µ? t?? D st?
  ?????d????aµµa S?,
• a? ? s??a??a?? Si e?te?e? t?? e?t??? Read(D) st?
  ?????d??-??aµµa S ?a? a?t? ? t?µ? ??e? pa?a??e?
  ap? t? s??a??a?? Sj, t?te ? Si p??pe? ep?s?? ?a
  d?aß?se? t?? t?µ? p?? pa???e? ? Sj st?
  ?????d????aµµa S?,
• ? s??a??a?? p?? e?te?e? t?? te?e?ta?a e?t???
  Write(D) st? ?????d????aµµa S, p??pe? ?a? st?
  ?????d????aµµa S' ?a e?te?e? t?? te?e?ta?a
  e?t??? Write(D).

22
?ef??a?? 15 ??a?e???s? S??a??a???
Se????p???s? ????

• ??a ?????d????aµµa S ?a?e?ta? se????p???s?µ? ??
  p??? t?? ??? (view serializable) a? e??a?
  ?s?d??aµ? ?? p??? t?? ??? µe ??p??? se???a??
  ?????d????aµµa.

23
?ef??a?? 15 ??a?e???s? S??a??a???
???a??sµ?? ??e?d?µat??

• ? ??e?da??? (lock) a?t?st???e? se ??a tµ?µa
  ded?µ???? ?a? e??a? µetaß??t? p?? pe?????fe? t??
  ?at?stas? t?? tµ?µat?? t?? ded?µ???? se s??s? µe
  t?? ?e?t?????e? p?? e?e????? sta s???e???µ??a
  ded?µ??a.

24
?ef??a?? 15 ??a?e???s? S??a??a???
???a??sµ?? ??e?d?µat??

• ??? e??a? ?? ßas???? t?p?? ??e?da????
• ??e?da??? a?????s?? (read) ? ??e?da???
  d?aµ???asµ?? (share), p?? ep?t??pe? se µ?a
  s??a??a?? ?a d?aß?se? ta ded?µ??a a??? ??? ?a ta
  e??µe??se? ? ?a ta d?a????e?,
• ??e?da??? ap????e?s?? (write) ? ap???e?st???
  ??e?da??? (exclusive), p?? ep?t??pe? se µ?a
  s??a??a?? ?a d?aß?se? ? ?a e??µe??se? ta
  ded?µ??a.

25
?ef??a?? 15 ??a?e???s? S??a??a???
???a??sµ?? ??e?d?µat?? ?

• ? µ??a??sµ?? ??e?da???? ?e?t????e? ?? e???
• µ?a s??a??a?? p?? af??? a?????s? ded?µ????, ??t?
  ?a t?? ???????e? µ?a ??e?da??? a?????s??,
• a? apa?te?ta? e??µ???s? ded?µ????, t?te ??t? µ?a
  ??e?da??? ap????e?s??,
• a? de? ?p???e? ???? ??e?da??? ??a t? s???e???µ???
  se??da ded?µ????, t?te ? ??e?da??? ?????e?ta? st?
  s??a??a??,
• a? ?p???e? ?d? ???? ??e?da??? p?? ??e? ???????e?
  se ???? s??a??a??, t?te p?a?µat?p??e?ta? ??e????
  ??a t? a? ?a ???????e? ? ??e?da??? st? ??a
  s??a??a?? ? ???.

26
?ef??a?? 15 ??a?e???s? S??a??a???
???a??sµ?? ??e?d?µat?? ??

• a? ? se??da ded?µ???? ??e? ??e?d??e? µe ???s?
  ??e?da???? a?????s?? ?a? ? ??a s??a??a?? ??t?
  ep?s?? ??e?da??? a?????s??, t?te t? s?st?µa
  ep?t??pe? t? ??????s? t?? ??e?da????.
• Se d?af??et??? pe??pt?s? ? ??a s??a??a?? p??pe?
  ?a pe??µ??e? µ???? ? p??????µe?? s??a??a??
  ????????se? t?? e??as?a µe t? se??da ded?µ????
  ?a? ape?e??e??se? t?? ??e?da???.
• µ?a s??a??a?? ape?e??e???e? t?? ??e?da??? ?ta? ?
  e?t??es? t?? ?????????e? e?te µe ep?t???a e?te µe
  ap?t???a.
• ?? µ???µe? a??a??? sta ded?µ??a e??a? ??at?? ap?
  t?? ?p????pe? s??a??a??? µ??? µet? t??
  ape?e?????s? t?? ??e?da???? ap????e?s?? ap? t?
  s??a??a??.

27
?ef??a?? 15 ??a?e???s? S??a??a???
???a??sµ?? ??e?d?µat?? ???

• µ?a s??a??a?? p?? p??pe? ?a e??µe??se? ??p??a
  ded?µ??a µp??e? ?a ??t?se? a?aß??µ?s? (upgrade)
  t?? ??e?da???? ap? ??e?da??? a?????s?? se
  ??e?da??? ap????e?s??.
• a? ? e???af? t?? ded?µ???? ??e? ?????????e? a???
  ? s??a??a?? de? ??e? ????????se? t?? a?????s? t??
  ded?µ????, t?te µp??e? ?a ??t?se? ?p?ß??µ?s?
  (downgrade) t?? ??e?da???? ap? ap????e?s?? se
  a?????s??.

28
?ef??a?? 15 ??a?e???s? S??a??a???
???a??sµ?? ??e?d?µat?? ??t?pa??de??µa
29
?ef??a?? 15 ??a?e???s? S??a??a???
???t?????? ??e?d?µat??

• ??a? µ??a??sµ?? ??e?d?µat?? p??pe? ?a ??a??p??e?
  ?a???e? e????s?? t?? s???pe?a? t?? ded?µ????.
• ?? ?a???e? a?t?? ??????? ??a p??t??????
  ??e?d?µat?? (locking protocol) ?a? e?????ta? ?t?
  t? ?????d????aµµa p?? p????pte? e??a?
  se????p???s?µ?.
• ???t?????? ??e?d?µat?? ??? F?se?? (two-phase
  locking)
• f?s? a??pt???? (growing phase), ?p?? ? s??a??a??
  ??t? t? ??????s? ??e?da???? ?a? de? ep?t??peta? ?
  ape?e?????s? ??e?da????,
• f?s? s???????s?? (shrinking phase), ?p?? ?
  s??a??a?? ape?e??e???e? ??e?da???? ?a? de?
  ep?t??peta? ?a ??t?se? t? ??????s? ????
  ??e?da????.

30
?ef??a?? 15 ??a?e???s? S??a??a???
???t?????? ??e?d?µat?? d?? f?se??
31
?ef??a?? 15 ??a?e???s? S??a??a???
???t?????? ??e?d?µat?? d?? f?se??
32
?ef??a?? 15 ??a?e???s? S??a??a???
???t?????? ??e?d?µat?? ßas?sµ??? se ???f?

• ?ta? e??a? ???st? ? se??? p??spe??se?? t??
  ded?µ???? ap? t? s??a??a?? ???s?µ?p??e?ta? t?
  p??t?????? ??e?d?µat?? ßas?sµ??? se ???f?.
• ?st? Dd1,d2,,dn ??a s????? n ded?µ???? p??
  p??spe?a????ta? ap? t?? s??a??a??? e?te ??a
  a?????s? e?te ??a ap????e?s?.
• ??????µe µ?a µe???? d??ta?? st? s????? D ?? e???
  
• ta ded?µ??a di ?a? dj s??d???ta? µe t? s??s? ? a?
  ???e s??a??a?? p?? p??spe?a??e? ta di ?a? dj
  p??spe?a??e? t? di p??? ap? t? dj.
• ? µe???? d??ta?? ep?t??pe? t?? a?apa??stas? t??
  s?????? ?? ?ate?????µe?? ?????? ???f? (dag).

33
?ef??a?? 15 ??a?e???s? S??a??a???
???t?????? ??e?d?µat?? ßas?sµ??? se ???f?

• ??d??? pe??pt?s? t?? ?ate?????µe??? ???????
  ???f?? e??a? ? de?d????? ???f??, ?p?? efa?µ??eta?
  t? de?d???? p??t?????? (tree protocol) p??
  ?p?st????e? µ??? ??e?da???? a?????s??.

34
?ef??a?? 15 ??a?e???s? S??a??a???
?e?d???? p??t??????

• ?? de?d???? p??t?????? ??e? t??? e??? ?a???e?
• ? ???e s??a??a?? µp??e? ?a ??t?se? ??????s? t??
  p??t?? ??e?da???? se ?p???d?p?te ded?µ???,
• µ?a s??a??a?? µp??e? ?a ??t?se? t? ??????s?
  ??e?da???? st? ded?µ??? dj µ??? a? ??e? ?d?
  ??e?d?se? t? ded?µ??? di ?a? ?s??e? di ? dj
• µ?a s??a??a?? µp??e? ?a ape?e??e??se? µ?a
  ??e?da??? ?p??ad?p?te ??????? st??µ?,
• ??a ded?µ??? p?? ??e? ??e?d??e? ap? µ?a s??a??a??
  ?a? st? s????e?a ? ??e?da??? ??e? ape?e??e???e?,
  de? ep?t??peta? ?a ??e?d??e? ??a de?te?? f??? ap?
  t? ?d?a s??a??a??.

35
?ef??a?? 15 ??a?e???s? S??a??a???
?e?d???? p??t??????

• ?a??de??µa pa?aß?as?? t?? 2?? ?a???a

36
?ef??a?? 15 ??a?e???s? S??a??a???
??a?e???s? ad?e??d??

• ??a s????? s??a??a??? ß??s?eta? se ad????d?
  (deadlock), ?ta? ?aµ?a s??a??a?? de? e??a? ef??t?
  ?a s??e??se? t?? e?t??es? t??, ???? a?aµ???? ??a
  t?? ape?e?????s? ??e?da????.
• ?? ad????d? ap?te?e? pa???????? ?at?stas? ?a?
  p??pe? ?a ap?fe??eta?.

37
?ef??a?? 15 ??a?e???s? S??a??a???
??a?e???s? ad?e??d??

• ? d?a?e???s? t?? ad?e??d?? p?a?µat?p??e?ta?
  ?e???? µe d?? µe??d???
• ap?f??? ad?e??d?? (deadlock prevention), ?p?? t?
  s?st?µa e????e? t?? p??a??t?ta ?a s?µße? ad????d?
  ?a? p??spa?e? ?a t? ap?f??e? (p??te??eta? ?ta?
  s?µßa????? p???? ad????da),
• a?a?????s? ad?e??d?? ?a? epa???t?s? (deadlock
  detection and recovery) ?p?? t? s?st?µa e??a? se
  ??s? ?a a?a?????se? ??a ad????d? ?a? p??ßa??e? se
  e????e?e? ??a t?? ?at????s? t?? (p??te??eta? ?ta?
  de? s?µßa????? p???? ad????da).

38
?ef??a?? 15 ??a?e???s? S??a??a???
?p?f??? ad?e??d??

• ??a µ???d?? ap?f???? t?? ad?e??d?? e??a? ?
  ???sµ?? e??? µ???st?? ???????? d?ast?µat?? ??a
  t?? a?aµ??? ??????s?? µ?a? ??e?da????.
• ?? e?a?t???e? t? ??????? d??st?µa ?a? ? ??e?da???
  de? ??e? a??µ? ???????e? st? s??a??a??, t?
  s?st?µa te?µat??e? t? d?ad??as?a ?a? t??
  epa?ad?µ?????e?.
• ? µ???d?? a?t? ap?f???? ad?e??d?? ???s?µ?p??e?ta?
  ap? p???? S??? ???? t?? ap??t?t?? t??.

39
?ef??a?? 15 ??a?e???s? S??a??a???
?p?f??? ad?e??d??

• ??a ???? µ???d?? e??a? a?t? t?? ????????
  sf?a??d?? (timestamps) ?a? p??te????ta? d??
  a??????µ??
• Wait-Die, p?? ep?t??pe? se µ?a pa?a??te??
  s??a??a?? (µ???? ??????? sf?a??da) ?a pe??µ??e?
  t?? ape?e?????s? µ?a? ??e?da???? ap? µ?a ?e?te??
  (µe?a??te?? ??????? sf?a??da). ??af??et???,?
  s??a??a?? te?µat??eta? ?a? t? s?st?µa t??
  epa?e????e?.
• Wound-Wait, ?p?? ep?t??peta? se µ?a ?e?te??
  s??a??a?? ?a pe??µ??e? t?? e?t??es? µ?a?
  pa?a??te???. ?? ? pa?a??te?? s??a??a?? ??t? t?
  ??????s? µ?a? ??e?da???? p?? e??a? desµe?µ??? ap?
  µ?a ?e?te?? s??a??a??,t?te ? ?e?te?? s??a??a??
  te?µat??eta?.

40
?ef??a?? 15 ??a?e???s? S??a??a???
??a?????s? ?a? ?at????s? ad?e??d??

• ? a?a?????s? ad?e??d?? se ??a s????? s??a??a???
  d?ap?st??eta? µe t? ß???e?a e??? ?ate?????µe???
  ???f?? p?? ?a?e?ta? ???f?? a?aµ???? (wait graph)
• ? ???f?? a?t?? ap?te?e?ta? ap? ??a s????? ????f??
  V ?a? ??a s????? a?µ?? E. G?a ???e s??a??a??
  ?p???e? ?a? µ?a a?t?st???? ????f? st? ???f?.
• ?? ?p???e? a?µ? ap? t?? ????f? Si p??? t??
  ????f? Sj, t?te a?t? d????e? ?t? ? s??a??a?? Si
  a?aµ??e? µ???? ? s??a??a?? Sj ?a ape?e??e??se?
  t?? ??e?da??? se ??a tµ?µa ded?µ???? p?? p??pe?
  ?a p??spe??se? ? Si.

41
?ef??a?? 15 ??a?e???s? S??a??a???
??a?????s? ?a? ?at????s? ad?e??d??

• ?? st? ???f? a?aµ???? de? ?p???e? ??????, t?te
  de? ?p???e? ad????d?. ??t??eta, ? ?pa??? ?st? ?a?
  e??? ?????? s?µa??e? ?t? ??a ?p?s????? t??
  s??a??a??? ß??s?eta? se ad????d?.
• ?? s?µßa????? s???? ad????da p??pe? ?a e??a?
  s????? ?a? ? ??e???? t?? ???f?? a?aµ????.
• ?? S??? µp??e? ?a d?at??e? stat?st??? st???e?a
  ??a t?? a???µ? t?? ad?e??d?? ?a? t? s????t?ta
  eµf???s?? t??? ?a? a?????a ?a p??sd?????eta? ?a?
  ? s????t?ta t?? e?????? ??a ad????d?.

42
?ef??a?? 15 ??a?e???s? S??a??a???
??a?????s? ?a? ?at????s? ad?e??d??
43
?ef??a?? 15 ??a?e???s? S??a??a???
?at????s? ad?e??d??

• ? s????te?a ???s?µ?p????µe?? µ???d?? ??a t??
  ?at????s? t?? ad????d?? e??a? ? te?µat?sµ?? µ?a?
  ? pe??ss?t???? s??a??a??? ?a? ? epa?af??? t??
  ded?µ???? st?? ?at?stas? p?? ß??s??ta? p??? ap?
  t?? e?t??es? t?? s??a??a??? a?t?? (ROLLBACK).

44
?ef??a?? 15 ??a?e???s? S??a??a???
?at????s? ad?e??d??

• ? µ???d?? ROLLABACK e?te?e?ta? ?? e???
• ??µa 1. ?p????? s??a??a??? ??a ROLLABACK. H
  ep????? t?? s??a??a??? p?a?µat?p??e?ta? µe ß?s?
  t? e????st? ??st??. S?µf??a µe t??? e???
  pa?????te?
• ? µ???? st??µ?? ?????? e?t??es?? t?? s??a??a???
  ?a? ? ?p??e?p?µe??? ?????? ??a t?? ????????s? t??
  s??a??a???,
• ? a???µ?? t?? ded?µ???? p?? ????? e??µe???e? ap?
  t? s??a??a??,
• ? a???µ?? t?? ded?µ???? p?? p??pe? ?a
  p??spe?as???? ap? t? s??a??a??,
• ? a???µ?? t?? s??a??a??? ?p?? ?a efa?µ?s?e? ?
  ?e?t?????a ROLLBACK.

45
?ef??a?? 15 ??a?e???s? S??a??a???
?at????s? ad?e??d??

• ??µa 2. ?p????? s?µe??? ROLLBACK.
• ? ap???ste?? ??s? e??a? ?a ???e? epa?af??? t??
  s??a??a??? st?? a???, ?ata????ta? ??e? t??
  a??a??? p?? ??e? ep?f??e? sta ded?µ??a,
• ? ??s? a?t? ??e? µe???? ??st??, d??t? ? s??a??a??
  µp??e? ?a ??e? e??µe??se? ??a µe???? a???µ?
  ded?µ????,
• s??????, t? ad????d? ?ata??e?ta? efa?µ????ta?
  ROLLBACK st?? te?e?ta?e? e?t???? t?? s??a??a???.

46
?ef??a?? 15 ??a?e???s? S??a??a???
?at????s? ad?e??d??

• ??µa 3. ?p?f??? at??µ???? a?aµ????.
• ? at??µ??? a?aµ??? (starvation) e??a? ??a
  fa???µe?? p?? µp??e? ?a eµfa??s?e? a? ep????eta?
  s??e??? ? ?d?a s??a??a?? ??a t?? efa?µ??? t??
  ROLLBACK,
• a?t? s?µa??e? ?t? s??e??? ? ?d?a s??a??a??
  eµp?d??eta? ?a ????????se? t?? e?t??es? t??,
• t? S??? µp??e? ?a ap?t???e? t?? ep????? t?? ?d?a?
  s??a??a??? pe??ss?te?? ap? ??a? a???µ? ep??????,
  d????ta? ?ts? t?? e??a???a st? s??a??a?? ?a
  ????????se? t?? epe?e??as?a t??.

47
?ef??a?? 15 ??a?e???s? S??a??a???
???a??sµ?? ???????? sf?a??d??

• ? µ??a??sµ?? ???????? sf?a??d?? de? ???s?µ?p??e?
  ??e?da???? ??a t?? p??stas?a µ?a? pe??????
  ded?µ????, ??a de? ?p???e? pe??pt?s? ?a
  d?µ???????e? ad????d?.
• ? ??????? sf?a??da e??a? µ?a µetaß??t? p??
  p??sd??-???e? t? ??????? st??µ? t?? a???? t??
  e?t??es?? µ?a? s??a??a???.
• ??a ??????? sf?a??da pa???eta? e?te ap? t? ?????
  t?? s?st?µat?? e?te e??µe?????ta? t?? t?µ? µ?a?
  µetaß??-t?? ???e f??? p?? d?µ?????e?ta? µ?a ??a
  s??a??a??.
• ? ??????? sf?a??da t?? s??a??a??? Si s?µß????eta?
  µe TS(Si).

48
?ef??a?? 15 ??a?e???s? S??a??a???
???a??sµ?? ???????? sf?a??d??

• ? p??sp??as? ep?t??peta? µ??? a? ? te?e?ta?a
  e??µ?-??s? p?a?µat?p??????e ap? pa?a??te??
  s??a??a?? (p?? ?a ??e? µ????te?? ???????
  sf?a??da).
• ?????? p?a?µat?p??e?ta? te?µat?sµ?? ?a?
  epa?e?????s? t?? s??a??a??? µe ??a ???????
  sf?a??da.
• ???????? sf?a??de? ??????ta? ??? µ??? ??a t??
  s??a??a-??? a??? ?a? ??a ta ded?µ??a
• se ???e se??da ded?µ???? a?t?st???e? µ?a ???????
  sf?a??da a?????s?? ?a? µ?a ??????? sf?a??da
  ap????e?s??,
• ?? d?? ???????? sf?a??de? s?µß??????ta? µe
  timestamp-W ?a? timestamp-R a?t?st???a.

49
?ef??a?? 15 ??a?e???s? S??a??a???
???a??sµ?? ???????? sf?a??d??

• ? t?µ? t?? ???????? sf?a??da? a?????s?? e??a? ?
  t?µ? t?? ???????? sf?a??da? t?? s??a??a??? p??
  p?a?µat?p???se te?e?ta?a a?????s? st? se??da
  ded?µ????.
• ? t?µ? t?? ???????? sf?a??da? ap????e?s?? e??a?
  ? ??????? sf?a??da t?? s??a??a??? p??
  p?a?µat?p???se te?e?ta?a e??µ???s? st? se??da
  ded?µ????.
• ???e f??? p?? p?a?µat?p??e?ta? a?????s? ?
  ap???-?e?s? t?? se??da? ded?µ???? D,
  e??µe?????ta? ?? t?µ?? timestamp-W(D) ?a?
  timestamp-R(D), a?t?st?????.

50
?ef??a?? 15 ??a?e???s? S??a??a???
???t?????? d??ta??? ???????? sf?a??d??
51
?ef??a?? 15 ??a?e???s? S??a??a???
???t?????? d??ta??? ???????? sf?a??d??
52
?ef??a?? 15 ??a?e???s? S??a??a???
?a???a? ap????e?s?? t?? Thomas

• ?e t? ???s? t?? µe??d?? t?? ???????? sf?a??d?? a?
  µ?a s??a??a?? p??spa??se? ?a a????e? t?? t?µ?
  µ?a? se??da? ded?µ????, ? ?p??a ??e? ?d?
  e??µe???e? ap? ???? s??a??a??, t?te ? e?t??es?
  t?? s??a??a??? d?a??pteta? ?a? p?a?µat?p??e?ta?
  ROLLBACK.
• S?µf??a µe t?? ?a???a ap????e?s?? t?? Thomas
  a??e? ?a a????s??µe t? ?e?t?????a ap????e?s??,
  ?p?te
• µe???eta? t? ??st?? ?e?t?????a?, ?a?
• a????eta? ? ap?d?s? t?? s?st?µat??.

53
?ef??a?? 15 ??a?e???s? S??a??a???
?a???a? ap????e?s?? t?? Thomas
54
?ef??a?? 15 ??a?e???s? S??a??a???
?a???a? ap????e?s?? t?? Thomas

• ?? ??? p??t?????? d?af??e? µ??? ?? p??? t?
  d?a?e???s? t?? e?t???? ap????e?s??
• a? TS(Si) lt timestamp-W(D), t?te ? s??a??a??
  p??spa?e? ?a e??µe??se? µ?a t?µ? p?? ??e? ?d?
  a????e? ap? ???? s??a??a??. St?? pe??pt?s? a?t? ?
  e?t??? ap????e?s?? µp??e? ?a a?????e? µe
  asf??e?a.
• a? TS(Si) lt timestamp-R(D),
• t?te ? t?????sa t?µ? t?? D d?aß?s???e
  p??????µ???? ap? ???? s??a??a??. St?? pe??pt?s?
  a?t? d?a??pteta? ? e?t??? ap????e?s?? ?a?
  p?a?µat?p??e?ta? ROLLBACK.
• a? de? ?s??e? ?aµ?a ap? t?? d?? s?????e?,
• t?te ? ?e?t?????a ap????e?s?? µp??e? ?a
  ?????????e? ????? p??ß??µa ?a? timestamp-W(D)
  TS(Si).

55
?ef??a?? 15 ??a?e???s? S??a??a???
?pa???t?s? ded?µ????

• ?? s????te?e? a?t?e? p?? ?d????? se d?a??p? t??
  ?e?t?????a? t?? s?st?µat?? e??a?
• pt?s? s?st?µat??, ???? esfa?µ???? ?e?t?????a? t??
  ?????? ? t?? ????sµ???? s?st?µat??,
• p??ß??µa st? µ?s? ap????e?s??, t? ?p??? µp??e? ?a
  ?fe??eta? se ?atast??f? t?? µa???t???? ep?f??e?a?
  t?? d?s???, t?? µ??a????? ? t?? ??e?t???????
  ?????? t?? d?s???,
• sf??µa ????sµ???? efa?µ????, t? ?p??? ?fe??eta?
  s?????? se sf??µa e?t??es?? (run-time error) ?at?
  t? d????e?a e??µ???s?? t?? ded?µ???? t?? ??,
• f?s??? a?t?a, ?p?? p???a????, se?sµ?? ??p.

56
?ef??a?? 15 ??a?e???s? S??a??a???
?pa?t?se?? epa???t?s?? ded?µ????

• G?a ?a e??a? ef??t? ? ?e?t?????a t?? epa???t?s??
  ded?µ????, t? S??? p??pe? ?a d?a??te?
• µ??a??sµ? d?µ??????a? a?t????f?? asfa?e?a?
  (backup) ??a ta ded?µ??a t?? ??,
• ?ata??af? ?µe???????? (log) ?p?? ?a ap????e?eta?
  ? ?at?stas? t?? ???e s??a??a??? ?a? ?? a??a???
  p?? ????? p?a?µat?p????e? st? ??,
• µ??a??sµ? ???????? s?µe??? e?????? (checkpoints)
  p?? s?µat?d?t??? t?? st??µ?? p?? ?? a??a??? p??
  ????? ep?f??e? ?? s??a??a??? ????? ???e? µ???µe?,
• µ???d? epa???t?s??, ? ?p??a ?aµß????ta? ?p??? ta
  a?t???afa asfa?e?a?, t?? p????f???e? ?µe????????
  ?a? ta ??????? s?µe?a e??????, epa?af??e? t? ??
  se ?at?stas? s???pe?a?.