Transactions and P2P Systems

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Transactions and P2P Systems

• F?t?p????? ?as??e???
• ??a?as?p????? ?????s???

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? ?????a t?? Transaction

• Transaction e??a? µ?a se??? ap? e????e?e?
  a?????s?? ?a? e???af?? a?t??e?µ???? µ?a? ß?s??
  ded?µ????
• ??e???? s??d??µ???t?ta? (Concurrency Control)
  ??te????ta? e?t???? ap? d?af??et??? transactions
  µe e?a??ass?µe?? t??p? (?????p????aµµa). ?
  ta?t?????? e?t??es? t?? transactions apa?te?
  ??e??? s??d??µ???t?ta?
• ACID properties ?p?????? 4 ?d??t?te? t??
  transactions p?? p??pe? ?a e?asfa???e? ??a DBMS
  ?ste ?a p??state???ta? ta ded?µ??a ap? ta?t??????
  ???s? ? ß??ß? t?? s?st?µat??

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ACID properties

• Atomicity e?te ???????????ta? ??e? ??
  e????e?e? e??? transaction
• e?te ?aµ?a (a?a?????ta? e????e?e? ?µ?te???
  transactions)
• Consistency d?at??e?ta? ? s???pe?a t?? ß?s??
  µet? t?? e?t??es?
• e??? transaction (?pe?????t?ta t?? ???st?
  t??
• DBMS)
• Isolation ?? e????e?e? e??? transaction de?
  ep??e????? ??a ???? ta?t?????a
  e?te???µe??? transaction (??e????
  s??d??µ???t?ta?)
• Durability ?ta? ep??????e? t? transaction ??
  a??a??? de? ?????ta? a??µa ?a? e??
  ?ata??e?se? t? s?st?µa (?ata???feta? t?
  ?st????? t?? ß?s??)

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??e???? s??d??µ???t?ta?

• ? ??e???? s??d??µ???t?ta? e?asfa???e? ?t?
• ??a DBMS ep?t??pe? t?? e?t??es? µ???
  se????p???s?µ?? ?a?
• epa?af??s?µ?? ?????p????aµµ?t??
• de? ?????ta? e????e?e? ????????µ????
  (ep?????µ????) transactions ?at?
• t?? a?a??es? e??ata?e?e?µµ???? transactions
• ? ??e???? s??d??µ???t?ta? ???p??e?ta? ap? t?
  DBMS
• ???s?µ?p????ta? ??a ap? ta p??t?????a
  ??e?d?µat??
• ???s?µ?p????ta? d??ta?? ?????s?µ??
• ???s?µ?p????ta? p?st?p???s? e??? transaction
• Ta ???µ?p???s??µe t? a?st??? ??e?d?µa 2 f?se??
  (strict 2PL)
• ??at? ap?fe??eta? t? fa???µe?? t?? cascading
  aborts

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???p???s? t?? e?????? s??d??µ???t?ta?

• Transaction Manager
• a?????p??e? t?? e?t??es? t??
• transaction
• e????e? ???????? t?? e?t??es?
• e??? transaction
• pa???e? t?? ap?f?se?? s?et??? µe t?
• commit, abort t?? transaction

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? ?????a t?? Distributed Transaction

• ????µe ?ata?eµ?µ??? DBMS
• To Distributed Transaction (DT) ?p?ß???eta? se
• ??p???? s???e???µ??? ??µß? t?? ?ata?eµ?µ????
• s?st?µat??
• G?a ?a ?????????e? a?t? t? DT, ? Transaction
  Manager
• t?? a?????? ??µß?? t? d?asp? se µ?a s??????
  ap? ??a ?
• pe??ss?te?a transactions p?? e?te????ta? se
  d?af??et?????
• ??µß???
• ??t? ta ep?µ????? transactions ?p?ß?????ta? st??
  Transaction
• Manager t?? ????? ??µß??
• ?pa?te?ta? ?ata?eµ?µ???? ??e???? s??d??µ???t?ta?

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???p???s? t?? ?ata?eµ?µ???? e??????
s??d??µ???t?ta?
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??t?µata st?? ???p???s? t?? ?ata?eµ?µ???? e??????
s??d??µ???t?ta?

• ?ata?eµ?µ???? ??e???? s??d??µ???t?ta? ?st? ?t?
  ???s?µ?p????µa? t? p??t?????? strict 2PL.
• ??? µp??e? ?a ???e? ? d?a?e???s? ??e?da???? p??
  e??a?
• ap????e?µ??e? se d?af??et???? t?p??es?e?
• To p??t?????? strict 2PL t?s? st??
  ?e?t????p???µ??? ?s? ?a?
• st?? ?ata?eµ?µ??? ??d?s? t?? d?µ?????e?
  deadlocks ?at? t??
• d????e?a e?t??es?? t?? transactions
• ??? µp????µe ?a a????e?s??µe ta deadlocks
• ?p?p????, p?? µp??e? ?a e?te?este? t? p??t??????
  a?t? p???
• ap? ??a P2P s?st?µa

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???p???s? transactions p??? ap? P2P Networks

• ACID over P2P Se ??a P2P network, ?? ??µß??
• µp????? ?a ap?t???????? µe ??a? ????? ???µ?
  ?a?
• ep?µ???? ta ded?µ??a t??? ?a µ?? µp????? ?a
• p??spe?ast???
• ???a? d?s???? ?a ?p???e? ????????µ??? s?st?µa
  p??
• ?a µp??e? ?a efa?µ??e? ??e? t?? ACID
  properties t??
• transactions, a?t???t?? t?? efa?µ????? ???
  ??a s?µe??
• ?e?t????p???µ??a

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???t?se?? ??a ?ata?eµ?µ??? ??e??? s??d??µ???t?ta?

• ?ata?eµ?µ??? strict 2PL µe a????e?s? deadlocks
• ?e? ?p?????? a?t???afa a?t??e?µ???? (replicas)
• ???e ??µß?? ??e? ta d??? t?? a?t??e?µe?a
• ???e ??µß?? e??a? ?pe?????? ??a t?? ??e?da????
  ??p????
• a?t??e?µ???? p?? e??a? ap????e?µ??? se a?t??
  t?? ??µß?
• (distributed locking)
• G?a ?a ap?f????µe ta deadlocks ?a? t? starvation
  a?at??eta?
• se ???e transaction µ?a p??te?a??t?ta ??a
  t?? e?t??es? t??
• (global timestamps)

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?e?µat?sµ?? Distributed Transaction

• Atomicity
• To s?µa?t??? ??µµ?t? sta DT e??a? t? st?d?? t??
  ????????s??. ??te ?a p??pe? ???? ?? s?µµet????te?
  ??µß?? t?? transaction ?a p????? µ?a e??a?a
  ap?fas?
• ??? de? p????? µ?a e??a?a ap?fas? t?te
  ?atapate?te ? ?d??t?ta t?? atomicity
• G?a ?a e?asfa??ste? ? atomicity ?p???e? µ?a
  p??????a p??t??????? p?? ????? p??ta?e?(distribute
  d commit protocol)

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Distributed Commit Protocols

• Three Phase Commit
• Two Phase Commit
• O ??µß?? p?? ?e????se t? transaction (master)
  µ???? t? ????????se? a?????p??e? t? p??t??????
  p?? ap?te?e?ta? ap? d?? f?se??
• 1? f?s? ? master st???e? µ???µa t?p?? PREPARE
  se ????? t???
• s?µµet????te? ??t??ta? t??? ??a t?? ??ßas?
  t?? transaction.
• ??t?? a?????a apa?t??? st???o?ta? st??
  master ??a µ???µa
• t?p?? VOTE YES ? VOTE NO
• 2? f?s? ? master µ???? ??ße? ????? t??? ??f???
  apa?t? ?? e???
• ??? ???? ??f?s??? VOTE YES ep??????e? t??
  s??a??a?? ?a?
• st??e? µ???µa t?p?? COMMIT. ??? ?st? ?a?
  ??a? ??f?se?
• VOTE NO st???e? µ???µa ABORT

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Distributed Commit Protocols
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?? a?aµ????µe-St????

• Te????ta? d?µ? da?t????? (structured p2p) st????
  µa? e??a? ?a d?s??µe µ?a a???te?t????? µ?s? t??
  ?p??a? ?a e?te????ta? ?ata?eµ?µ??e? s??a??a??? se
  p2p s?st?µata d?asfa?????ta? p??t?st?? t??
  ?d??t?te?
• Atomicity
• Isolation