{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

serial_update - SERIALIZABILITY P.MIRUNALINI AP,CSE SSNCE...

Info iconThis preview shows pages 1–10. Sign up to view the full content.

View Full Document Right Arrow Icon
SERIALIZABILITY P.MIRUNALINI AP,CSE SSNCE
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
OVERVIEW square6 Schedules square6 Conflict Operations square6 Characterizing schedules square6 Recoverable and non-recoverable schedules square6 Cascading rollback and cascadeless square6 Serializability of Schedules square6 Serial and non-serial schedules square6 Conflict serializability
Background image of page 2
Schedules square6 A schedule ( or history) S of n transactions T1, T2, .... , Tn is an ordering of the operations of the transactions subject to the constraint that: square6 For each transaction Ti that participates in S, the operation of Ti in S must appear in the same order in which they occur in Ti. square6 Sometimes, the operations from other transactions Tj can be interleaved with the operations of Ti in S.
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Schedules square6 Sa: r1(X); r2(X); w1(X); r1(Y); w2(X); c2; w1(Y); c1;
Background image of page 4
Schedules square6 Two operations in a schedule are said to conflict: square6 if they belong to different transactions square6 if they access the same item X square6 if one of the two operations is a write_item(X)
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Characterizing Schedules square6 Recoverable Schedule : square6 Once a transaction T is committed, it should never be necessary to roll back T. The schedules that meet this criteria are called recoverable schedules. square6 A schedule S is said to be recoverable if no transaction T in S commits until all transactions T' that have written an item that T reads have committed.
Background image of page 6
Recovery – Schedule square6 A schedule to be recoverable is as follows: square6 If A sees any of B's updates, then A must not commit before B terminates. square6 w2(t); r1(t); w1(t); c1; a2 unrecoverable schedule
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Characterizing Schedules Consider two schedules: Sc: r1 (X); w1 (X); r2 (X); r1(Y); w2 (X); c2; a1; Sd: r1 (X); w1 (X); r2(X); r1(Y); w2 (X); w1(Y); c1; c2; square6 a) Sd is recoverable square6 b) Sc is not recoverable, because T2 reads item X from T1, and then T2 commits before T1 commits. If T1 aborts after the C2; then the value of X that T2 read is no longer valid and T2 must be aborted after it had already committed ---> schedule not recoverable.
Background image of page 8
Characterizing Schedules square6 Cascadeless Schedule : An uncommitted transaction has to be rolled back because it read an item from a transaction that failed.
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 10
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}