{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

Client logic lookup read several pages logic write

Info icon This preview shows page 1. Sign up to view the full content.

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

Unformatted text preview: hase • Doesn’t lock DB during client logic computation Client code BEGIN lookup DB/FS/etc. {client logic} lookup read several pages {logic} ... write END read several pages write shadow copy of pages Validate Write • Groups reads & writes of same blocks close in time • “Pre-fetches” blocks for validation/write phase Validation: Serializability • Separately test all transactions consistent – Running alone on database, transaction assumed correct • Make transaction codes independent of each other – Happens-before only property of (data) values in db • All serial orderings of “concurrent” transactions are valid • Allow concurrent running if transformations are same as transforms possible from a serial order – Serializable Tentative state Real state or rollback Basic approach: transaction IDs • Serializability means a serial ordering exists • Select ID for each transaction a priori – Force DB updates to be equivalent to serial execution in numeric order of ID values – In validation phase, abort & retry transactions that would not meet this condition • Transforms lock queueing slowdowns for the risk of not making progress – ID selected at “begin” less concurrent if some read phases run much longer – Delay ID choice until validation or later to reduce aborts Conditions for validity • 1) Ti ends copyback before Tj reads start r v w r • For i<j, Transaction Ti must “precede” Tj • 1) Ti ends copyback before Tj reads start, or v w • 2) Tj reads nothing Ti writes and Ti ends copyback before Tj starts copyback, or – Actually serial ordering r • 2) Tj reads nothing Ti writes and Ti ends copyback before Tj starts copyback, or – Overlap of Tj reading with Ti copyback is harmless & Tj copyback is serialized after Ti copyback • 3) Tj reads & writes not...
View Full Document

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern