so concurrent transactions sharing any page are

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Unformatted text preview: sed by most databases today – Inside any transaction, all accessed data is protected by read/write locks & stored in shadow pages or undo logs (later lecture) until changes are commited & written – All locks acquired are held until transaction is done (!) – So concurrent transactions sharing any page are serialized by page locks, that is, with respect to shared pages, execute one at a time – Beware deadlocks -- if locks cannot be hierarchicalized, then detect lock cycles and break with abort & rollback {client logic} lookup {logic} ... write END Speculative Execution • 300 15 Time (seconds) • synchronous RPCs, it can increase the latency of individual RPCs. Before a server can accept a file modification or grant a clien xclusive access o a fi , it mu t fi st syn Example:t eUnmodified tappsleusingsanrNFSchronously rev a y c b ks o l el b o e i Poservernoikelly,na wallll-cacnnectredealsiesnthmd st y aitthor clneents. more te t a eo ce uw n o or p oorl -conne ted c ent – Clientsycache cdata,libuts. Speculator would help hide the latency of these exp ensive op erations. Thus, we exp ect that – Forle systems tha,t NFSleases are calllbacks would see substanfi consistency use ops or al sync tial b enefit f c , Client-serversrotmaSptehatlasteorn evefilthsougems e haltauisvepboelniefit latencyugreatly n e yst hthings t e l ng. slows th t re would b e le s h n e by down Speculator also reduces the cost of providing safety guarante...
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This note was uploaded on 05/30/2013 for the course COMP SCI 15-812 taught by Professor Smith during the Spring '12 term at Carnegie Mellon.

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