Ti copyback with tj reads because ti cant hurt tj but

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Unformatted text preview: hing Ti writes and Ti ends reading before Tj ends reading v r w v w • 3) Tj reads & writes nothing Ti writes and Ti ends reading before Tj ends reading r r v v w w – Overlap of Ti copyback with Tj reads because Ti can’t hurt Tj, but Tj might hurt Ti if its writes start too soon Simple testing of sets More parallelism • Long critical section if copyback slow • Test clearly preceding (no longer changing) transactions outside critical section Lock Unlock Even more parallelism • Add ordered testing of condition 3 Space issues • What if run out of space for sets? – Abort & retry • What about repeated abort & retry? – Hold critical section in a retry (ugh) Applic to B-trees • Models B-trees with lots of entries in each page (199), uniform key insertion, interior nodes cacheable and leaf pages not cacheable • Does consider splitting a leaf, but apparently not rotating tree to maintain balance (not needed if inserts are uniform :-) • Concludes for such B-trees that conflict, abort and restart will be rare (0.07%) Eval • Thought experiment – Not fair as really a database theory paper then • Analysis of B-tree not appropriate – Really should have modeled rotations as “randomness” is far too unlikely • Very influential: “optimistic methods” is current label of anything trying first then checking if it had a conflict and undoing it Lock-based Concurrency Control Client code BEGIN lookup • U...
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