27 november 5th 2012 cs480 principles of data

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Unformatted text preview: 5th, 2012 L23.24 4 2/11/13 CS480 Principles of Data Management Spring 2013 CS480 Principles of Data Management Spring 2013 What if many writers concurrently append? •  Append ­at ­least ­once semanIcs preserves each writer’s output Managing Mutations •  Each record contains extra informaIon like checksums so that its validity can be verified Handling writes and appends to a file –  Reader can idenIfy and discard extra padding 25 Colorado State University, Sangmi Pallickara 2/10/13 CS480 Principles of Data Management Spring 2013 GFS uses leases to maintain consistent mutation order across replicas CS480 Principles of Data Management Spring 2013 Lease mechanism designed to minimize communications with the master •  Lease has iniIal 8meout of 60 seconds •  Master grants lease to one of the replicas –  PRIMARY •  As long as chunk is being mutated –  Primary can request and receive extensions •  Primary picks serial ­order •  Extension requests/grants piggybacked over heart ­beat messages –  For all mutaIons to the chunk –  Other replicas follow this order •  When applying mutaIons L23.27 November 5th, 2012 CS480 Principles of Data Management L23.26 November 5...
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