HELP! * GREY=local LOCAL HTML version of Foils prepared July 6,1995

Foil 32 Consider the following PCM Example

From Explicit Examples in Parallel Relational Databases CPS600 Spring Semester -- April 1995. by Gang Cheng Marek Podgorny (Geoffrey Fox) * See also color IMAGE
Time
  • 1 Instance X attempts to update row 1 in (data block n)
  • Instance X becomes owner of PCM lock for data block n
  • Instance X update row 1
  • 2 Instance Y attempts to update row 2 in (data block n)
  • Instance Y requests the PCM lock from instance X for data block n
  • Instance X releases the PCM lock
  • Instance Y becomes owner of PCM lock for data block n
  • Instance Y update row 2
  • 3 Instance X attempts to update row 3 in (data block n)
  • Instance X requests the PCM lock from instance Y for data block n
  • Instance Y releases the PCM lock
  • Instance X becomes owner of PCM lock for data block n
  • Instance X update row 3
The PCM is handled separately from transaction lock -- when instance wish to update the same data (e.g.: Instance X and Y attempt to update Row 1), normal transaction locking is involved.

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