Basic HTML version of Foils prepared 7 October 97

Foil 30 Consider the following PCM Example

From Second Part of RDBMS Discussion ARL Database Tutorial -- February 98. by Gang Cheng Marek Podgorny Chao-Wei Ou
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.

© on Mon Oct 13 1997