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  8. 28 Apr, 2005 1 commit
    • Tom Lane's avatar
      Implement sharable row-level locks, and use them for foreign key references · bedb78d3
      Tom Lane authored
      to eliminate unnecessary deadlocks.  This commit adds SELECT ... FOR SHARE
      paralleling SELECT ... FOR UPDATE.  The implementation uses a new SLRU
      data structure (managed much like pg_subtrans) to represent multiple-
      transaction-ID sets.  When more than one transaction is holding a shared
      lock on a particular row, we create a MultiXactId representing that set
      of transactions and store its ID in the row's XMAX.  This scheme allows
      an effectively unlimited number of row locks, just as we did before,
      while not costing any extra overhead except when a shared lock actually
      has to be shared.   Still TODO: use the regular lock manager to control
      the grant order when multiple backends are waiting for a row lock.
      
      Alvaro Herrera and Tom Lane.
      bedb78d3