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functions.c

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    • Alvaro Herrera's avatar
      5da9da71
      Improve snapshot manager by keeping explicit track of snapshots. · 5da9da71
      Alvaro Herrera authored
      There are two ways to track a snapshot: there's the "registered" list, which
      is used for arbitrary long-lived snapshots; and there's the "active stack",
      which is used for the snapshot that is considered "active" at any time.
      This also allows users of snapshots to stop worrying about snapshot memory
      allocation and freeing, and about using PG_TRY blocks around ActiveSnapshot
      assignment.  This is all done automatically now.
      
      As a consequence, this allows us to reset MyProc->xmin when there are no
      more snapshots registered in the current backend, reducing the impact that
      long-running transactions have on VACUUM.
      5da9da71
      History
      Improve snapshot manager by keeping explicit track of snapshots.
      Alvaro Herrera authored
      There are two ways to track a snapshot: there's the "registered" list, which
      is used for arbitrary long-lived snapshots; and there's the "active stack",
      which is used for the snapshot that is considered "active" at any time.
      This also allows users of snapshots to stop worrying about snapshot memory
      allocation and freeing, and about using PG_TRY blocks around ActiveSnapshot
      assignment.  This is all done automatically now.
      
      As a consequence, this allows us to reset MyProc->xmin when there are no
      more snapshots registered in the current backend, reducing the impact that
      long-running transactions have on VACUUM.