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c.h

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    • Tom Lane's avatar
      295e6398
      Implement lazy XID allocation: transactions that do not modify any database · 295e6398
      Tom Lane authored
      rows will normally never obtain an XID at all.  We already did things this way
      for subtransactions, but this patch extends the concept to top-level
      transactions.  In applications where there are lots of short read-only
      transactions, this should improve performance noticeably; not so much from
      removal of the actual XID-assignments, as from reduction of overhead that's
      driven by the rate of XID consumption.  We add a concept of a "virtual
      transaction ID" so that active transactions can be uniquely identified even
      if they don't have a regular XID.  This is a much lighter-weight concept:
      uniqueness of VXIDs is only guaranteed over the short term, and no on-disk
      record is made about them.
      
      Florian Pflug, with some editorialization by Tom.
      295e6398
      History
      Implement lazy XID allocation: transactions that do not modify any database
      Tom Lane authored
      rows will normally never obtain an XID at all.  We already did things this way
      for subtransactions, but this patch extends the concept to top-level
      transactions.  In applications where there are lots of short read-only
      transactions, this should improve performance noticeably; not so much from
      removal of the actual XID-assignments, as from reduction of overhead that's
      driven by the rate of XID consumption.  We add a concept of a "virtual
      transaction ID" so that active transactions can be uniquely identified even
      if they don't have a regular XID.  This is a much lighter-weight concept:
      uniqueness of VXIDs is only guaranteed over the short term, and no on-disk
      record is made about them.
      
      Florian Pflug, with some editorialization by Tom.
    c.h 23.27 KiB