generic LONG VARLENA

Well,

    first  I  want  to  summarize  some details, to see if we all
    agree so far in the discussion.

    - The implementation should be generic for all variable  size
      types, but can be enabled/disabled per type.

    - Large values are moved out of the main tuple until it fit's
      a yet to be defined size.

    - The moved off values  are  kept  in  another  relation  per
      table,  using  regular tuples where the value is split into
      chunks. The new "expansion" relations get another  relkind,
      so  they  can  be  hidden  from the user and the system can
      easily identify them as such.

    - The type specific functions call a central support function
      to  get the usual VARLENA format, which is taken from a LRU
      cache or fetched from  the  extension  relation.  They  are
      responsible  for freeing the memory after they're done with
      the value. Some macro's should make  it  fairly  simple  to
      handle.

    I  don't  think  it  is  a  good idea to create the expansion
    relation all the time. Some keyword in CREATE  TABLE,  and/or
    another ALTER TABLE should do it instead, so the DB admin can
    activate the LONG feature on a per table base as  needed.  In
    the   first  implementation  there  will  be  no  command  to
    deactivate it again. Workaround is rename  table  and  select
    into as usual.

    Also  I  would  like to say that system relations cannot have
    expansion relations.  At  least  not  until  we  have  enough
    experience with this stuff.

    Is  that  now  what we initially want to give a try? If so, I
    would like to start soon to get the generic part ready  ASAP.
    Others  could  then  join  in  and  contribute by adding LONG
    support for all the VARLENA data types we have.

    Would really be a big leap if we can get this finished for  a
    reasonable number of VARLENA types by February 1.


Jan

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