Thread

1. TOAST & vacuum

   Jan Wieck <janwieck@t-online.de> — 2000-07-21T10:30:36Z

   FYI,
   
       TOAST  is now vacuum-safe. When needed, the toaster creates a
       second  heap  tuple,  containing  only  plain  or  compressed
       values.  This one is then returned by the heap access methods
       to  the  caller,  so  indices  will  never  contain  external
       references.
   
       The  changes  are  covered  by  #ifdef  TOAST_INDICES, so can
       easily be disabled at the time we have  file  versioning  and
       can recreate indices during vacuum.
   
   
   Jan
   
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2. Re: TOAST & vacuum

   Tom Lane <tgl@sss.pgh.pa.us> — 2000-07-21T18:29:50Z

   JanWieck@t-online.de (Jan Wieck) writes:
   >     TOAST  is now vacuum-safe. When needed, the toaster creates a
   >     second  heap  tuple,  containing  only  plain  or  compressed
   >     values.  This one is then returned by the heap access methods
   >     to  the  caller,  so  indices  will  never  contain  external
   >     references.
   
   That should be sufficient for insertions into existing indexes,
   but what about CREATE INDEX on a column that already contains
   toasted values?  That works with fetched tuples, not ones formed
   during insert/update.
   
   I think a cleaner and more reliable short-term hack would be to twiddle
   index_formtuple() to detoast any externally-stored attributes.  AFAIK,
   in current sources all paths for creating an index tuple go through that
   routine, and it has a tupdesc handy so it knows which attributes are of
   varlena type.
   
   This way you wouldn't need to hack up the tuptoaster itself.
   
   Also, this would work for functional indexes whereas the way you are
   doing it will not (a function could return a toasted Datum extracted
   from some other table, no?).
   
   			regards, tom lane
   
   

3. Re: TOAST & vacuum

   Jan Wieck <janwieck@t-online.de> — 2000-07-22T09:28:25Z

   Tom Lane wrote:
   > JanWieck@t-online.de (Jan Wieck) writes:
   > >     TOAST  is now vacuum-safe. When needed, the toaster creates a
   > >     second  heap  tuple,  containing  only  plain  or  compressed
   > >     values.  This one is then returned by the heap access methods
   > >     to  the  caller,  so  indices  will  never  contain  external
   > >     references.
   >
   > That should be sufficient for insertions into existing indexes,
   > but what about CREATE INDEX on a column that already contains
   > toasted values?  That works with fetched tuples, not ones formed
   > during insert/update.
   >
   > I think a cleaner and more reliable short-term hack would be to twiddle
   > index_formtuple() to detoast any externally-stored attributes.  AFAIK,
   > in current sources all paths for creating an index tuple go through that
   > routine, and it has a tupdesc handy so it knows which attributes are of
   > varlena type.
   >
   > This way you wouldn't need to hack up the tuptoaster itself.
   
       You're right. Will do it that way.
   
   > Also, this would work for functional indexes whereas the way you are
   > doing it will not (a function could return a toasted Datum extracted
   > from some other table, no?).
   
       Don't know of a function that does it that way right now. But
       that doesn't mean no such exists  -  you're  right  again.  2
       donut's for U.
   
   
   Jan
   
   --
   
   #======================================================================#
   # It's easier to get forgiveness for being wrong than for being right. #
   # Let's break this rule - forgive me.                                  #
   #================================================== JanWieck@Yahoo.com #
   
   
   
   

4. Re: TOAST & vacuum

   Bruce Momjian <pgman@candle.pha.pa.us> — 2000-07-27T02:10:05Z

   > FYI,
   > 
   >     TOAST  is now vacuum-safe. When needed, the toaster creates a
   >     second  heap  tuple,  containing  only  plain  or  compressed
   >     values.  This one is then returned by the heap access methods
   >     to  the  caller,  so  indices  will  never  contain  external
   >     references.
   > 
   >     The  changes  are  covered  by  #ifdef  TOAST_INDICES, so can
   >     easily be disabled at the time we have  file  versioning  and
   >     can recreate indices during vacuum.
   
   Seems this has some performance advantages.  Un-toasting to traverse a
   btree index would be pretty slow.  This way, it is all in the index.
   
   -- 
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