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

--

#======================================================================#
# It's easier to get forgiveness for being wrong than for being right. #
# Let's break this rule - forgive me.                                  #
#================================================== JanWieck@Yahoo.com #



Fri, 21 Jul 2000 12:30:36 +0200 (MEST)
JanWieck@t-online.de (Jan Wieck)
TOAST & vacuum
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

Fri, 21 Jul 2000 14:29:50 -0400
Tom Lane <tgl@sss.pgh.pa.us>
Re: TOAST & vacuum 
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 #



Sat, 22 Jul 2000 11:28:25 +0200 (MEST)
JanWieck@t-online.de (Jan Wieck)
Re: TOAST & vacuum
> 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.

-- 
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 853-3000
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Wed, 26 Jul 2000 22:10:05 -0400 (EDT)
Bruce Momjian <pgman@candle.pha.pa.us>
Re: TOAST & vacuum