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

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