Re: [PATCHES] Eliminate more detoast copies for packed varlenas - Mailing list pgsql-hackers

From Tom Lane
Subject Re: [PATCHES] Eliminate more detoast copies for packed varlenas
Date
Msg-id 5986.1192135845@sss.pgh.pa.us
Whole thread Raw
In response to Re: [PATCHES] Eliminate more detoast copies for packed varlenas  (Tom Lane <tgl@sss.pgh.pa.us>)
List pgsql-hackers
I wrote:
> In fact, it seems there's a different risk here: if such a datum were
> toasted out-of-line, the reference in a cached plan might live longer
> than the underlying toast-table data.  Maybe we need a forcible detoast
> in evaluate_function().

Sure enough, it seems we do.  The attached script fails in every release
back to 7.3.  It's a rather contrived case, because a function marked
immutable probably shouldn't be reading from a table at all, especially
not one you are likely to change or drop.  That's probably why we've not
heard reports of this before.  But it's definitely a bug.
        regards, tom lane

create table big(f1 text);
insert into big values(repeat('xyzzy',100000));

create or replace function getbig() returns text as
'select f1 from big' language sql immutable;

create or replace function usebig(text) returns bool as '
begin return $1 ~ ''xyzzy''; end
' language plpgsql;

prepare foo as select usebig(getbig()) from int4_tbl;

execute foo;

drop table big;

execute foo;


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