Re: Perl Binding affects speed?

From: Martin Kjeldsen, Sent: 2011/2/25, 20:59
>
> On 25/02/2011, at 13.25, Marti Raudsepp wrote:
>
> > On Fri, Feb 25, 2011 at 05:02, Sam Wong <sam(at)hellosam(dot)net> wrote:
> >> * But if I do this - using binding:
> >> $dbh->selectall_arrayref("SELECT * from shipment_lookup WHERE
> >> (UPPER(lookup) LIKE ?)", undef, '0GURG5YGVQA9%'); It took 10 seconds
> >> to finish the query, just like it was using full table scan instead!
> >> Even though the 'explain' shows the same query plan.
> >
> > This is a pretty common shortcoming with placeholders. Since planning
> > of parameterized queries is done *before* binding parameters, the
> > planner has no knowledge of what the "?" placeholder actually is. Thus
> > it often gets the selectivity statistics wrong and produces worse
> > plans for your values.
> >
> > AFAIK the only workaround is to not use variable binding in these
> > cases, but escape and insert your variables straight it into the SQL
> > query.
>
> Instead of not using the placeholder syntax you can use:
>
> local $dbh->{pg_server_prepare} = 0;
>
> which disables prepared queries serverside in the current scope and
> therefore doesn't have the late variable binding issue, but allows you to
> avoid SQL injection attacks.
>

Thanks, I will look into that.

Sam