Re: procost for to_tsvector

On Fri, May 1, 2015 at 9:13 AM, Bruce Momjian <bruce@momjian.us> wrote:
> On Fri, May  1, 2015 at 07:57:27AM -0400, Robert Haas wrote:
>> On Thu, Apr 30, 2015 at 9:34 PM, Bruce Momjian <bruce@momjian.us> wrote:
>> > On Wed, Mar 11, 2015 at 02:40:16PM +0000, Andrew Gierth wrote:
>> >> An issue that comes up regularly on IRC is that text search queries,
>> >> especially on relatively modest size tables or for relatively
>> >> non-selective words, often misplan as a seqscan based on the fact that
>> >> to_tsvector has procost=1.
>> >>
>> >> Clearly this cost number is ludicrous.
>> >>
>> >> Getting the right cost estimate would obviously mean taking the cost of
>> >> detoasting into account, but even without doing that, there's a strong
>> >> argument that it should be increased to at least the order of 100.
>> >> (With the default cpu_operator_cost that would make each to_tsvector
>> >> call cost 0.25.)
>> >>
>> >> (The guy I was just helping on IRC was seeing a slowdown of 100x from a
>> >> seqscan in a query that selected about 50 rows from about 500.)
>> >
>> > Where are we on setting increasing procost for to_tsvector?
>>
>> We're waiting for you to commit the patch.
>
> OK, I have to write the patch first, so patch attached, using the cost
> of 10.  I assume to_tsvector() is the ony one needing changes.  The
> patch will require a catalog bump too.

Andrew did the research to support a higher value, but even 10 should
be an improvement over what we have now.

-- 
Robert Haas
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