From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
---|---|
To: | Bruce Momjian <bruce(at)momjian(dot)us> |
Cc: | Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: procost for to_tsvector |
Date: | 2015-05-01 13:39:43 |
Message-ID: | CA+TgmoYLFhmAaisxOTfnA-nw3smLJiqo5o6h+Ava1tZCx7z3MA@mail.gmail.com |
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Lists: | pgsql-hackers |
On Fri, May 1, 2015 at 9:13 AM, Bruce Momjian <bruce(at)momjian(dot)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(at)momjian(dot)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
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company
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