Re: query planner and scanning methods

On Sep 23, 2008, at 6:07 PM, Richard Broersma wrote:

> On Tue, Sep 23, 2008 at 2:22 PM, Colin Copeland <copelco(at)caktusgroup(dot)com
> > wrote:
>> dimension=# EXPLAIN ANALYZE
>> SELECT DISTINCT ON ("dimension_book"."call")
>> "dimension_book"."title"
>> FROM "dimension_book"
>> INNER JOIN "dimension_library_books"
>> ON ("dimension_book"."id" =
>> "dimension_library_books"."book_id")
>> WHERE ("dimension_book"."call" >= 'PA0000'
>> AND "dimension_library_books"."library_id" IN (12,15,20))
>> ORDER BY "dimension_book"."call" ASC
>> LIMIT 10 OFFSET 100;
>
> Ya offset works by scanning over the first 100 rows. When the offsets
> get big, it become a performance looser.
>
> You can guarantee a faster index scan if you recall the last 10th
> value from the previous query. Then remove the offset predicate and
> replace it with the following WHERE clause:
>
> WHERE ...
> AND dimension_book.call > _last_queried_10th_row-dimension_book_call,
> ...
> LIMIT 10;

Richard,

Yes, I was thinking about this too. How would one generate a list of
pages from this, though? I can't predict values of dimension_book.call
(it's not a serial number).

Thanks,
colin

--
Colin Copeland
Caktus Consulting Group, LLC
P.O. Box 1454
Carrboro, NC 27510
(919) 951-0052
http://www.caktusgroup.com