Re: query planner and scanning methods

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;

--
Regards,
Richard Broersma Jr.

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