Обсуждение: tuning

hi-

i would like to see if someone could recommend something
to make my query run faster.

System specs:
PostgreSQL 7.4.2 on RedHat 9
dual AMD Athlon 2GHz processors
1 gig memory
mirrored 7200 RPM IDE disks

Values in postgresql.conf:
shared_buffers = 1000
sort_mem is commented out
effective_cache_size is commented out
random_page_cost is commented out

Relevant tables:
product
-------
  id serial
  productlistid integer
  vendorid integer
  item varchar(32)
  descrip varchar(256)
  price double

vendor
------
  id serial
  vendorname varchar(64)

A view i made in order to easily retrieve the vendor name:
create view productvendorview as select p.id, p.productlistid,
v.vendorname, p.item, p.descrip, p.price from product p, vendor v where
p.vendorid = v.id;

Here are some indices i have created:
create index product_plid on product (productlistid);
create index product_plidloweritem on product (productlistid, lower(item) varchar_pattern_ops);
create index product_plidlowerdescrip on product (productlistid, lower(descrip) varchar_pattern_ops);

Here is the query in question:
select * from productvendorview where (productlistid=3 or productlistid=5
or productlistid=4) and (lower(item) like '9229%' or lower(descrip) like
'toner%') order by vendorname,item limit 100;

This query scans 412,457 records.

Here is the EXPLAIN ANALYZE for the query:

  Limit  (cost=45718.83..45719.08 rows=100 width=108) (actual time=39093.636..39093.708 rows=100 loops=1)
    ->  Sort  (cost=45718.83..45727.48 rows=3458 width=108) (actual time=39093.629..39093.655 rows=100 loops=1)
          Sort Key: v.vendorname, p.item
          ->  Hash Join  (cost=22.50..45515.57 rows=3458 width=108) (actual time=95.490..39062.927 rows=2440 loops=1)
                Hash Cond: ("outer".vendorid = "inner".id)
                ->  Seq Scan on test p  (cost=0.00..45432.57 rows=3457 width=62) (actual time=89.066..39041.654
rows=2444loops=1) 
                      Filter: (((productlistid = 3) OR (productlistid = 5) OR (productlistid = 4)) AND
                               ((lower((item)::text) ~~ '9229%'::text) OR (lower((descrip)::text) ~~ 'toner%'::text)))
                ->  Hash  (cost=20.00..20.00 rows=1000 width=54) (actual time=6.289..6.289 rows=0 loops=1)
                      ->  Seq Scan on vendor v  (cost=0.00..20.00 rows=1000 width=54) (actual time=0.060..3.653
rows=2797loops=1) 
  Total runtime: 39094.713 ms
(10 rows)


Thanks!
-Clark

list wrote:
> hi-
>
> i would like to see if someone could recommend something
> to make my query run faster.
>
>
> Values in postgresql.conf:
> shared_buffers = 1000
> sort_mem is commented out
> effective_cache_size is commented out
> random_page_cost is commented out
>

I would increase shared_buffers (say 5000 - 10000), and also
effective_cache_size (say around 20000 - 50000 - but work out how much
memory this box has free or cached and adjust accordingly).

 From your explain output, it looks like sorting is not too much of a
problem - so you can leave it unchanged (for this query anyway).

> Here is the query in question:
> select * from productvendorview where (productlistid=3 or
> productlistid=5 or productlistid=4) and (lower(item) like '9229%' or
> lower(descrip) like 'toner%') order by vendorname,item limit 100;
>

You might want to break this into 2 queries and union them, so you can
(potentially) use the indexes on productlistid,lower(item) and
productlistid, lower(descrip) separately.


> This query scans 412,457 records.
>
> Here is the EXPLAIN ANALYZE for the query:
>
>  Limit  (cost=45718.83..45719.08 rows=100 width=108) (actual
> time=39093.636..39093.708 rows=100 loops=1)
>    ->  Sort  (cost=45718.83..45727.48 rows=3458 width=108) (actual
> time=39093.629..39093.655 rows=100 loops=1)
>          Sort Key: v.vendorname, p.item
>          ->  Hash Join  (cost=22.50..45515.57 rows=3458 width=108)
> (actual time=95.490..39062.927 rows=2440 loops=1)
>                Hash Cond: ("outer".vendorid = "inner".id)
>                ->  Seq Scan on test p  (cost=0.00..45432.57 rows=3457
> width=62) (actual time=89.066..39041.654 rows=2444 loops=1)
>                      Filter: (((productlistid = 3) OR (productlistid =
> 5) OR (productlistid = 4)) AND
>                               ((lower((item)::text) ~~ '9229%'::text) OR
> (lower((descrip)::text) ~~ 'toner%'::text)))
>                ->  Hash  (cost=20.00..20.00 rows=1000 width=54) (actual
> time=6.289..6.289 rows=0 loops=1)
>                      ->  Seq Scan on vendor v  (cost=0.00..20.00
> rows=1000 width=54) (actual time=0.060..3.653 rows=2797 loops=1)
>  Total runtime: 39094.713 ms
> (10 rows)
>

I guess the relation 'test' is a copy of product (?)

Cheers

Mark