Re: [firebird-support] Optimizer request

'Djordje Radovanovic' [email protected] [firebird-support] Sun, 11 Sep 2016 01:29:43 -0700

This one makes significiant change.

This time instead of 10000 reads of orders and 10000 reads of partners I 
received exactly what I was asking for.


133 reads of parters table
1335 of orders table

Thank you Arno. Please can you explain me part on the right side of FROM? 
Somewhere in my subconsciousness I have in mind that something like this is 
doable but never read good explanation of that kind of virtual table.

Best reagrds,

Djordje Radovanovic

From: mailto:[email protected] 
Sent: Sunday, September 11, 2016 12:11 AM
To: [email protected] 
Subject: Re: [firebird-support] Optimizer request

  

Which Firebird version are you using?


Does this perform for you as expected:

SELECT
  * 
FROM 
  (SELECT partners.partid + 0 AS PartID FROM partners WHERE partners.country = 
'Spain') dt
  JOIN orders ON (orders.partid = dt.partid)



Kind Regards,
Arno Brinkman


From: mailto:[email protected] 
Sent: Saturday, September 10, 2016 10:05 PM
To: [email protected] 
Subject: Re: [firebird-support] Optimizer request




CREATE TABLE PARTNERS (
    PARTID   INTEGER NOT NULL,
    COUNTRY  CHAR(20)
);
ALTER TABLE PARTNERS ADD CONSTRAINT PK_PARTNERS PRIMARY KEY (PARTID);
CREATE INDEX PARTNERS_IDX1 ON PARTNERS (COUNTRY);

CREATE TABLE ORDERS (
    ORDERNUM   INTEGER NOT NULL,
    ORDERDATE  DATE,
    AMOUNT     DECIMAL(18,2),
    PARTID     INTEGER
);

ALTER TABLE ORDERS ADD CONSTRAINT PK_ORDERS PRIMARY KEY (ORDERNUM);
ALTER TABLE ORDERS ADD CONSTRAINT FK_ORDERS_PARTNERS FOREIGN KEY (PARTID) 
REFERENCES PARTNERS (PARTID) ON DELETE NO ACTION ON UPDATE NO ACTION;

This is tables definitions. So, index exist and after all perfomance analyzer 
gives me same result.
Perfomance analyzer was taken from IBExpert. Whatever I do (as others suggest) 
perfomance are the same. I still vote for changes in optimizer. Right side from 
WHERE clause needs to be evaluated before main query and it is simple and much 
better solution same as Oracle optimize query. 

Firebird is very kind to programmer and has easy to understand, efficient P/SQL 
and some improvements will give us significant efficiency.
.
Djordje

From: mailto:[email protected] 
Sent: Friday, September 09, 2016 10:51 PM
To: [email protected] 
Subject: Re: [firebird-support] Optimizer request

  

On Fri, Sep 9, 2016 at 8:30 AM, 'Djordje Radovanovic' [email protected] 
[firebird-support] <[email protected]> wrote:


  I tried query with subquery in where clause and found big issue for this type 
of subquery.

  select * from orders where orders.partid in (select partners.partid from 
partners where partners.country = ‘Spain’)

  Perfomance Analysis returns me this

  partners     687660 non index reads
  orders          28657 index reads

  If you analyze this result you’ll find that there is 687659 unnecessary non 
index reads. If developer of optimizer accept that all queries on the left side 
of where clause has priority (and there is no way to be opposite) than we have 
big improvement in optimization.

Is there an index on partners.country?  What plans are generated for each query?

If I were writing this query, I'd write

select o.* 
     from orders o
            inner join partners p 
     where p.partid = o.opartid
            and p.country = 'Spain';

All that silliness about "select from (select from )" probably doesn't save 
anything in
this case - it does when the inner select is complicated, but not here.  
Firebird won't
carry around unneeded fields from the partners table.

What is the distribution of partners.country?

Good luck,

Ann
  __,_._,_

Re: [firebird-support] Optimizer request

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