Re: Limit clause not using index

These are my indexes

create index ixprintjobsapplicationtype on tblPrintjobs
(applicationtype);
create index ixprintjobsdesceventdate on tblPrintjobs (desceventdate);
create index ixprintjobsdesceventtime on tblPrintjobs (desceventtime);
create index ixprintjobsdescpages on tblPrintjobs (descpages);
create index ixprintjobsdocumentname on tblPrintjobs (documentname) ;
create index ixprintjobseventcomputer on tblPrintjobs (eventcomputer);
create index ixprintjobseventdate on tblPrintjobs (eventdate);
create index ixprintjobseventtime on tblPrintjobs (eventtime);
create index ixprintjobseventuser on tblPrintjobs (eventuser);
create index ixprintjobshostname on tblPrintjobs (hostname) ;
create index ixprintjobsipaddress on tblPrintjobs (ipaddress) ;
create index ixprintjobsloginuser on tblPrintjobs (loginuser) ;
create index ixprintjobspages on tblPrintjobs (pages) ;
create index ixprintjobsprintport on tblPrintjobs (printport) ;
create index ixprintjobsprintqueue on tblPrintjobs (printqueue) ;
create index ixprintjobsrecordnumber on tblPrintjobs (recordnumber) ;
create index ixprintjobssize on tblPrintjobs (size) ;
create index ixprintjobsusertype on tblPrintjobs (usertype) ;
create index ixPrintjobsDescpagesDocumentname on tblPrintjobs
(descpages, documentname) ;
create index ixPrintjobsHostnamePrintqueueDesceventdateDesceventtime
on tblPrintjobs (hostname, printqueue, desceventdate, desceventtime) ;
create index ixPrintjobsLoginDescEventdateDesceventtime on
tblPrintjobs (loginuser, desceventdate, desceventtime) ;

On 21 Jun 2005, at 16:42, Tom Lane wrote:

> Yves Vindevogel <yves(dot)vindevogel(at)implements(dot)be> writes:
>> Can anyone explain me this ?
>
>> rvponp=# explain select * from tblprintjobs order by loginuser,
>> desceventdate, desceventtime offset 25 limit 25 ;
>> QUERY PLAN
>> ----------------------------------------------------------------------
>> --
>> -----------
>> Limit (cost=349860.62..349860.68 rows=25 width=206)
>> -> Sort (cost=349860.56..351416.15 rows=622236 width=206)
>> Sort Key: loginuser, desceventdate, desceventtime
>> -> Seq Scan on tblprintjobs (cost=0.00..25589.36
>> rows=622236 width=206)
>> (4 rows)
>
>
> Do you have an index matching that sort key? I'd certainly expect the
> above to use it if it were there. For the full table case it's not so
> clear --- an indexscan isn't always better.
>
> regards, tom lane
>
>
Met vriendelijke groeten,
Bien à vous,
Kind regards,

Yves Vindevogel
Implements