From: Andrei Bintintan <klodoma@ar-sd.net>
To: Ragnar Hafstað <gnari@simnet.is>
To: pgsql-performance@postgresql.org
Cc: pgsql-sql@postgresql.org
Subject: Re: [SQL] OFFSET impact on Performance???
Date: Fri, 21 Jan 2005 11:20:48 +0200
Message-ID: <00c001c4ff9a$809918e0$0b00a8c0@forge> (raw)
References: <019f01c4fee1$1b58d600$0b00a8c0@forge>
<41EF9FD3.5020400@archonet.com>
<020d01c4fef6$595bb9d0$0b00a8c0@forge>
<87pt00c9zd.fsf@stark.xeocode.com>
<1106248326.22416.22.camel@localhost.localdomain>
<1106248992.22416.25.camel@localhost.localdomain>
Now I read all the posts and I have some answers.
Yes, I have a web aplication.
I HAVE to know exactly how many pages I have and I have to allow the user to
jump to a specific page(this is where I used limit and offset). We have this
feature and I cannot take it out.
>> > SELECT * FROM tab WHERE col > ? ORDER BY col LIMIT 50
Now this solution looks very fast, but I cannot implement it, because I
cannot jump from page 1 to page xxxx only to page 2. Because I know with
this type where did the page 1 ended. And we have some really complicated
where's and about 10 tables are involved in the sql query.
About the CURSOR I have to read more about them because this is my first
time when I hear about.
I don't know if temporary tables are a solution, really I don't think so,
there are a lot of users that are working in the same time at the same page.
So... still DIGGING for solutions.
Andy.
----- Original Message -----
From: "Ragnar Hafstað" <gnari@simnet.is>
To: <pgsql-performance@postgresql.org>
Cc: "Andrei Bintintan" <klodoma@ar-sd.net>; <pgsql-sql@postgresql.org>
Sent: Thursday, January 20, 2005 9:23 PM
Subject: Re: [PERFORM] [SQL] OFFSET impact on Performance???
> On Thu, 2005-01-20 at 19:12 +0000, Ragnar Hafstað wrote:
>> On Thu, 2005-01-20 at 11:59 -0500, Greg Stark wrote:
>>
>> > The best way to do pages for is not to use offset or cursors but to use
>> > an
>> > index. This only works if you can enumerate all the sort orders the
>> > application might be using and can have an index on each of them.
>> >
>> > To do this the query would look something like:
>> >
>> > SELECT * FROM tab WHERE col > ? ORDER BY col LIMIT 50
>> >
>> > Then you take note of the last value used on a given page and if the
>> > user
>> > selects "next" you pass that as the starting point for the next page.
>>
>> this will only work unchanged if the index is unique. imagine , for
>> example if you have more than 50 rows with the same value of col.
>>
>> one way to fix this is to use ORDER BY col,oid
>
> and a slightly more complex WHERE clause as well, of course
>
> gnari
>
>
>
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To: pgsql-sql@postgresql.org
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Subject: Re: [SQL] OFFSET impact on Performance???
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