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From:Willie Gnarlson Date:April 20 2005 9:46pm
Subject:Re: Unique items from all columns, very slow
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On 4/20/05, SGreen@stripped <SGreen@stripped> wrote:
> Willie Gnarlson <willie.gnarlson@stripped> wrote on 04/20/2005 01:56:03 PM:
>  > On 4/20/05, Dan Nelson <dnelson@stripped> wrote:
>  > > In the last episode (Apr 20), Willie Gnarlson said:
>  > > > I have been attempting to uncover a fast method for retrieving
> unique
>  > > > items from every column in a table. The table has approximately 60
>  > > > thousand rows. Each row has an index associated with it, and running
>  > > > 'explain select distinct class from dlist' shows that it is using
> the
>  > > > index.
>  > > >
>  > > > However, since there are 24 columns, running that select query for
>  > > > each column takes about 4 long seconds on a P4 2.4 Ghz.
>  > > 
>  > > If there are a significant number of identical values (ages, sizes,
>  > > etc), then setting PACK_KEYS=1 on the table may help by making smaller
>  > 
>  > There are, but PACK_KEYS=1 seemed to shed about a second (just
>  > guessing, but it did seem only slightly faster) off the total query
>  > time.
>  > 
>  > > indexes.  You might also be able to convert some columns to ENUMs,
>  > > which will make their indexes even smaller (and let your SELECT be
>  > > almost instantaneous if mysql knows how to optimize it right :)
>  > 
>  > One column was already ENUM, but it wouldn't be possible to make any
>  > others that type.
>  >  
>  > > Another alternative would be to build a table for each column, holding
>  > > the output of SELECT DISTINCT(column) FROM dlist.  Rebuild it as
>  > > frequently as needed.
>  > 
>  > Okay, I decided to try that option, as it sounded like a good one. I
>  > created the tables, and since the main table would be rarely updated I
>  > was going to run DELETE FROM on the column tables and run the queries
>  > `INSERT INTO table (col) SELECT DISTINCT col FROM dlist' each time a
>  > new record was updated or added.
>  > 
>  > It turns out that is almost as slow as the original method. So then I
>  > added an index to every column table, and it was still no better.
>  > 
>  > I thought maybe generating a select box for each column's contents was
>  > the problem, since unique items in some tables are as much as 4
>  > thousand, but singling out the code which performs the queries,
>  > eliminating the select box generation, confirmed that the queries were
>  > indeed the slow part.
>  > 
>  > I may have to abandon the retrieving of unique items from every column
>  > in a table unless you or anyone else have any other ideas.

(...)

> If you are using select boxes for every column, how can you possibly worry
> about new or changed values as the users must pick from a fixed list of
> values, don't they? 

I am building (or attempting tobuild) the select boxes on the fly
based on unique items from columns in the table.
  
> You don't rebuild _all_ of your umpteen pick-list tables from scratch every
> time, detect just the new or changed values and add/update them (which goes

Yes, that would be the smarter thing to do, you're right. But alas
that can be set aside for my testing so far. At this point I'm simply
trying to get the values from the columns in a reasonable amount of
time.

> back to my original question of how are the users creating new values if you
> are really using a select box and not something else like a combo box (part
> list, part text field)) 

Okay, they aren't creating new values using that form. The form I've
been talking about is a form to limit results from the database to
only specific values for  specific fields without the user having to
know from memory what the possible values are (plus, they'll change
every so often).
  
> Maybe if I understood your front-end application a little bit better, I
> could help you work around the issue. The way you described your user
> interface design made me wince; something just doesn't feel right about it. 

No, it's not as bad as it sounds. :-) (I hope)

-- 
Willie Gnarlson
Thread
Unique items from all columns, very slowWillie Gnarlson20 Apr
  • Re: Unique items from all columns, very slowDan Nelson20 Apr
    • Re: Unique items from all columns, very slowWillie Gnarlson20 Apr
      • Re: Unique items from all columns, very slowSGreen20 Apr
        • Re: Unique items from all columns, very slowWillie Gnarlson20 Apr
          • Re: Unique items from all columns, very slowSGreen21 Apr
            • Re: Unique items from all columns, very slowWillie Gnarlson21 Apr
              • Re: Unique items from all columns, very slowWillie Gnarlson21 Apr
              • Re: Unique items from all columns, very slowSGreen21 Apr
                • Re: Unique items from all columns, very slowWillie Gnarlson21 Apr