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IDS Forum

Re: Question about sysindexes.clust

Posted By: Obnoxio The Clown
Date: Tuesday, 18 November 2008, at 3:01 p.m.

In Response To: Re: Question about sysindexes.clust (Eric Rowell)

Eric Rowell wrote:
> The following is the explain plain for the only query in the program which
> isn't running correctly. The first is the plan from the normal run (filter
> data had to be changed to project my job). The info after that is from a
> diff of the explain outs for 2 more configurations. Also during all tests
> we used a production like system (smaller CPU and slower SAN) but we know
> the approx. modifier from prod to dev. When we sorted the data by the
> serial_link and reloaded (changing the fragmentation as shown earlier things
> run much better.
>
> EXPLAIN from normal run...
>
> QUERY:
> ------
> SELECT qd.option_list, oq.optid
> FROM qty_head qh, qty_det qd, optcombo_qty oq
> WHERE ((qh.set_no = "FINDA" AND qh.version = "09") OR
>
> (qh.set_no = "ORFND" AND qh.version = "01"))
>
> AND qh.serial_key = qd.serial_link
>
> AND qd.serial_key = oq.option_group_id
>
> AND qh.dept_code IN ("AAA","BBB","CCC","DDD","EEE")
>
> AND qh.community = "00"
>
> Estimated Cost: 1049986
> Estimated # of Rows Returned: 1083718
> 1) informix.qh: INDEX PATH
>
> (1) Index Keys: dept_code community set_no version phase_no lot
> area_group_id
>
> (Key-First) (Serial, fragments: ALL)
>
> Lower Index Filter: (informix.qh.dept_code = 'AAA' AND
> informix.qh.community = '00' )
>
> Index Key Filters: (( (informix.qh.set_no = 'FINDA' AND
> informix.qh.version = '09')
>
> OR (informix.qh.set_no = 'ORFND' AND
> informix.qh.version = '01')))
>
> (2) Index Keys: dept_code community set_no version phase_no lot
> area_group_id
>
> (Key-First) (Serial, fragments: ALL)
>
> Lower Index Filter: (informix.qh.dept_code = 'BBB' AND
> informix.qh.community = '00' )
>
> Index Key Filters: (( (informix.qh.set_no = 'FINDA' AND
> informix.qh.version = '09')
>
> OR (informix.qh.set_no = 'ORFND' AND
> informix.qh.version = '01')))
>
> (3) Index Keys: dept_code community set_no version phase_no lot
> area_group_id
>
> (Key-First) (Serial, fragments: ALL)
>
> Lower Index Filter: (informix.qh.dept_code = 'CCC' AND
> informix.qh.community = '00' )
>
> Index Key Filters: (( (informix.qh.set_no = 'FINDA' AND
> informix.qh.version = '09')
>
> OR (informix.qh.set_no = 'ORFND' AND
> informix.qh.version = '01')))
>
> (4) Index Keys: dept_code community set_no version phase_no lot
> area_group_id
>
> (Key-First) (Serial, fragments: ALL)
>
> Lower Index Filter: (informix.qh.dept_code = 'DDD' AND
> informix.qh.community = '00' )
>
> Index Key Filters: (( (informix.qh.set_no = 'FINDA' AND
> informix.qh.version = '09')
>
> OR (informix.qh.set_no = 'ORFND' AND
> informix.qh.version = '01')))
>
> (5) Index Keys: dept_code community set_no version phase_no lot
> area_group_id
>
> (Key-First) (Serial, fragments: ALL)
>
> Lower Index Filter: (informix.qh.dept_code = 'EEE' AND
> informix.qh.community = '00' )
>
> Index Key Filters: (( (informix.qh.set_no = 'FINDA' AND
> informix.qh.version = '09' )
>
> OR (informix.qh.set_no = 'ORFND' AND
> informix.qh.version = '01')))
> 2) informix.qd: INDEX PATH
>
> (1) Index Keys: serial_link (Serial, fragments: ALL)
>
> Lower Index Filter: informix.qh.serial_key = informix.qd.serial_link
> NESTED LOOP JOIN
> 3) informix.optcombo_head: INDEX PATH
>
> (1) Index Keys: serial_key option_list option_count (Serial,
> fragments: ALL)
>
> Lower Index Filter: informix.qd.optcombo_head_key =
> informix.optcombo_head.serial_key
> NESTED LOOP JOIN
> 4) product.qty_detail: INDEX PATH
>
> (1) Index Keys: serial_key (Serial, fragments: ALL)
>
> Lower Index Filter: informix.qd.serial_key =
> product.qty_detail.serial_key
> NESTED LOOP JOIN
> 5) informix.oq: INDEX PATH
>
> (1) Index Keys: optcombo_head_key opt_id (Key-Only) (Serial,
> fragments: ALL)
>
> Lower Index Filter: informix.oq.optcombo_head_key =
> product.qty_detail.optcombo_head_key
> NESTED LOOP JOIN
>
> Diff of Explain Plan after just reloading the table:
> < Estimated Cost: 1049986
> < Estimated # of Rows Returned: 1083718
> ---
>> Estimated Cost: 2348476
>> Estimated # of Rows Returned: 1486409
>
> Diff of Explain Plan after reloading the sorting data (using serial_link):
> < Estimated Cost: 1049986
> < Estimated # of Rows Returned: 1083718
> ---
>> Estimated Cost: 851019
>> Estimated # of Rows Returned: 1094319
>
> The cost difference appears to be in line with the change to the
> sysindex.clust value for the indexes.

And which table do you query from to see if there are missing rows and
insert them?

Basically, I can't disagree with your analysis, I'm just curious as to
why ordering should have such a measurable impact on performance given
the explain plan. In general, it doesn't.

I feel like there is something lurking in the nether hells of my brain,
but I can't quite drag it out. Last time I saw something like this, the
root cause was "XXXX in my opinion" but I can't remember what "XXXX" was.

Give me time. Or Art will be along shortly. :o)

--
Cheers,
Obnoxio The Clown

http://obotheclown.blogspot.com

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