RE: rule of thumb or words of wisdom for btree cleaners?

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04-20-2008, 07:51 AM

Alexey Sonkin

Posts: n/a

RE: rule of thumb or words of wisdom for btree cleaners?

Norma,

After a thorough investigation of how the BTSCANNER works,
I can suggest a rule of a thumb:

1. ALWAYS change btscanner from the default 'leaf scan'
to 'range scan' with a range scan threshold equal to
1-5 % of Informix cache, like:

onmode -C rangesize 10000

2. ALWAYS increase the 'number of dirty items' threshold
to something MUCH higher then the default CRAZY value of 500:

onmode -C threshold 50000

This threshold can be temporary changed to even higher value
during massive data deletes

3. If (1) and (2) is set properly, don't care about allocating
additional threads

-Alexey

> -----Original Message-----
> From: owner-informix-list@iiug.org
[mailto

wner-informix-list@iiug.org] On
> Behalf Of NormaJean
> Sent: Friday, March 04, 2005 10:26 AM
> To: informix-list@iiug.org
> Subject: rule of thumb or words of wisdom for btree cleaners?
>
> All,
> Does anyone have a rule of thumb or words of wisdom regarding
additonal
> btree cleaners?
> Looking at the output below it seems I could benefit from adding an
> additional cleaner
>
> Stats reset at 8:30 AM
> HPUX 11
> $ onstat -C
>
> IBM Informix Dynamic Server Version 9.40.FC2W4 -- On-Line -- Up 3
days
> 14:50:17 -- 4460564 Kbytes
>
> Btree Cleaner Info
> BT scanner profile Information
> ==============================
> Active Threads 1
> Global Commands 0
> Number of partition scans 23
> Main Block 0xc0000000e0a97cc8
> BTC Admin 0x0000000000000000
>
>
> BTS info id Prio Partnum Key Cmd
> 0xc0000000e0eb58b0 0 Low 0x055007F4 1 100000 Scan index
> Number of leaves pages scanned 10623920
> Number of leaves with deleted items 122292
> Time spent cleaning (sec) 22243
> Number of index compresses 39214
> Number of deleted items 4660843
> Number of index range scans 0
> Number of index leaf scans 259
> Scan Type Leaf
>
>
>
> Darren Jacobs/Carmax
>

sending to informix-list

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RE: rule of thumb or words of wisdom for btree cleaners?