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

http://www.informix.co.uk/btscanner.htm

"NormaJean" <normajean.sebastian@tellabs.com> wrote in message
news:S8%Vd.6$Jo6.2119@news.uswest.net...
> 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
>
>

Perhaps I should call this "words of desperation". Sorry for being
negative. But the most striking thing your numbers show is how much i/o
the btree cleaner wastes.

NormaJean wrote:
> 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

This means that most of the btree cleaner i/o is wasted to visit pages
that don't need cleaning. That's the new btree scanner concept's big
weakness. If you add more cleaners it's possible that they produce even
more overhead.

You could increase the cleaning threshold or use range scans or run the
cleaner (or several of them) only at off hours to reduce the amount of
unnecessary i/o.

Warning: If you do mass deletes followed by mass reinserts of large
ranges of keys this strategy can lead to large insert performance
problems. In this case you have no choice and must do everything to
speed btree cleaning up. In this case you have to live with the large
additional i/o load.

Michael

> 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
>
>