Archives of the TeradataForum
Message Posted: Sun, 12 Dec 2004 @ 09:17:56 GMT
| Subj: | | Re: Ferret PackDisk Basic Questions |
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| From: | | Dennis Calkins |
On Sat, 11 Dec 2004 06:04:59 -0500, Anomy Anom wrote:
| | I have few more basic questions regarding ferret | |
| | a. Do ferret releases physical space e.g. Table a is 10 mb after packing it becomes 8 mb ? | |
No it releases the SLACK space between the Datablocks. This space is UNACCOUNTED for in space accounting so a 10 MEG table is still 10 MEG
regardless of how it is packed. It is just that if a 10 MEG table is at 25% FSP, it means there is 2.5 GIG of FREE SPACE inter mingled between the
datablocsk so the table actually occupies 12.5 GIG of disk space.
| | b. What are benifits of Packdisk, is it Performance ? | |
PERFORMANCE is a tricky issue. Packing a TABLE up tight ( 0%fsp) will make READS really fast because there are fewer cylinders to READ.
However if you insert into that table we will have to CYL SPLIT the cylinder to do the INSERT and that will take time.
| | c. what is the FSP percentage needed in theory i.e. Zero is OK, | |
That is why I said in my other post....There are better people than me on this Board who can debate the wonders of FSP on READS and WRITES and
LOAD issues and what the BSET FSP is for what you are doing.
But look at your last post the FSPs listed. The total number of cylinders on AMP 21 was < 700. At about 2 MEG a cylinder, that means this
amp only occupies 1.4 GIG of disk space.
If have 21 AMPS it means you have at least a 4 NODE system and typical configurations would put at least 1 PDISK per AMP and that would be at
least 4 GIG even on our oldest model or 18 or 36 GIG on our newer ones.
Run Ferret SHOWSPACE and look at the FREE column on the FAR RIGHT (you might have to SCROLL over there). That is the FREE SPACE on your
amps.
If it is more than 50% of your disk don't worry about packdisk.
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