Re: Parallel processing advantages

Scott Watson wrote:
>
> I would like to know if there is any advantage to using parallel processing
> in the following situation. Now before you tell me that it would be better
> to stripe the table across disks and the like I realize that, however, I
> wanted to know if there was any advantage without changing the table
> whatsoever.
>
> Situation.
> 1 table 10,000,000 rows.
> Stored in one tablespace with all datafiles on the same disk.
> Access is read only
>
> Is there any performace increase when scanning a table that is on the same
> disk in parallel or is it better to scan it serially.
>
> My thinking would be as follows. If there was only one user accessing the
> table, and the table was the only object stored on the disk in question then
> parallel processing would not be faster. However, assuming that this is not
> the only object on disk and that multiple user may be using the table at any
> given time then wouldn't PQ be better as n slaves would be able to read
> n*mulit block read count bytes on each read. Therefore getting through the
> table quicker all the while services other request from the same disk.
>
> Thanks for your input.
> Scott Watson.

Theoretically, if there is some IO capacity left on the single disk, then parallel slaves may give some marginal benefit, only because you are now get n/m percent of the disk instead of 1/m, where 'n' is the parallelism and 'm' is the number of users going for the disk...

... but then again, once 'm' gets above (say) 1 or 2, the disk is probably going flat out anyway...hmmmm

Cheers
Connor

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Connor McDonald
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"Some days you're the pigeon, some days you're the statue"