Re: ALTER TABLE performance issues

[Alan Campin <alan0307d@xxxxxxxxx>]

Could be locks. If they are soft locks, it may take some time to end them.

Could be system load too.

On Mon, Nov 15, 2010 at 3:44 PM, Kruse, Kat <kkruse@xxxxxxxxxxxx> wrote:

> Our developers have finally started using ALTER TABLE instead of
> rename/copy method of changing files.  One of the things we noticed is that
> there are times that there are significant differences in the performance of
> the change.
>
> We've already suggested to them that instead of multiple passes with only
> one change at a time, they should be doing all the changes in a single pass.
>   We've also noted where the differences can be accounted for by files with
> many/few columns and by files with many/few rows.
>
> After taking the above into consideration we're still finding that the
> ALTER TABLE give very inconsistent results.  For example, for a given file
> which had 0 records, in library A it took 5 seconds to finish while in
> library B (also 0 records) it to 22 seconds to finish.
>
> FWIW, we're at V6R1 on Power7.
>
> So, has anyone got suggestions at what we can look at or do to improve our
> performance?
>
> Thanks,
> Kat Kruse
> Qualcomm, Inc.
> Systems Support Engineer
>
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