Re: insertion becoming slow

On Tue, Sep 27, 2005 at 10:24:02AM +0200, Csaba Nagy wrote:
> Hi all,
>
> I've recently asked a similar question, which received no useful answer
> yet, so I'll drop in too.
>
> In my case, the table I was inserting to was a quite big one already to
> start with (and analyzed so), so I was expecting that it will not slow
> down due to indexes, as they were quite big to start with as I said.
>
> What I mean is that I expected that the speed will be more or less
> constant over the whole inserting. But the result was that after a while
> the average insert speed dropped considerably and suddenly, which I
> can't explain and would like to know what caused it...
> The table was ~100 million live rows and quite often updated, and the
> insert was ~40 million rows. After ~10 million rows the average speed
> dropped suddenly about 4 times.
>
> My only suspicion would be that the table had a quite big amount of free
> space in it at the beginning due to the fact that it is quite often
> updated, and then the free space was exhausted. So the speed difference
> might come from the difference in using free space versus creating new
> pages ? Or the same thing for the b-tree indexes.
>
> Is there any other reasonable explanation for this ? As I see this kind
> of behavior consistently, speed OK on start of inserting, and then slow
> down, and I would like to know if I can tune my DB to cope with it or
> just accept that it works like this...
>
> Cheers,
> Csaba.

I can't think of any explanation for this off-hand. Can you re-run the
test on a table that doesn't have a bunch of free space in it to see if
that's what the issue was?
--
Jim C. Nasby, Sr. Engineering Consultant jnasby(at)pervasive(dot)com
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461