[Monetdb-developers] Re: [MonetDB-users] speed comparison off inserts and deletes, and db size question
Niels.Nes at cwi.nl
Wed Aug 3 13:12:11 CEST 2005
On Wed, Aug 03, 2005 at 12:42:33PM +0200, Joel Reymont wrote:
> On Aug 3, 2005, at 10:40 AM, Fabian wrote:
> >You should keep in mind that if you use a (V)OID on an 32-bits
> >platform, that you have a limitation of the number of rows that you
> >can contain in a BAT. Also, and OID cannot be bigger than the int
> >it is, so if you do need more rows, or sequence numbers that are
> >higher, you will have to jump over to lng and do the sequence
> >numbers yourself or something.
> Is it 2^32-1 for the maximum number of rows in a BAT?
its even 2^31-1 as internally monet only knows signed values.
As MonetDB is a main memory db it requires all (needed) bats to
be in memory (we basicaly assume there is enough virtual memory).
But on a 32 bit system this will give problems, ie you'll run out of
address space. A 32 bits system can only address 4GB. This means
your database workset (those bats currently in use) cannot exceed
> >You can never join BATs that are bigger than max(OID), so you have
> >to play tricks like doing the selects on all it's subparts and then
> >unioning the results, given they are small enough to be stored in
> >one BAT.
> Are you referring to BAT * BATkunion (BAT *b, BAT *c) in the kernel
indeed BAT(k/s)union are the gdk functions which implement the union
operator on bats.
> I assume that I need to use BATkunion as opposed to BATsunion since
> I'm looking only at the head column. And that the fragments satisfy
> the set property since they are fragments of a larger BAT with a non-
> repeating oid range. Am I thinking right?
Kunion indeed looks only at the head for its double elemination (ie for the
set properties). Having two void headed bats this could be done relatively
cheap as the non disjoint ranges could be easily found.
> Do I need to set any properties on the BAT for the union to work?
> Thanks, Joel
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Niels Nes, Centre for Mathematics and Computer Science (CWI)
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