Re: Index/Foreign Key Question

On Fri, 2003-10-10 at 16:32, David Busby wrote:
> ----- Original Message -----
> From: "Ron Johnson"
> > On Fri, 2003-10-10 at 16:04, David Busby wrote:
> > > List,
> > > I'm creating this multi company POS database.
> > > My inventory table looks like (all items are unique):
> > >
> > > id,category_id,invoice_id,x,y,z,gid,uid
> > >
> > > I have a primary key on id, and then an foreign keys on category_id and
> > > invoice_id.
> > > GID is the group ID of the company, UID is the companies user, they are
> also
> > > connected via foreign key to the respective tables. My question is
> this: Do
> > > I need to create more indexes on this table when inventory selects look
> like
> > >
> > > select * from inventory where
> > > category_id = 1 and invoice_id is null and gid = 2
> > >
> > > So where would the indexes need to be placed? Or since I have the FK
> setup
> > > are the indexes already in place? I expect to soon have >500K items in
> the
> > > inventory table and don't want it to slow down. I'll have the same type
> of
> > > issue with clients, invoices, purchase_orders and perhaps more
> >
> > I'd make a multi-segment (non-unique?) index on:
> > GID
> > CATEGORY_ID
> > INVOICE_ID
> >
>
> So the multi column index would be better than the three individual indexes?

Yes, because it more closely matches the WHERE clause. Otherwise,
it would have to look thru all three indexes, comparing OIDs.

> Does PostgreSQL only pick one index per table on the select statements?

That's it's preference.

> What about the option of using schemas to segment the data? That would
> eliminate the GID column and help performance correct? It also means I have
> to make company_a.invoice and company_b.invoice tables huh?

Yes, any time you add or alter a table, you'd have to do it on all
the schemas. However, multiple schemas would protect each company's
data from the other, and if the table structures are stable the
maintenance costs are low.

Also, you could script the mods, to reduce the work even more.

Also, you could have multiple databases. This isn't Oracle, so
have as many as you want. The benefit of this method is scalability.
I.e., if the load grows too high, just buy another box, and move
1/2 the databases to it.

--
-----------------------------------------------------------------
Ron Johnson, Jr. ron(dot)l(dot)johnson(at)cox(dot)net
Jefferson, LA USA

"Our computers and their computers are the same color. The
conversion should be no problem!"
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