Re: Column storage positions

Phil Currier wrote:
> On 2/21/07, Alvaro Herrera <alvherre@commandprompt.com> wrote:
> > I'd expect the system being able to reoder the columns to the most
> > efficient order possible (performance-wise and padding-saving-wise),
> > automatically.  When you create a table, sort the columns to the most
> > efficient order; ALTER TABLE ADD COLUMN just puts the new columns at the
> > end of the tuple; and anything that requires a rewrite of the table
> > (ALTER TABLE ... ALTER TYPE for example; would be cool to have CLUSTER
> > do it as well; and do it on TRUNCATE also) again recomputes the most
> > efficient order.
> 
> That's exactly what I'm proposing.  On table creation, the system
> chooses an efficient column order for you.  The next time an ALTER
> TABLE operation forces a rewrite, the system would recompute the
> column storage order.  I hadn't thought of having CLUSTER also redo
> the storage order, but that seems safe since it takes an exclusive
> lock on the table.  I'm less sure about whether it's safe to do this
> during a TRUNCATE.

Keep in mind we have a patch in process to reduce the varlena length and
reduce alignment requirements, so once that is in, reordering columns
will not be as important.

--  Bruce Momjian  <bruce@momjian.us>          http://momjian.us EnterpriseDB
http://www.enterprisedb.com
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