Re: Best way to "add" columns

> Martijn van Oosterhout <kleptog@cupid.suninternet.com> writes:
> > Marten Feldtmann wrote:
> >> The varable lengths columns should be at the end of the row, therefore
> >> it does not seem to be good to add an integer column after a varchar
> >> column.
>
> > 1. Is this true? Should variable length column really be at the end
> > of a row?
>
> There is some microscopic performance advantage if you put fixed-width
> columns before variable-width columns: columns that are at a fixed
> offset in the table records don't require scanning through earlier
> columns to access. But I'd be surprised if you could actually measure
> any difference, unless perhaps on tables with hundreds of columns.
>
> > 2. If so, surly postgres can reorder tham internally so that on disk
> > they are in the optimal format.
>
> There are notes in the source code indicating that the original
> Berkeley Postgres crew thought about this and decided it wasn't
> worth the trouble.

Yes, agreed.  Can anyone measure the difference.  It would show up
accessing columns past the variable length column.

--
  Bruce Momjian                        |  http://www.op.net/~candle
  pgman@candle.pha.pa.us               |  (610) 853-3000
  +  If your life is a hard drive,     |  830 Blythe Avenue
  +  Christ can be your backup.        |  Drexel Hill, Pennsylvania 19026