On Tue, Dec 15, 2009 at 04:29:26PM -0800, Jeff Davis wrote:
> On Tue, 2009-12-15 at 18:06 -0600, decibel wrote:
> > Now that varlena's don't have an enormous fixed overhead, perhaps it's
> > worth looking at using them. Obviously some operations would be
> > slower, but for your stated examples of auditing and history, I
> > suspect that you're not going to notice the overhead that much.
>
> For most varvarlena types, you only get stuck with the full alignment
> burden if you get unlucky. In this case, we're moving from 16 bytes to
> 17, which really means 24 bytes with alignment. Try creating two tables:
>
> create table foo(i int8, t1 timestamp, t2 timestamp);
> create table bar(i int8, c "char", t1 timestamp, t2 timestamp);
But a period type will take just one or two more bytes if you don't
require alignment. Alignment on a varlena type seems silly anyway,
since you'll be aligning the header byte rather than the content.
In the implementation you may need to copy the content before
processing to satisfy the alignment of the contained type, but that's
just a SMOP.
Have a nice day,
--
Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/
> Please line up in a tree and maintain the heap invariant while
> boarding. Thank you for flying nlogn airlines.