Re: Parsing of VIEW definitions

On Saturday, February 8, 2003, at 11:54  AM, Tom Lane wrote:
> "Eric B.Ridge" <ebr@tcdi.com> writes:
>> I'm just curious...
>> If you have a view:

<snip>

>> What, behind the scenes, actually happens?
>
> There's a pretty good description in the Programmer's Guide:
> http://www.ca.postgresql.org/users-lounge/docs/7.3/postgres/rules.html
>
> After reading that you can try looking at it for yourself.  For
> example:

Tom, thanks for explaining this.  Your explanation and the docs really
cleared things up.  But I still have a few questions...

<snip>

>> Is the definition of "foo_view" looked up in the system catalog, query
>> rewritten, parsed, then executed?
>
> The Query representation is rebuilt from this textual form and then
> substituted into the referencing query.  I wouldn't call that
> "parsing",

So the text form of the Query *is* looked up in pg_rewrite on every
use?  Or is it looked up only once (per backend maybe?)?  The docs
didn't say... unless I overlooked it.

> though --- the work of the parser phase is long over.  See
> http://www.ca.postgresql.org/users-lounge/docs/7.3/postgres/
> overview.html

<snip>

> What the planner sees is practically indistinguishable from what it
> sees if you
> write out the view's definition as a sub-select like that.  Exercise
> for

So what should be more efficient?  Re-parsing/planning the entire SQL
string (w/ the "view" definition in-line) or actually using the view?
How much overhead is really involved in getting the "textual form" and
turning it into a Query?

I guess my real question is (from a pure performance standpoint):  If
I'm trying to trim every last millisecond off query execution time,
should I be using views?

thanks!

eric