Thread: Accessing pg_timezone_names system view

I was wondering if there is any reason that accessing the system view
pg_timezone_names is extremely slow relative to other queries. The
following query:

    SELECT * FROM pg_timezone_names;

Executes in between 29ms and 32ms on my server. It takes about the same
when I put a

    WHERE name = 'some/timezone'

clause in it. To put this into perspective, on the pages that execute
this, it accounts for something like 3/4 of my DB execution time.

Here's a screenshot to show you what I'm talking about:

    http://www.mrnaz.com/dbetime.gif

As you can see, the execution of that single fetch dwarfs all other
processing loads. I've run this a few times, and the timings are always
roughly the same. Is there a way for me to speed this up? Would I be
better off loading these into a static table and executing from there?
It seems kinda purpose defeating to do that though. Perhaps this has
been addressed in 8.3 ? I eagerly await.

Regards,
- Naz

On Fri, Aug 17, 2007 at 11:51:52PM +1000, Naz Gassiep wrote:
> I was wondering if there is any reason that accessing the system view
> pg_timezone_names is extremely slow relative to other queries. The
> following query:
>
>    SELECT * FROM pg_timezone_names;
>
> Executes in between 29ms and 32ms on my server. It takes about the same
> when I put a
>
>    WHERE name = 'some/timezone'
>
> clause in it. To put this into perspective, on the pages that execute
> this, it accounts for something like 3/4 of my DB execution time.

This view is backed by a set returning function that will enumerate all the
files in the timezone directory. The WHERE clause doesn't apply until after
the function has already traversed all files.

> As you can see, the execution of that single fetch dwarfs all other
> processing loads. I've run this a few times, and the timings are always
> roughly the same. Is there a way for me to speed this up? Would I be
> better off loading these into a static table and executing from there?

Yes, much better if it's something you're querying regularly.

//Magnus