Re: Clock sweep not caching enough B-Tree leaf pages?

On Thu, Apr 17, 2014 at 1:39 PM, Andres Freund <andres@2ndquadrant.com> wrote:
> On 2014-04-17 13:33:27 -0700, Peter Geoghegan wrote:
>> Just over 99.6% of pages (leaving aside the meta page) in the big 10
>> GB pgbench_accounts_pkey index are leaf pages.
>
> That's a rather nice number. I knew it was big, but I'd have guessed
> it'd be a percent lower.

Yes, it's usually past 99.5% for int4. It's really bad if it's as low
as 96%, and I think that often points to what are arguably bad
indexing choices, like indexing text columns that have long text
strings.

> Do you happen to have the same stat handy for a sensibly wide text or
> numeric real world index? It'd be interesting to see what the worst case
> there is.

Yes, as it happens I do:
http://www.postgresql.org/message-id/CAM3SWZTcXrdDZSpA11qZXiyo4_jtxwjaNdZpnY54yjzq7d64=A@mail.gmail.com

I was working of my Mouse Genome database, which is actually
real-world data use by medical researchers, stored in a PostgreSQL
database by those researchers and made available for the benefit of
other medical researchers.

-- 
Peter Geoghegan