Re: Slow counting on v9.3

[Mehmet Çakoğlu <mehmetcakoglu@xxxxxxxxx>]

Hi Kai, 

You are right, postgresql Count() function is slow, because; It's physically count the rows one by one. 

Other database systems using indexes for counting, but postgresql walk through all rows in multiple transactions with different row states for calculating the real row count. This is about architecture of postgresql. 

If you use WHERE condition on indexed column in your query, this will be much faster. 

Source: http://wiki.postgresql.org/wiki/Slow_Counting

On Mon, Jan 13, 2014 at 11:57 PM, Kai Sellgren <kaisellgren@xxxxxxxxx> wrote:

Hi,

I'm experiecing slow count performance:

SELECT COUNT(*) AS "count"

FROM "NewsArticle"

Takes 210 ms. I've run analyze and vacuum. I'm on 9.3. Here're the stats http://d.pr/i/6YoB

I don't understand why is it that slow. It returns 1 integer, and counts without filters.

This performs quickly:

SELECT reltuples AS count

FROM pg_class

WHERE relname = 'NewsArticle';

But I'd like to add conditions so I don't like the last method.

--

Yours sincerely,
Kai Sellgren