Re: Log levels for checkpoint/bgwriter monitoring

On Fri, 9 Mar 2007, Jim Nasby wrote:

> I'm wondering if pg_bench is a good test of this stuff. ISTM it's 
> unrealistically write-heavy, which is going to tend to not only put a 
> lot of dirty buffers into the pool, but also keep them pinned enough 
> that you can't write them.

Whether it's "unrealistically" write-heavy kind of depends on what your 
real app is.  The standard pgbench is a bit weird because it does so many 
updates to tiny tables, which adds a level of locking contention that 
doesn't really reflect many real-world situations.  But the no-branch mode 
(update/select to accounts, insert into history) isn't too dissimilar from 
some insert-heavy logging applications I've seen.

The main reason I brought this all up was because Itagaki seemed to be 
using pgbench for some of his performance tests.  I just wanted to point 
out that the LRU background writer specifically tends to be very 
underutilized when using pgbench.

--
* Greg Smith gsmith@gregsmith.com http://www.gregsmith.com Baltimore, MD