Re: Bgwriter strategies

On Fri, 6 Jul 2007, Heikki Linnakangas wrote:

> There's something wrong with that. The number of buffer allocations shouldn't 
> depend on the bgwriter strategy at all.

I was seeing a smaller (closer to 5%) increase in buffer allocations 
switching from no background writer to using the stock one before I did 
any code tinkering, so it didn't strike me as odd.  I believe it's related 
to the TPS numbers.  When there are more transactions being executed per 
unit time, it's more likely the useful blocks will stay in memory because 
their usage_count is getting tickled faster, and therefore there's less of 
the most useful blocks being swapped out only to be re-allocated again 
later.

Since the bad bgwriter tunings reduce TPS, I believe that's the mechanism 
by which there are more allocations needed.  I'll try to keep an eye on 
this now that you've brought it up.

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