Re: Auto-tuning work_mem and maintenance_work_mem

On Wed, Oct  9, 2013 at 01:34:21PM -0400, Robert Haas wrote:
> And quite frankly I don't think I really believe the auto-tuning
> formula has much chance of being right in the first place.  It's
> generally true that you're going to need to increase work_mem if you
> have more memory and decrease it work_mem if you have more
> connections, but it also depends on a lot of other things, like the
> complexity of the queries being run, whether all of the connection
> slots are actually routinely used, and whether you've really set
> shared_buffers to 25% of your system's total memory, which many people
> do not, especially on Windows.  I think we're just going to create the
> false impression that we know what the optimal value is when, in
> reality, that's far from true.

I disagree.  There is nothing preventing users from setting their own
values, but I think auto-tuning will be make people who don't change
values more likely to be closer to an optimal values.  We can't
auto-tune to a perfect value, but we can auto-tune closer to a perfect
value than a fixed default.  Yes, auto-tuned values are going to be
worse for some users, but I believe they will be better for most users.

Having really bad defaults so everyone knows they are bad really isn't
user-friendly because the only people who know they are really bad are
the people who are tuning them already.  Again, we need to think of the
typical user, not us.

--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
 + Everyone has their own god. +