Re: Proposal: backend "niceness" / session_priority

On 7/30/15 10:54 AM, Tom Lane wrote:

José Luis Tallón <jltallon@adv-solutions.net> writes:

      Since PostgreSQL lacks the resource management capabilities of the
"Big Ones" ( Resource Groups - Red, WorkLoad Manager - Blue ) or the
Resource Governor in MS SQL Server, we can try and approximate the
requested behaviour by reducing the CPU priority ("nice") of the backend
in question. Please note that we would be using scheduler priority to
try and modulate I/O, though I'm aware of the limitations of this mechanism.

This has been proposed before, and rejected before, and I'm not seeing
anything particularly new here.  Without a credible mechanism for
throttling I/O, "nice" alone does not seem very promising.

Some OSes respect nice when it comes to IO scheduling, so it might still be useful. What I'm worried about is priority inversion[1].

What might be useful would be to add a set of GUCs similar to vacuum_cost_* that operated at the shared buffer level. Dunno where you'd put the sleep though (presumably all the functions where you'd put the accounting are too low-level to sleep in).