Re: max_standby_delay considered harmful

On Mon, 2010-05-03 at 22:45 -0400, Bruce Momjian wrote:

> As I remember, 9.0 has two behaviors:
> 
>     o  master delays vacuum cleanup
>     o  slave delays WAL application
> 
> and in 9.1 we will be adding:
> 
>     o  slave communicates snapshots to master

> How would this figure into what we ultimately want in 9.1?

We would still want all options, since "slave communicates snapshot to
master" doesn't solve the problem it just moves the problem elsewhere.
It's a question of which factors the user wishes to emphasise for their
specific use.

> I understand Simon's point that the two behaviors have different
> benefits.  However, I believe few users will be able to understand when
> to use which.

If users can understand how to set NDISTINCT for a column, they can
understand this. It's not about complexity of UI, its about solving
problems. When people hit an issue, I don't want to be telling people
"we thought you wouldn't understand it, so we removed the parachute".
They might not understand it *before* they hit a problem, so what? But
users certainly will afterwards and won't say "thanks" if you prevent an
option for them, especially for the stated reason. (My point about
ndistinct: 99% of users have no idea that exists or when to use it, but
it still exists as an option because it solves a known issue, just like
this.)

-- Simon Riggs           www.2ndQuadrant.com