Re: [HACKERS] Overhauling GUCS

[Decibel!]

On Jun 11, 2008, at 9:34 PM, Bruce Momjian wrote:

Tom Lane wrote:

Bruce Momjian <[EMAIL PROTECTED]> writes:

Tom Lane wrote:

The idea has a fundamental logical flaw, which is that it's not clear

which parameter wins if the user changes both.

Yes, you could get into problems by having variable dependency loops,

during
        set memory_usage = X;  // implicitly sets work_mem = X/100, say
        set work_mem = Y;
        set memory_usage = Z;

Who said anything about loops? What I am talking about is what happens

My initial thought was that this would behave like a shell script

to it below in postgresql.conf.  The problem with that is that we

have in a shell script.

I was not thinking of memory_usage implicity changing anything.  I
figured postgresql.conf would have:

        memory_usage = 100
        work_mem = $memory_usage * 0.75

If you change memory_usage via SET, it will not change work_mem at all
because you are not re-initializing the variables.

variable, meaning once you set something it would affect all references comment out all settings, so there isn't a logical order like you would

Why? That's the exact opposite of what I'd expect. If I want a setting's value to be $memory_usage * .75, that's what I want it to be. Not some value based on whatever $memory_usage was set to when work_mem happened to be changed. Of course, if you set something to a hard value with no variables, then that's what it's set to.

I am kind of lost how this would work logically and am willing to think

about it some more, but I do think we aren't going to simplify
postgresql.conf without such a facility.

Agreed. And I think it's a lot more elegant for dealing with day-to- day tuning than some kind of external wizzard.

The big problem I see is that right now everything has a constant

would we signal that we want the variables based on it to change their
values?  This is your behind-the-scenes problem you mentioned.

default. If we allowed memory_usage to change some of the defaults, how

--
Decibel!, aka Jim C. Nasby, Database Architect  [EMAIL PROTECTED]
Give your computer some brain candy! www.distributed.net Team #1828

I would suggest that we just re-evaluate everything whenever any setting is changed (this assumes that we store postgresql.conf internally in some fashion, so that we're not actually hitting the file all the time and possibly picking up random edits).

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