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Re: Load Distributed Checkpoints, take 3

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Heikki Linnakangas <heikki(at)enterprisedb(dot)com>
Cc: Patches <pgsql-patches(at)postgresql(dot)org>
Subject: Re: Load Distributed Checkpoints, take 3
Date: 2007-06-21 13:52:54
Message-ID: 15575.1182433974@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-patches
Heikki Linnakangas <heikki(at)enterprisedb(dot)com> writes:
> Tom Lane wrote:
>> I tend to agree with whoever said upthread that the combination of GUC
>> variables proposed here is confusing and ugly.  It'd make more sense to
>> have min and max checkpoint rates in KB/s, with the max checkpoint rate
>> only honored when we are predicting we'll finish before the next
>> checkpoint time.

> Really? I thought everyone is happy with the current combination, and 
> that it was just the old trio of parameters controlling the write, nap 
> and sync phases that was ugly. One particularly nice thing about 
> defining the duration as a fraction of checkpoint interval is that we 
> can come up with a reasonable default value that doesn't depend on your 
> hardware.

That argument would hold some water if you weren't introducing a
hardware-dependent min rate in the same patch.  Do we need the min rate
at all?  If so, why can't it be in the same units as the max (ie, a
fraction of checkpoint)?

> How would a min and max rate work?

Pretty much the same as the code does now, no?  You either delay, or not.

			regards, tom lane

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Subject: Re: Load Distributed Checkpoints, take 3
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