Re: Change default of checkpoint_completion_target

On 1/19/21 2:47 PM, Stephen Frost wrote:
> 
> * Tom Lane (tgl@sss.pgh.pa.us) wrote:
>> Stephen Frost <sfrost@snowman.net> writes:
>>> Any further comments or thoughts on this one?
>>
>> This:
>>
>> +        total time between checkpoints. The default is 0.9, which spreads the
>> +        checkpoint across the entire checkpoint timeout period of time,
>>
>> is confusing because 0.9 is obviously not 1.0; people will wonder
>> whether the scale is something strange or the text is just wrong.
>> They will also wonder why not use 1.0 instead.  So perhaps more like
>>
>>     ... The default is 0.9, which spreads the checkpoint across almost
>>     all the available interval, providing fairly consistent I/O load
>>     while also leaving some slop for checkpoint completion overhead.
>>
>> The other chunk of text seems accurate, but there's no reason to let
>> this one be misleading.
> 
> Good point, updated along those lines.

I had a look at the patch and the change and new documentation seem 
sensible to me.

I think this phrase may be a bit too idiomatic:

+        consistent I/O load while also leaving some slop for checkpoint

Perhaps just:

+        consistent I/O load while also leaving some time for checkpoint

It seems to me that the discussion about changing the wording for GUCs 
not changeable after server should be saved for another patch as long as 
this patch follows the current convention.

Regards,
-- 
-David
david@pgmasters.net