Re: Change default of checkpoint_completion_target

On Wed, 20 Jan 2021 at 03:47, Stephen Frost <sfrost(at)snowman(dot)net> wrote:
> Greetings,
>
> * Tom Lane (tgl(at)sss(dot)pgh(dot)pa(dot)us) wrote:
>> Stephen Frost <sfrost(at)snowman(dot)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.
>
> In passing, I noticed that we have a lot of documentation like:
>
> This parameter can only be set in the postgresql.conf file or on the
> server command line.
>
> ... which hasn't been true since the introduction of ALTER SYSTEM. I
> don't really think it's this patch's job to clean that up but it doesn't
> seem quite right that we don't include ALTER SYSTEM in that list either.
> If this was C code, maybe we could get away with just changing such
> references as we find them, but I don't think we'd want the
> documentation to be in an inconsistent state regarding that.
>

I have already mentioned this in [1], however it seems unattractive.

[1] - https://www.postgresql.org/message-id/flat/199703E4-A795-4FB8-911C-D0DE9F51519C%40hotmail.com

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Japin Li.
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