Re: reloption to prevent VACUUM from truncating empty pages at the end of relation

On 3/1/19 2:14 PM, Tom Lane wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> I want to make one other point about this patch, which is that over on
>> the thread "New vacuum option to do only freezing" we have a patch
>> that does a closely-related thing. Both patches skip one phase of the
>> overall VACUUM process. THIS patch wants to skip truncation; THAT
>> patch wants to skip index cleanup. Over there, we seem to have
>> settled on DISABLE_INDEX_CLEANUP -- only available as a VACUUM option
>> -- and here I think the proposal is currently VACUUM_SHRINK_ENABLED --
>> only available as a reloption.
>> Now that seems not very consistent.
> Indeed, but I'm not sure that the use-cases are the same. In particular,
> unless somebody has done some rather impossible magic, it would be
> disastrous to apply DISABLE_INDEX_CLEANUP as a reloption, because then
> it would be persistent and you'd never get a real vacuum operation and
> soon your disk would be full. Permanently applying truncation disabling
> seems less insane.
>
> The gratuitously inconsistent spellings should be harmonized, for sure.
>
>

You could allow an explicitly set command option to override the reloption.

It's important for us to be able to control the vacuum phases more. In
particular, the index cleanup phase can have significant system impact
but often doesn't need to be done immediately.

cheers

andrew

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Andrew Dunstan https://www.2ndQuadrant.com
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