Re: Experimental patch for inter-page delay in VACUUM

Bruce Momjian wrote:

> Jan Wieck wrote:
>> Zeugswetter Andreas SB SD wrote:
>>
>> >> > One problem with O_SYNC would be, that the OS does not group writes any
>> >> > more. So the code would need to eighter do it's own sorting and grouping
>> >> > (256k) or use aio, or you won't be able to get the maximum out of the disks.
>> >>
>> >> Or just run multiple writer processes, which I believe is Oracle's
>> >> solution.
>> >
>> > That does not help, since for O_SYNC the OS'es (those I know) do not group those
>> > writes together. Oracle allows more than one writer to busy more than one disk(subsystem) and circumvent other per process limitations (mainly on platforms without AIO).
>>
>> Yes, I think the best way would be to let the background process write a
>> bunch of pages, then fsync() the files written to. If one tends to have
>> many dirty buffers to the same file, this will group them together and
>> the OS can optimize that. If one really has completely random access,
>> then there is nothing to group.
>
> Agreed. This might force enough stuff out to disk the checkpoint/sync()
> would be OK. Jan, have you tested this?
>

As said, not using fsync() but sync() at that place. This only makes a
real difference when you're not running PostgreSQL on a dedicated
server. And yes, it really works well.

Jan

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