Re: Experimental patch for inter-page delay in VACUUM

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
processlimitations (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?

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