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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