Re: Controlling Load Distributed Checkpoints

Heikki Linnakangas <heikki(at)enterprisedb(dot)com> writes:
> Tom Lane wrote:
>> I don't think it's a historical artifact at all: it's a valid reflection
>> of the fact that we don't know enough about disk layout to do low-level
>> I/O scheduling. Issuing more fsyncs than necessary will do little
>> except guarantee a less-than-optimal scheduling of the writes.

> I'm not proposing to issue any more fsyncs. I'm proposing to change the
> ordering so that instead of first writing all dirty buffers and then
> fsyncing all files, we'd write all buffers belonging to a file, fsync
> that file only, then write all buffers belonging to next file, fsync,
> and so forth.

But that means that the I/O to different files cannot be overlapped by
the kernel, even if it would be more efficient to do so.

regards, tom lane