Re: Experimental patch for inter-page delay in VACUUM

Jan Wieck <JanWieck(at)Yahoo(dot)com> writes:
> Tom Lane wrote:
>> I have never been happy with the fact that we use sync(2) at all.

> Sure does it do too much. But together with the other layer of
> indirection, the virtual file descriptor pool, what is the exact
> guaranteed behaviour of
> write(); close(); open(); fsync();
> cross platform?

That isn't guaranteed, which is why we have to use sync() at the
moment. To go over to fsync or O_SYNC we'd need more control over which
file descriptors are used to issue writes. Which is why I was thinking
about moving the writes to a centralized writer process.

>> Actually, once you build it this way, you could make all writes
>> synchronous (open the files O_SYNC) so that there is never any need for
>> explicit fsync at checkpoint time.

> Yes, but then the configuration leans more towards "take over the RAM"

Why? The idea is to try to issue writes at a fairly steady rate, which
strikes me as much better than the current behavior. I don't see why it
would force you to have large numbers of buffers available. You'd want
a few thousand, no doubt, but that's not a large number.

regards, tom lane