Re: O_DIRECT in freebsd

Sean Chittenden <sean(at)chittenden(dot)org> writes:
>> it doesn't seem totally out of the question. I'd kinda like to see
>> some experimental evidence that it's worth doing though. Anyone
>> care to make a quick-hack prototype and do some measurements?

> What would you like to measure? Overall system performance when a
> query is using O_DIRECT or are you looking for negative/postitve
> impact of read() not using the FS cache? The latter is much easier to
> do than the former... recreating a valid load environment that'd let
> any O_DIRECT benchmark be useful isn't trivial.

If this stuff were easy, we'd have done it already ;-). The first
problem is to figure out what makes sense to measure.

Given that the request is for a quick-and-dirty test, I'd be willing to
cut you some slack on the measurement process. That is, it's okay to
pick something easier to measure over something harder to measure, as
long as you can make a fair argument that what you're measuring is of
any interest at all...

regards, tom lane