Re: Load distributed checkpoint

"Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov> wrote:

> We have not experience any increase in I/O, just a smoothing. Keep in
> mind that the file system cache will collapse repeated writes to the
> same location until things settle, and the controller's cache also has a
> chance of doing so. If we just push dirty pages out to the OS as soon
> as possible, and let the file system do its job, I think we're in better
> shape than if we try to micro-manage it within our buffer pages.

Maybe we have two entirely different tuning approaches:
1. Retain dirty buffers in database, and keep OS buffers clean.
2. Keep database clean, and entrust OS to manage dirty buffers.

I suggested the 1st one, and you did the 2nd. Bottle-neck in checkpoints
vary in the approaches; write() will be worse in 1st, fsync() in 2nd.

Distributed write() is easier than distributed fsync(), because we can
use write() on a page basis, but fsync() only on a file basis.
Also, database has own access-frequency information for its buffers,
so I think 1st approach behaves better in handling re-dirty of buffers.

Regards,
---
ITAGAKI Takahiro
NTT Open Source Software Center