Re: checkpointer continuous flushing

On 2016-01-07 11:27:13 +0100, Fabien COELHO wrote:
> I read your patch and I know what I want to try to have a small and simple
> fix. I must admit that I have not really understood in which condition the
> checkpointer would decide to close a file, but that does not mean that the
> potential issue should not be addressed.

There's a trivial example: Consider three tablespaces and
max_files_per_process = 2. The balancing can easily cause three files
being flushed at the same time.

But more importantly: You designed the API to be generic because you
wanted it to be usable for other purposes as well. And for that it
certainly needs to deal with that.

> Also, I gave some thoughts about what should be done for bgwriter random
> IOs. The idea is to implement some per-file sorting there and then do some
> LRU/LFU combing. It would not interact much with the checkpointer, so for me
> the two issues should be kept separate and this should not preclude changing
> the checkpointer, esp. given the significant performance benefit of the
> patch.

Well, the problem is that the patch significantly regresses some cases
right now. So keeping them separate isn't particularly feasible.

Greetings,

Andres Freund