Re: checkpointer continuous flushing

On 2016-01-09 19:05:54 +0530, Amit Kapila wrote:
> Right that won't be acceptable, however I think with your latest
> proposal [1]

Sure, that'd address that problem.


> [...] think that idea will help to mitigate the problem of backend and
> bgwriter writes as well.  In that, can't we do it with the help of
> existing infrastructure of *pendingOpsTable* and
> *CheckpointerShmem->requests[]*, as already the flush requests are
> remembered in those structures, we can use those to apply your idea to
> issue flush requests.

Hm, that might be possible. But that might have some bigger implications
- we currently can issue thousands of flush requests a second, without
much chance of merging. I'm not sure it's a good idea to overlay that
into the lower frequency pendingOpsTable. Backends having to issue
fsyncs because the pending fsync queue is full is darn expensive. In
contrast to that a 'flush hint' request getting lost doesn't cost that
much.

Greetings,

Andres Freund