Hi,
On 2013-12-03 10:44:15 -0800, Josh Berkus wrote:
> I don't know where we'll get the resources to implement our own storage,
> but it's looking like we don't have a choice.
As long as our storage layer is a s suboptimal as it is today, I think
it's a purely detractory to primarily blame the kernel.
We
* cannot deal with large shared_buffers, the dirty-buffer scanning is far to expensive. The amount of memory required
forlocks is pretty big, and every backend carries around a pretty huge private array for the buffer pins.
* do not have scalability in pretty damn central datastructures like buffer mapping.
* Our background eviction mechanism doesn't do anything in lots of workloads but increase contention on important data
structures.
* Due to the missing efficient eviction, we synchronously write out data when acquiring a victim buffer most of the
time.That's already bad if you have a kernel buffering your writes, but if you don't...
* Due to the frequency of buffer pins in almost all workloads, our tracking of the importance of individual buffers is
far,far too volatile.
Greetings,
Andres Freund
-- Andres Freund http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training &
Services