Re: Revisiting disk layout on ZFS systems

On 4/29/2014 3:13 AM, Albe Laurenz wrote:
> Karl Denninger wrote:
>> I've been doing a bit of benchmarking and real-world performance
>> testing, and have found some curious results.
> [...]
>
>> The odd thing is that I am getting better performance with a 128k record
>> size on this application than I get with an 8k one!
> [...]
>
>> What I am curious about, however, is the xlog -- that appears to suffer
>> pretty badly from 128k record size, although it compresses even
>> more-materially; 1.94x (!)
>>
>> The files in the xlog directory are large (16MB each) and thus "first
>> blush" would be that having a larger record size for that storage area
>> would help. It appears that instead it hurts.
> As has been explained, the access patterns for WAL are quite different.
>
> For your experiment, I'd keep them on different file systems so that
> you can tune them independently.
>
They're on physically-different packs (pools and groups of spindles) as
that has been best practice for performance reasons pretty-much always
-- I just thought it was interesting, and worth noting, that the usual
recommendation to run an 8k record size for the data store itself may no
longer be valid.

It certainly isn't with my workload.

--
-- Karl
karl(at)denninger(dot)net