Re: Should we cacheline align PGXACT?

Alexander Korotkov wrote:

> Yes, influence seems to be low. But nevertheless it's important to insure
> that there is no regression here.
> Despite pg_prewarm'ing and running tests 300s, there is still significant
> variation.
> For instance, with clients count = 80:
> * pgxact-result-2.txt – 474704
> * pgxact-results.txt – 574844
> Could some background processes influence the tests? Or could it be
> another virtual machine?
> Also, I wonder why I can't see this variation on the graphs.
> Another issue with graphs is that we can't see details of read and write
> TPS variation on the same scale, because write TPS values are too low. I
> think you should draw write benchmark on the separate graph.

So, I'm reading that on PPC64 there is no effect, and on the "lesser"
machine Tomas tested on, there is no effect either; this patch only
seems to benefit Alexander's 72 core x86_64 machine.

It seems to me that Andres comments here were largely ignored:
https://www.postgresql.org/message-id/20160822021747.u5bqx2xwwjzac5u5@alap3.anarazel.de
He was suggesting to increase the struct size to 16 bytes rather than
going all the way up to 128. Did anybody test this?

Re the coding of the padding computation, seems it'd be better to use
our standard "offsetof(last-struct-member) + sizeof(last-struct-member)"
rather than adding each of the members' sizes individually.

--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services