Re: data on devel code perf dip

On Thu, Aug 11, 2005 at 09:02:03PM -0400, Tom Lane wrote:

> I am sure I will get some pushback if I propose reverting the O_DIRECT
> patch, so could you try to get some more-specific evidence?  Like pull
> the CVS tree from just before and just after this patch and compare
> performance?

Quoth the open(2) manpage:
      O_DIRECT             Try to minimize cache effects of the I/O to  and  from  this             file.   In  general this will degrade performance, but it is             useful in special situations, such as when  applications  do             their  own  caching.  File I/O is done directly to/from user             space buffers.  The I/O is synchronous, i.e., at the comple-             tion of the read(2) or write(2) system call, data is guaran-             teed to have been transferred.

In light of this, may I ask whether it makes sense to compare the
performance of two runs with similar shared_buffer settings?  With
O_DIRECT, I understand from this manpage that the OS is going to do
little or no page caching, so shared_buffers should be increased to
account for this fact.

Am I missing something?

-- 
Alvaro Herrera ()
"Hay que recordar que la existencia en el cosmos, y particularmente la
elaboración de civilizaciones dentre de él no son, por desgracia,
nada idílicas" (Ijon Tichy)