Re: MMAP Buffers

Joshua Berkus <josh@agliodbs.com> Friday 15 April 2011 18:55:04
> Radoslaw,
> 
> 10% improvement isn't very impressive from a switch to mmap.  What workload
> did you test with?  What I'd really like to see is testing with databases
> which are 50%, 90% and 200% the size of RAM ... that's where I'd expect
> the greatest gain from limiting copying.
I think 10% is quite good, as my stand-alone test of mmap vs. read shown that 
speed up of copying 100MB data to mem may be from ~20ms to ~100ms (depends on 
destination address). Of course deeper, system test simulating real usage will 
say more. In any case after good deals with writes, I will speed up reads. I 
think to bypass smgr/md much more and to expose shared id's (1,2,3...) for 
each file segment.

Going to topic...

In attachment I sent test-scripts which I used to fill data, nothing complex 
(left from 2nd level caches).

Query I've used to measure was SELECT count(substr(content, 1, 1)) FROM 
testcase1 WHERE multi_id > 50000;

Timings ware taken from psql.

I didn't made load (I have about 2GB of free sapce at /home, and 4GB RAM) and 
stress (I'm not quite ready to try concurrent updates of same page - may fail, 
notice is and place to fix is in code) tests yet.

> > Netbeans is possibly not very well suited to working on postgres code.
> > AFAIK emacs and/or vi(m) are used by almost all the major developers.
> 
> Guys, can we *please* focus on the patch for now, rather than the
> formatting, which is fixable with sed?
Netbeans is quite good, of course it depends who likes what. Just try 7.0 RC 
2.

Regards,
Radek