directio question

[Igor Sysoev]

On Sun, Mar 07, 2010 at 08:07:13PM +0200, Stefan Parvu wrote:

> Hi,
> 
> My name is Stefan Parvu, Im working on http://www.systemdatarecorder.org
> and I have started to test and consider replacing for our solution 
> apache over nginx. Im getting to know nginx and I like the server.
> 
> Some question reading over http://wiki.nginx.org/NginxHttpCoreModule
> about DirectIO:
> 
> "The directive enables use of flags O_DIRECT (FreeBSD, Linux), 
> F_NOCACHE (Mac OS X) or directio() function (Solaris) for reading 
> files with size greater than specified. This directive disables 
> use of sendfile for this request." 
> 
> DirectIO in Solaris is a feature, when enabled lets you to bypass entirely the
> OS's page cache and read/write directly from/to disk. This has some
> benefits where workloads are database servers and you want to avoid
> double caching. 
> 
> Im a bit curious under what situations would like to have DirectIO enabled on
> nginx and are we talking about same thing when we refer to directio ?
>  http://www.solarisinternals.com/wiki/index.php/Direct_I/O
> 
> Usually most applications will benefit of having the OS's page cache involved 
> rather of going to disk. 

Yes, nginx's directio is what you have said. It may or may not improve
perfomance of serving large files when a server physical memory is much
less than summary size of the files.


-- 
Igor Sysoev
http://sysoev.ru/en/