New FreeBSD 5.3 e-mail server extremely slow - traced to getpwnam maybe ?

[Bruce Campbell]

Quoting Kris Kennaway <kris at obsecurity.org>:

> On Tue, Jan 04, 2005 at 09:27:27PM -0500, Bruce Campbell wrote:
> 
> > I wrote a small program:
> > 
> >   #include <sys/types.h>
> >   #include <pwd.h>
> > 
> >   main( int argc, char *argv[] )
> >   {
> >   getpwuid( 13076 );
> >   }
> > 
> > and ran it under truss on 5.x and it generated 178,711 lines of output.
> > (the bulk of which is those lseek/read calls as above)
> > ...
> 
> Try tuning the pwd_mkdb parameters (see hash(3)) in
> /usr/src/usr.sbin/pwd_mkdb/pwd_mkdb.c and recompile:
> 
> HASHINFO openinfo = {
>         4096,           /* bsize */
>         32,             /* ffactor */
>         256,            /* nelem */
>         2048 * 1024,    /* cachesize */
>         NULL,           /* hash() */
>         0               /* lorder */
> };
> 
> e.g. adjust nelem to 12000 to accomodate your
> significantly-larger-than-average password database.  If this helps,
> please submit a PR requesting that someone make an option to pwd_mkdb
> to tune this at runtime (or better yet, submit the patch to do this
> yourself - it's straightforward to modify the source to do this).

Thanks.  That had no effect on the large number of seeks/reads
to do a getpwuid of a specific uid.  I tried boosting that
number further, still no change.  I suspect the problem is related
to some change to the hash functions between 4.7 and 5.2.1 and I
hope to get to the bottom of it today.

I tried two getpwnam (as opposed to getpwuid) calls on 2 different userids, one
took 1000 seek/reads, the other 16,000, so it's all
pretty random, no doubt related to how stuff gets hashed.  On
4.7 it takes just one or two reads/seeks.

As each login via ipop, imap, and each sendmail, and just about everything
will be doing getpwnam's I think this is our problem.

-- 
Bruce Campbell
Engineering Computing
CPH-2374B
University of Waterloo
(519)888-4567 ext 5889

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