Re: [ldap] slapd eating CPU after query returning many matches

["Kurt D. Zeilenga" <Kurt@Boolean.Net>]

This patch has been committed to -devel...

Kurt D. Zeilenga wrote:
> 
> Tom,
> 
> Thanks, I've forward it to the development list for discussion.
> 
> Kurt
> 
> Tom Ivar Helbekkmo wrote:
> >
> > I wrote:
> >
> > > I'm thinking either a select() problem, or a bug related to the fact
> > > that I'm running it on a system with no threads -- probably the
> > > former.
> >
> > Gee, I'm good at this.  ;-)  It turned out to be select() returning
> > immediately, because running without threads shows up a problem with
> > the handling of the "active_threads" counter in slapd.
> >
> > In the function send_search_entry() in result.c, the call to
> > ber_flush() fails many times in the course of the shipping out of a
> > large number of matches, each time with an EAGAIN.  This causes
> > active_threads to be decremented each time, so it ends up with a
> > large, negative value.  Over in daemon.c, the non-zero value of
> > active_threads causes select() to be called with a zero timeout.
> >
> > Unfortunately, just adding a test for > 0 to the decrementing did not
> > fix it, because active_threads then ends up with the value 1 after the
> > large transaction.  I haven't tried to figure out why, I've only done
> > the following to daemon.c:
> >
> > Index: daemon.c
> > ===================================================================
> > RCS file: /repo/OpenLDAP/pkg/ldap/servers/slapd/daemon.c,v
> > retrieving revision 1.11
> > diff -r1.11 daemon.c
> > 222c222
> > < #ifdef PTHREAD_PREEMPTIVE
> > ---
> > > #if defined(PTHREAD_PREEMPTIVE) || defined(NO_THREADS)
> >
> > This causes a NULL value to be used for the timeout parameter to
> > select() every time, which is what we want when running without
> > threads anyway.  Of course, this is not necessarily a real fix: the
> > fact that the problem occurs may indicate that there is a flaw in the
> > logic around active_threads that could cause problems even when the
> > code is built with a threads library, given the right circumstances.
> >
> > Works for me, though.  :-)
> >
> > -tih
> > --
> > Popularity is the hallmark of mediocrity.  --Niles Crane, "Frasier"