Intro / Busy loop and blocking threads on 1.2.5

[Miguel DeAvila]

On Wednesday 07 May 2008 14:37:16 Michael D'Agosta wrote:
> Haven't tried the patch yet (waiting on my app changes to crash :) ), and am 
> beginning to read through assoc.c, naively wondering if the lookahead patch will 
> work as expected. If I understand right, both the lookahead and it pointers are 
> moving targets, and would only detect local loops 2 deep. Wouldn't you want to 
> save an orig for comparing to lookahead?

I went down this road myself ... the trick is that the lookahead pointer increments
two items for every since increment of the it pointer. If a loop exists then the lookahead
pointer will eventually wrap around and catch up with the it pointer.

> 
> Do you have a real-time communication mechanism, like IRC? This kind of thing 
> might be easier done there.
> 
> You know, I haven't tried the 64bit compile-time option, and I'm trying to use a 
> large amount of memory (8GB). What is the effect of compiling with the 64bit 
> option?
> 
> Thanks,
> -Michael
> 
> dormando wrote:
> > Sorry to hear :\
> > 
> > Well, hold tight for now.
> > 
> > Info for the list: This is likely another case of the assoc_find bug.
> > We're putting all bughunting resources into tracking it down right now.
> > Hopefully we will have a fix soon, and I will be sending more info to
> > the list to help out as soon as I can.
> > 
> > The bug's in assoc.c somewhere - Something causes the linked lists to
> > have a loop.
> > 
> > Michael; Check the archives a few days back for a post from trond norbye
> > with a patch for detecting and bombing out on such loops. If you try
> > that out it could help us narrow things down.
> > 
> > We've otherwise been completely unable to reproduce the bug outside of
> > the wild.
> > 
> > Thanks,
> > -Dormando
> > 
> > Michael D'Agosta wrote:
> >> The latter - both pegging the CPU and not accepting new connections.
> >> This only happens every couple of days, but I can notice any other
> >> symptoms that are relevant...
> >>
> >> -MD
> >>
> >> dormando wrote:
> >>> Hey,
> >>>
> >>> Is memcached simply not accepting new connections and idling, or is it
> >>> pegging the CPU and not accepting new connections?
> >>>
> >>> -Dormando
> >>>
> >>> Michael D'Agosta wrote:
> >>>> Hello,
> >>>>
> >>>> New to the list - hi people. I was reading a thread from April:
> >>>>   http://lists.danga.com/pipermail/memcached/2008-April/006683.html
> >>>>
> >>>> It seems that during busy times, one of our memcached instances will
> >>>> stop accepting new connections; when I run telnet host port, I don't get
> >>>> a prompt. It's MC 1.2.5 on CentOS 4.6 w/ libevent 1.1a. We didn't
> >>>> compile in threading before, so I'm giving that a test drive as I type.
> >>>>
> >>>> Did anyone discover solutions or workarounds to the problem?
> >>>>
> >>>> Thanks in advance,
> >>>>
> >>>> Mike
> > 
>