first time user with out of memory question

[Paul T]

--- Nikolas Coukouma <atrus at atrus.org> wrote:

> Paul T wrote:
> > --- Ivan Krstic <krstic at fas.harvard.edu> wrote:
> >
> >> Paul T wrote:
> >>>  You're right. What is implemented in memcached
> >> should
> >>> be called "Lazy Garbage Collection".
> >> No, it shouldn't. Memcached doesn't do GC. It
> does
> >> LRU ejection.
> >
> >  Unfortunately, as per google, such a thing exists
> > only in your head :
> >
> >
>
http://www.google.com/search?hl=en&lr=&q=%22LRU+ejection%22&btnG=Search
> LRU is "Least Recently Used" and it's a basic
> algorithm. I'll grant that
> the verb used is usually "eviction", not "ejection"
> 
> http://en.wikipedia.org/wiki/Least_recently_used
>
http://en.wikipedia.org/wiki/Page_replacement_algorithms#Least_Recently_Used

LRU eviction means "Last Recently Used item is
evicted". This is very general concept. I was talking
about the implementation of the "eviction" in
memcached and I called it "mark and sweep". 

How would you call the memcached implementation of LRU
eviction?
 
> >>> Unfortunately, memcached is an asynchronous
> >>> application (based on libevent).
> >> How is this unfortunate?
> >
> >  For example, because one can not apply automated
> > tools, such as valgrind, to debug such an
> application.
> I can see how it's more difficult, but certainly not
> impossible. 

Close to impossible, actually.

> I just
> ran it under valgrind massif and memcheck. The only
> problematic thing
> was the maximum number of connections

Exactly ;-) It starts to timeout under IRL pressure,
so some things would not bite you under valgrind (but
will kill you IRL).

>  which I had
> to drop. Is there
> something I'm missing?
> 
> Valgrind memcheck did produce some interesting
> results on
> memcached-1.1.13-pre:
> 
> ==12723== Conditional jump or move depends on
> uninitialised value(s)

Now we are talking. There is a bug that *may* show
itself under pressure (timings). 

I think that nobody on this list is running memcached
under heavy pressure, though, so this bug can be 
happily ignored in many cases.

Thanks for the sane reaction.

Rgds.Paul.

> ==12723==    at 0x804BA8E: drive_machine
> (memcached.c:1228)
> ==12723==    by 0x4052740: event_base_loop
> (event.c:256)
> ==12723==    by 0x40529F8: event_loop (event.c:305)
> ==12723==    by 0x804CF9D: main (memcached.c:1740)
> ==12723==
> ==12723== Conditional jump or move depends on
> uninitialised value(s)
> ==12723==    at 0x804BF84: drive_machine
> (memcached.c:1206)
> ==12723==    by 0x4052740: event_base_loop
> (event.c:256)
> ==12723==    by 0x40529F8: event_loop (event.c:305)
> ==12723==    by 0x804CF9D: main (memcached.c:1740)
> ==12723==
> ==12723== Conditional jump or move depends on
> uninitialised value(s)
> ==12723==    at 0x804BF0D: drive_machine
> (memcached.c:1248)
> ==12723==    by 0x4052740: event_base_loop
> (event.c:256)
> ==12723==    by 0x40529F8: event_loop (event.c:305)
> ==12723==    by 0x804CF9D: main (memcached.c:1740)


 
> Cheers,
> -Nikolas
> 
> 


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