"Set" and then "get" don't retrieve the stored value

Brad Fitzpatrick brad at danga.com
Tue Nov 14 16:47:48 UTC 2006

I'm coming into this late.

Why would a "get" right after a "set" not work?  This isn't a known issue,
at least not to me.

If you can reproduce this easily, send me a tcpdump pcap file of the
traffic to your memcached.

If you're using the loopback to a memcached on port 11211, run

# tcpdump -w forbrad.pcap -s 0 -i lo port 11211

Then do your (minimal!) failing test, control-C the tcpdump, and email me
the forbrad.pcap file.

On Tue, 14 Nov 2006, Kristian Hellquist wrote:

> The problem is that the the small window unfortunately seems to be
> quite large for me. Do you have measure in time of how small the
> window is?
> Basically, I have some unit tests on a web application. The web
> application relies on memcached heavily. Everything with memcached has
> worked like a charm for us so far. We cache sql-finders in memcached
> and invalidates the sql-finders when the model has changed.
> In a specific use-case we dont want to update the state of the db
> immediately. This data change *a lot*. So when the state of model
> change we will cache the sql-finder in memcache directly and later on
> we flush the change to the db.  It is in this use-case that I have
> experienced the "set" and "get" problem.
> My unit-test successfully ran when I added a sleep call of 0.3 s
> between each memcache-call :/ This is a lot. Is there a way of
> configurate memcached so I experience greater performance?
> I know that the test-environment doesnt mimick the user behavior of
> the webapplication in real use. We use rails and the unit tests
> doensn't involve the webserver at all. So in real life more delay will
> be inserted between each "set" and "get" call. But, can I *trust*
> memcache that data has been stored if I receive a "STORED" response?
> Is just a matter of time before the value can be retrieved again? Or
> is it bad usage of memcache to cache the sql-finders directly and
> later on update the db?
> Thanks for your reply,
> Kristian Hellquist
> 2006/11/14, Jehiah Czebotar <jehiah at gmail.com>:
> > > Basically, yes.  There is a small window where this can happen.  There
> > > have been numerous discussions about it on the list.  Most people note
> > > it with a set and then delete.
> > >
> >
> > tif my memory serves me, the correct order is a delete, set, then a
> > get all for the same key
> >

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