rack-devel archive mirror (unofficial) https://groups.google.com/group/rack-devel
 help / color / mirror / code / Atom feed
From: James Tucker <jftucker@gmail.com>
To: rack-devel@googlegroups.com
Subject: Re: Session collisions on rails 3.1rc4 (authlogic, omniauth, memcache store, passenger)
Date: Thu, 4 Aug 2011 16:26:11 -0700	[thread overview]
Message-ID: <BE9DB04C-5F0E-4F50-9436-C736BE0D9C9C@gmail.com> (raw)
In-Reply-To: <2CD439944A9549FA982EC7D0A8A85EA0@gmail.com>

[-- Attachment #1: Type: text/plain, Size: 3564 bytes --]

Maybe once I've had time to do a proper review.

On Aug 3, 2011, at 3:32 AM, Joshua Ballanco wrote:

> Hi Neil,
> Good to hear you figured that out. I, too, had heard mention of Dalli as a replacement for memcache-client. Perhaps we should update Rack's gemspec?
> - Josh
> On Thursday, July 28, 2011 at 10:54 PM, Neil Matatall wrote:
>> Joshua,
>> I think what you described was indeed our issue. The call to @pool.add
>> actually returned "END" which is a sign of a get_multikey
>> We were using memcache-client and the author informed me that the
>> project was no longer supported and said that this can occur when the
>> same memcache instance handles sessions and data. He recommended
>> splitting the caches as well as switching to Dalli instead.
>> So...not a rack issue!
>> Thanks!
>> Neil
>> On 7/25/11 1:23 PM, Joshua Ballanco wrote:
>>> Have you considered the possibility that memcache might be recycling
>>> keys on you?
>>> We had an issue a while back where we were using memcache for both
>>> fragment caching and session storage. Occasionally, we would get
>>> exceptions in retrieving a session, and looking at the error message
>>> it was clear that what was retrieved from memcache was a fragment and
>>> not a session. Unfortunately, we moved back to a cookie-based session
>>> store before we had a chance to look deeper into the issue. What I can
>>> say is that based on the key generation scheme we were using for
>>> sessions and cache keys, there was effectively 0 chance that we were
>>> duplicating keys. Instead, it seemed like memcache was re-using slots
>>> for different keys when we started exhausting free slots.
>>> Hope that helps!
>>> - Joshua Ballanco
>>> On Monday, July 25, 2011 at 2:22 PM, Neil wrote:
>>>> While it's entirely possible that this issue is caused by some other
>>>> factor, but we are getting session collisions as well as an issue
>>>> where one user is getting another user's session. This is clearly
>>>> bad, but I cannot for the life of me figure out how this could even
>>>> happen in the first place. The code looks thread safe to me, and a
>>>> quick discussion on #ruby-lang seems to support that.
>>>> Thoughts:
>>>> 1. Session IDs are being generated in the same sequence (uses
>>>> securerandom -> openssl which does not have a static seed)
>>>> 2. Threads. Looks good to me.
>>>> 3. Maybe memcached is returning something other than "STORED/
>>>> NOT_STORED" for @pool.add(sid, session), but the operation still
>>>> succeeded?
>>>> 4. Gnomes.
>>>> Any input is GREATLY appreciated. Please don't say "it's an RC, what
>>>> do you expect?" :)
>>>> From
>>>> https://github.com/rack/rack/blob/master/lib/rack/session/memcache.rb
>>>> def generate_sid
>>>> loop do
>>>> sid = super
>>>> break sid unless @pool.get(sid, true)
>>>> end
>>>> end
>>>> def get_session(env, sid)
>>>> with_lock(env, [nil, {}]) do
>>>> unless sid and session = @pool.get(sid)
>>>> sid, session = generate_sid, {}
>>>> unless /^STORED/ =~ @pool.add(sid, session)
>>>> raise "Session collision on '#{sid.inspect}'"
>>>> end
>>>> end
>>>> [sid, session]
>>>> end
>>>> end
>>>> def set_session(env, session_id, new_session, options)
>>>> expiry = options[:expire_after]
>>>> expiry = expiry.nil? ? 0 : expiry + 1
>>>> with_lock(env, false) do
>>>> @pool.set session_id, new_session, expiry
>>>> session_id
>>>> end
>>>> end

[-- Attachment #2: Type: text/html, Size: 4290 bytes --]

      reply	other threads:[~2011-08-04 23:26 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-07-25 18:22 Neil
2011-07-25 20:23 ` Joshua Ballanco
2011-07-25 21:12   ` Neil Matatall
2011-07-28 19:54   ` Neil Matatall
2011-08-03 10:32     ` Joshua Ballanco
2011-08-04 23:26       ` James Tucker [this message]

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-list from there: mbox

  Avoid top-posting and favor interleaved quoting:

  List information: https://groups.google.com/group/rack-devel

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=BE9DB04C-5F0E-4F50-9436-C736BE0D9C9C@gmail.com \
    --to=rack-devel@googlegroups.com \


* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
Code repositories for project(s) associated with this inbox:


This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).