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Bug #58585 Session redundancy doesn't work
Submitted: 2009-03-16 01:36 UTC Modified: 2021-03-25 16:44 UTC
Votes:16
Avg. Score:4.4 ± 0.9
Reproduced:9 of 9 (100.0%)
Same Version:2 (22.2%)
Same OS:-2 (-22.2%)
From: mail at chernousov dot com Assigned: cmb (profile)
Status: Closed Package: memcache (PECL)
PHP Version: 5.2.5 OS: Gentoo Linux
Private report: No CVE-ID: None
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 [2009-03-16 01:36 UTC] mail at chernousov dot com 
Description:
------------
PHP 5.2.8 (some reason this version doesn't exists in bugreport form)
memcached 1.2.6
pecl-memcache: 3.0.4 (some reason this version doesn't exists in bugreport form)


I tried to test session redundancy with 2 servers, host1 and host2.

session.save_path="tcp://host1:11211,tcp://host2:11211"
memcache.allow_failover=1
memcache.max_failover_attempts=20
memcache.session_redundancy=2

As soon as host2 goes down, I got error: "Failed to write session data (memcache). Please verify that the current setting of session.save_path is correct..."

Next I start host2 and stop host1. Error disappears.
Changing servers order in session.save_path doesn't affect anything.

P.S. I just tried version 3.0.1, this problem doesn't appear there, all works as expected.

Reproduce code:
---------------

Patches

0001-Fix-bug-58585-Session-redundancy-doesn-t-work.patch (last revision 2013-10-22 03:03 UTC by mattc at catalyst dot net dot nz)

Pull Requests

History

AllCommentsChangesGit/SVN commitsRelated reports
 [2009-04-16 08:58 UTC] slim at inbox dot lv 
I can confirm this problem. After upgrading from 3.0.2 to 3.0.4 pecl-memcache does not write to both memcached servers
 [2009-07-10 10:57 UTC] georg dot hoellrigl at xidras dot com 
Is there someone working on that?

It also works with 3.0.3
 [2009-10-26 06:29 UTC] robyinno at tele2 dot it 
I have verified the same problem with 3.0.4 with memcached-1.2.8 and memchached-1.2.8-repchached patched.
After I have uninstalled 3.0.4 and installed 3.0.3 and everything work.
 [2009-12-15 20:57 UTC] ryan dot brothers at gmail dot com 
I just wanted to check if anyone had any workarounds for this issue besides downgrading to the older 3.0.3 release - as I am experiencing it too.
 [2010-04-09 09:41 UTC] abodera at gmail dot com 
Workaround: set session_redundancy to num_servers+1 ;)

Setting session_redundancy to 3 makes session handler write to 2 servers.
 [2011-03-11 01:45 UTC] hradtke@php.net 
This bug has been fixed in SVN.

In case this was a documentation problem, the fix will show up at the
end of next Sunday (CET) on pecl.php.net.

In case this was a pecl.php.net website problem, the change will show
up on the website in short time.
 
Thank you for the report, and for helping us make PECL better.
 [2011-04-11 00:30 UTC] hradtke@php.net 
Reopening as this caused a regression in the session handling code.
 [2011-05-09 05:48 UTC] ezequiel dot lara at mpt dot es 
(just for the record: still happening in 3.0.6)
 [2011-07-21 12:19 UTC] linusnorton at gmail dot com 
I am also experiencing this problem with 3.0.6, is there a 
3.0.7?

Also has this really been in beta for 4 years?
 [2011-07-21 14:59 UTC] hradtke@php.net 
Parts of pecl/memcache are in beta and parts are stable. The re-write stalled midway through and it has been struggling ever since.
 [2012-06-13 10:32 UTC] ea333 at freemail dot hu 
What is the regression with session handling?

I use 3.0.6 with the session_redundancy fix, and here is a little test, works 
good:

redundancy: 2 
sessionid: 4g908ob8580aj509d4vquserd7
random: 947373857
***: x.x.x.41 1
string(17) "test|i:947373857;"
***: x.x.x.35 1
bool(false)
***: x.x.x.25 1
bool(false)
***: x.x.x.57 1
string(17) "test|i:947373857;"
***: x.x.x.48 1
bool(false)


redundancy: 3 
sessionid: 4g908ob8580aj509d4vquserd7
random: 1677479115
***: x.x.x.41 1
string(18) "test|i:1677479115;"
***: x.x.x.35 1
string(18) "test|i:1677479115;"
***: x.x.x.25 1
bool(false)
***: x.x.x.57 1
string(18) "test|i:1677479115;"
***: x.x.x.48 1
bool(false)


redundancy: 4 
sessionid: 4g908ob8580aj509d4vquserd7
random: 1804507623
***: x.x.x.41 1
string(18) "test|i:1804507623;"
***: x.x.x.35 1
string(18) "test|i:1804507623;"
***: x.x.x.25 1
string(18) "test|i:1804507623;"
***: x.x.x.57 1
string(18) "test|i:1804507623;"
***: x.x.x.48 1
bool(false)


redundancy: 5 
sessionid: 4g908ob8580aj509d4vquserd7
random: 752757916
***: x.x.x.41 1
string(17) "test|i:752757916;"
***: x.x.x.35 1
string(17) "test|i:752757916;"
***: x.x.x.25 1
string(17) "test|i:752757916;"
***: x.x.x.57 1
string(17) "test|i:752757916;"
***: x.x.x.48 1
string(17) "test|i:752757916;"


redundancy: 6 
sessionid: 4g908ob8580aj509d4vquserd7
random: 12963724
***: x.x.x.41 1
string(16) "test|i:12963724;"
***: x.x.x.35 1
string(16) "test|i:12963724;"
***: x.x.x.25 1
string(16) "test|i:12963724;"
***: x.x.x.57 1
string(16) "test|i:12963724;"
***: x.x.x.48 1
string(16) "test|i:12963724;"
 [2013-08-15 03:06 UTC] mattc at catalyst dot net dot nz 
From my testing, if there are two memcached servers in the pool and session 
redundancy is set to 2 then only one copy of the session is 
stored.

It appears to be an off by one bug on line 419 of memcache_session.c:

 } while (skip_servers.len < MEMCACHE_G(session_redundancy)-1 && 
skip_servers.len < pool->num_servers);


should be:

 } while (skip_servers.len < MEMCACHE_G(session_redundancy) && skip_servers.len 
< pool->num_servers);
 [2013-09-17 20:08 UTC] tcushman at kidblog dot org 
Thanks mattc at catalyst dot net dot nz.  I was experiencing this problem with the same configuration:  two memcached hosts, session_redundancy = 2, and sessions only being written to one host.  Based on code you spotted, setting session_redundancy = 3 "fixed" the issue for the time being.
 [2021-03-25 16:44 UTC] cmb@php.net
-Status: Open +Status: Closed -Assigned To: +Assigned To: cmb
 [2021-03-25 16:44 UTC] cmb@php.net 
The official bug tracker for PECL/memcache is now at
<https://github.com/websupport-sk/pecl-memcache/issues>.

So, if this is still an issue with either of the current memcache
versions (4 or 8), please file an issue there.
 
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