Description:
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Hi,
when working on fixing problems with memcached after upgrading from PHP 5.3.13 to 5.3.15 recently (see bug 62801 I reported) we have discovered that we cannot use older PHP versions with the same memcached server any longer.

A simple situation:

PHP Server 1 has PHP 5.3.6 and cannot be upgraded

PHP Server 2 had PHP 5.3.13 but was upgraded to 5.3.15

Both of those servers connect to the same memcached server and use the same keys. Server 1 is a cron server so it uses CLI and server 2 is a frontend server so we connect via apache.

Before the server 2 upgrade everything was working fine - when we set some key on server 2 we were able to read it from memcached on server 1 without any problems.
After the upgrade each time we want to read on server 1 a key set by server 2 we get PAYLOAD FAILURE message from PHP memcached.

However, when we temporarily moved our cronjobs to a fresh server with 5.3.15, everything went back to normal.

My guess is that it means that some compression method was changed in PHP 5.3.14 or PHP 5.3.15 and users were not informed about it in any changelog.

Breaking backwards compatibility seems to me like a huge deal, something that you either shouldn't do or if you do you should inform about it with huge bold letters.


Additional info:

Along with PHP upgrade libmemcached was upgraded from libmemcached-1.0.2-1.el5.remi.x86_64 to libmemcached-1.0.4-1.el5.remi.x86_64

We set a following 3 options to PHP memcached (on both server 1 and server 2 of course):
$m->setOption(Memcached::OPT_SERIALIZER, Memcached::SERIALIZER_IGBINARY));
$m->setOption( Memcached::OPT_BINARY_PROTOCOL, true));
$m->setOption(Memcached::OPT_TCP_NODELAY, true));

Expected result:
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There should have been a clear information about breaking comatiblity with previous PHP / libmemcached versions. 

Actual result:
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There was no info at all.