I have installed memcached ,php-pecl-memcached and libmemcached.
1.memcached (1.4.24)
2.php5.5.30 , php-pecl-memcached (2.2.0)
3.libmemcached(1.0.18)

I try with php script test.php

addServer('127.0.0.1',11211); $stats = $mc->getAllKeys(); echo "Return code:", $mc->getResultCode()."\n"; echo "Retucn Message:", $mc->getResultMessage () ."\n"; print_r ($stats); ?>

Return code:9
Retucn Message:CLIENT ERROR

I look the log on memcached server log
<36 stats cachedump 57 0
<36 stats cachedump 58 0
<36 stats cachedump 59 0
<36 stats cachedump 60 0
<36 stats cachedump 61 0
<36 stats cachedump 62 0
<36 stats cachedump 63 0

36 CLIENT_ERROR Illegal slab id
<36 quit
<36 connection closed.

I change to memcached version 1.4.15 ,and try php script test.php

Return code:0
Retucn Message:SUCCESS
Array
(
[0] => qinyao
[1] => andy
)