stumped - data dissapearing

[Lou Kosak]

I've looked all over and can't seem to figure out why my memcache
session data is periodically disappearing.  Here's my setup:

On one server, I'm running memcached 1.2.2

memcached -d -m 1024 -u memcached -l 172.17.10.158 -p 11211

On another, I'm running a PHP 5 webapp with ADOdb session handling.
I've added functionality to session read, write, and destroy, which
looks like this:

session write modifications:

        if($memcache)
        {
            if($memcache->set(MEMCACHE_PREFIX_SESSION . "$key",
rawurlencode($value), 0, 900)) {
                Debug::notice('Wrote session data to memcache (' .
MEMCACHE_PREFIX_SESSION . $key.')');
            } else {
                Debug::notice("Failed to write session data to memcache");
            }
        }

session read modifications:

		if($memcache)
		{	
			$v = $memcache->get(MEMCACHE_PREFIX_SESSION . $key);
			
			if($v)
			{
				Debug::notice('Retrieved session data from memcache (Skipped DB)');
				
				$v = rawurldecode($v);

				return $v;
			} else {
				Debug::notice('Memcache key does not exist: ' .
MEMCACHE_PREFIX_SESSION . $key);
			}
		}

session destroy modifications:

		if($memcache)
		{
			$memcache->delete(MEMCACHE_PREFIX_SESSION . "$key");
		}


memcache stats:

    [pid] => 14287
    [uptime] => 105065
    [time] => 1183003550
    [version] => 1.2.2
    [pointer_size] => 64
    [rusage_user] => 25.541117
    [rusage_system] => 75.528517
    [curr_items] => 92466
    [total_items] => 1896346
    [bytes] => 69351332
    [curr_connections] => 4
    [total_connections] => 1875966
    [connection_structures] => 526
    [cmd_get] => 1963660
    [cmd_set] => 1896346
    [get_hits] => 1820297
    [get_misses] => 143363
    [evictions] => 0
    [bytes_read] => 1564507648
    [bytes_written] => 1644336306
    [limit_maxbytes] => 1073741824
    [threads] => 1

What I'm finding is that while browsing the site, every 5-10 page
loads I will see the error "Memcache key does not exist", but I never
see "Failed to write session data to memcache".  The site is always
able to connect to memcache (additional reporting of failed
connections is not being triggered).  According to $memcache->stats(),
I have plenty of free memory space and nothing is being evicted.  Does
anybody have an idea of what might be causing my data not to be
retrieved?

Thank you very much!

-- 
Lou Kosak
Affable Gentleman of Leisure
Seattle, WA