Hi Everyone, i have just came upon very strange corner case when doing SET
using UNIX_TIMESTAMP plus TTL in memcached running in vmware container. It
seems that on barebone servers there is no such issue.
So if the container is running for some time, eg. a week or more, then it
seems that timestamps between PHP and memcached are de-synchronizing, so
the code like this will no longer work as expected.
$mc = __getMemcache();
$mc->set("key", "value", 0, time()+10);
var_dump($mc->get("key"));
Will return false.
The workaround is to restart memcached from time to time, then it again starts
working correctly and will return "value".
Doing $mc->set("key", "value", 0, 10) will not result in same issue, so problem
might be that:1. vmware keeps timestamps counted per process and the errors are
aggregating over time
2. there's some cache for timestamp build into memcached so it's using some
internal code for getting timestamp and the errors are aggregating there
Any comments on that?
Basically it'd be good to put into docs if using TIMESTAMP+time is safe to do
on barebone servers and on VMs. Maybe some info that it shouldn't be used for
small TTLs because for higher ones 1-2 minute differences are probably
irrelevant anyway...
Thanks,
Slawomir.
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